Does a Rear Mount Turbo have a Lot of Lag? Remote Mount Turbo Benefits and Drawbacks Explained
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- Опубликовано: 7 май 2024
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In today’s video we will discuss rear mount / remote mount turbo setups, so engine in the front turbo in the back. We will analyze their benefits, their drawbacks, we will see if they are actually a stupid idea and along the way we will hopefully learn some important lessons and bust some turbocharging myths.
So let’s start by answering the most obvious question…why would someone want to mount a turbocharger far away from the engine? Usually the primary motivator for a remote mount turbo is space. Sometimes it is very difficult to find space for a turbocharger in the engine bay of a car that came naturally aspirated from the factory. And even when you can find the space you might require a one-off complex custom exhaust manifold if you’re working with a platform that doesn’t have sufficient aftermarket support or if you’re doing an engine swap. If you don’t have the fabrication equipment and skills such an exhaust manifold can become a very expensive item on your parts list.
And even if you find the space for the turbo the location might be less than ideal and require complex routing of the intake piping and exhaust downpiping which may negatively impact performance. On top fo this a turbocharger is a major source of heat and the space you find for it may negatively impact the components around the turbo leading to a reduced lifespan of these components.
A remote mount turbo is sort of a path of least resistance towards solving these problems. There almost always plenty of space somewhere along the underside of the car, even more so at the back so finding space for one or even two turbos here is not an issue. A remote turbo is also a one stone two birds affair because it eliminates heat problems. By locating the turbo away from the engine bay we save the engine from the added heat and we also help the turbo itself to run cooler. Companies and individuals who specialize in remote mount setups and have completed such projects usually report turbine side or hot side temperatures of the turbo to be lower by around 300 degrees celsius.
This is a pretty significant difference in temperature which helps the turbo last longer and makes cooling the turbo less important. In other words it becomes feasible to run a turbo that isn’t water cooled, instead it can be oil cooled only. This reduces cost and simplifies install. Of course, you can still definitely run a water-cooled turbo in a remote mount setup, there is no harm in even better turbo cooling.
But it gets even better. The remote location of the turbo doesn’t just save the engine bay from the added heat, it actually positively impacts performance. If a turbo runs cooler than it doesn’t heat the intake air as much. On top of this we have as much as a car’s length of intake piping that’s exposed to fresh air passing along it which means that the intake air gets cooled even more before it gets to the engine. Cooler air is denser and denser air means that we can stuff in more air mass into the same volume which means more power.
Now this cooling effect isn’t as significant as that of an intercooler so ditching the intercooler isn’t a smart idea in my opinion, instead this is added cooling simply further improves performance and helps prevent knock which means that, all else being equal, we can potentially run a higher compression ratio in the engine than with a turbo mounted near the engine.
So, it costs less because you don’t need a fancy exhaust manifold, it reduces heat and it improves performance. As you might be guessing things can’t be all good, there must be downsides.
The biggest downside of a rear mount turbo setup is that it allegedly leads to massive amounts of turbo lag. And apparently this occurs because now the turbo has to pressurize an entire car’s length of piping. This requires time and we experience this time delay as turbo lag or reduced responsiveness of the engine, in other words a car with a rear mounted turbo will feel lethargic and sluggish due to the crazy lag.
This is simply not true and I believe that this idea that a rear mounted turbo creates massive lag comes from a mis-understanding of how a turbo actually works and how it increases engine performance.
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00:00 Benefits
04:38 Turbo Lag
12:29 Boost Threshold
17:22 Oil return, noise, damage
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Note: Cylinder surface formula is not the right one for the example as it places to much importance on cylinder bases which are not important in the case of a long pipe. However, the statement is still correct and a larger diameter exponentially increases heat loss since it lowers gas velocity. More time in the pipe is more time to pass heat.
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Heat loss does not scale exponentially here. Why should it?
Also, why could have mentioned how a lower temperature makes the turbo less effective: Lower temperature = higher density = lower flow velocity. Same reason cooling the fresh air after the turbo helps, just the other way around.
This is true for the same length of tube - my question is but isn't for the same volume of hot air in the tube, the acutal length of the tube shorter? Let's say 1dm³ of hot air takes in a 2" tube (Ø5,08cm) take a total length of 49,3cm while a 3" tube (Ø7,62cm) takes a total length of 21,9cm. So the surface area of a 2" tube for 1l is 31cm² while for the 3" tube for 1l is 13,8cm²?
[EDIT] Nevermind, with the increased surface the heatloss increases, so even if in the tube there is more total heat stored, there are still 1 effect working against it: with the expansion of the volume the heat goes down (presure dropes) and even if between the turbo and exhaust valves we would maintain the same pressure the increased surface area and therefore higher cooling might(?) outweigh the total amount of heat stored between an 2" and 3" tube
@@GriderTornado It's probably possible to set up a pipe system that has higher diameter, more area in the material - and that doesn't expand or draw heat off it (type graphite, or some composite with very low heat-capacity). So it would be theoretically speaking better than a very thin steel pipe system. But you'd run into a lot of issues with it that you wouldn't have in, say.. a water-cooled PC or something like that XD Shocks, pressure peaks not being easily aligned, things like that. Or, I know parts of the physics of it makes sense, but I'd hesitate a great deal to replace steel pipes in a car.
So what the legend up there is pointing out is that if you have higher volume of a pipe, you do need to compress more air (volume, ^3) to get the pressure, and you get much higher surface area and also higher volume of piping. So there will be a lowered pressure effect as the compression builds and cools the air - long before any cooling stage happens (which is outside of the turbine step). And it will scale with larger tubing (just not exactly at that formula).
Every crazy piston head after seeing that video: "I'm gonna locate my turbo behind, insulate the exhaust line and return back the intake air through a full trunk of heat exchanger and air tank. With enought tank i can also get rid of the dump valve and benefit from the release phase to fill those tank"
Nice job
@@Sir_Cactus The loss would be linear, probably even less than that given how radiation is a mayor contributor at higher temperatures, which scales to the power of 4. So since the temperature of the larger tube is lower, the loss will be less than what the surface increase would indicate.
There are no solutions, only compromises...
Very well said! What's most impressive about your videos is I don't think you're even referencing a script for most sections. You do a brilliant job outlining the subject matter clearly and concisely but unlike so many creators, you obviously know your stuff inside and out. It's that undeniable passion that makes you such a great educator. I always learn something I didn't expect from your content. Creators like yourself are becoming more and more of a rare breed and I genuinely respect your efforts. Keep killing it man.
Thank you so much for the kind words! I did mess up the cylinder surface area thing though 😞
@@d4aYes but you admitted to that, and corrected later. You are a brilliant mind! And someone that can take constructive criticism and build on that. Very rare these days.
That's because he knows well his stuff , hence the smooth delivery of an explanation
@@d4a All good brother. You are not perfect and we dont expect it. You did pin it so ....
Well said 👍 totally agree.
Mechanical Engineer here - what he says @13mins into the video is crucial. Thermal energy is the source energy. The ''hot side'' of the turbo is just a gas turbine and the simplest form in thermodynamics to relate the work done (Wout) by a gas turbine is Qin = Qout + Wout.... Qin - thermal energy IN, Qout - thermal energy OUT, Wout - Work produced. This is the basic thermodynamic law of any heat engine and this will make it easier to understand the basics on how a gas turbine or engine work from a scientific perspective.
So when you relocate a turbo to the rear, there is heat loss in the exhuast gas, therefore your Qin becomes less, resulting in your work produced by the turbine being less which is not good. The turbine side of a turbo is designed as a adiabatic system meaning they try to make it as insulated as possible because any heat loss is just a loss in potential energy - therefore turbos are manufactured very robust. Obviosuly there are China turbos too which dont comply to this but every big turbo manufacturer designs there turbos to run at very high temps so a drop in turbine temp is again not really a win w.r.t turbo life span. (This is why modern car engine designers put the turbo as close as possible to the exhuast manifold).
Now this issue of charge air being too hot can very easily be solved by selecting the correct intercooler, but I also know space is usually a problem - a short fat intercooler is not as effecienct as a large thin one. If you want to learn the in depth science of intercoolers, go look at Gale Bank's videos on intercooling, he explains it very simple and easy.
Remember folks, chase efficiency, not power. Power is a by-product of eficiency. If you build an efficient, well designed engine, it will produce more power at less stress levels.
My initial thoughts where more along the lines of conservation of mass (flow).
As the air cools, it gets denser, which means it will travel slower to keep the same flow of air in weights per time unit.
Basically bernoulis principle, except with gas density instead of flow diameter.
That's why you wrap the exhaust system.
Too high of temperatures is the Achilles heel of internal combustion engines. The materials we use have a much lower heat durability limit to fully use the potential heat energy in the fuels.
I'm with that notion and believe if I'm wrong but could reduce nox right? It came to me but my brain just turned on so forgive me
So glad to see the steady growth in viewership of this channel over the last year or so. This video is pretty damn niche, even among auto engineering videos, and yet it has almost 200k views in just two days. Love to see that because it's very well deserved. It also shows me that there's still a few knowledge-seekers left in our increasingly vain, self-obsessed world
I feel like the vain are just louder and more prominent, not necessarily more numerous. At least I hope...
@@d4a I feel like ego(narcissus styled ego specifically) is almost a form of infectious social disease. The more its allowed to be exposed to the social order, the faster it spreads. Combine that with the increasing pressures of economic stresses pushing people into more competitive behaviors double stacking on the ego.
Then a third and fourth stacks of echo chambers and self-serving disinformation, confirmation bias inputs basically, which humans have never had this level of access to.
@@d4aone thing id like to know is- looking at the differences in the dyno graph.... just how much improvement in building boost would you see by wrapping the exhaust and headers to the turbo??
669k after 2 months. Crazy good numbers for the topic.
Decades ago I had a C4 Corvette ZR1 that was modified with a remote mount turbo. Yes it had noticeable boost lag, as you will undoubtedly have with an 83mm turbo, but the remote mount I think contributed to a more subtitle boost ramp. Also, the added air volume meant that the turbo was far less interrupted by momentary throttle cuts as the transmission shifted. All in all, it was a 9 second car every day of the week, and breaking 200 on a one mile was easy.
Beautiful
would you recommend the c4 as a first car or are they hard to work on?
@@yeetmeme6027 No not particularly difficult, they’re a Chevy. They’re a parts bin special. The ZR1 is the only one to avoid, unless you have deep pockets, as the engine is a special, 1 vehicle only engine. But all the others had a tuned up truck motor.
The manual transmission in early C4’s is a bit funky. GM was trying to do a thing, and that thing didn’t really make much sense. But later models had a BorgWarner T5, which was plenty stout enough for the power it produced. If you’re planning to swap to a modern engine, like a 5.3, then you’ll definitely need to upgrade to a TKO or T56 transmission because a bone stock 5.3 straight out of the wrecking yard will break T5 on the first rip.
@@yeetmeme6027 I second @davidblalock9945 on this bit. Not difficult, just quirky and some quirks can be expensive. My first car I still have to this day is my 1996 Chevy Impala SS. Pain in the ass to find suspension parts for, but easy enough to work on.
@@davidblalock9945 isn't an 83MM a pretty huge turbo for that engine size? I would be more inclined to blame turbo lag on the fact that you say this was decades ago before the incredible boost management we have now paired with a fairly large turbo for the motor it's feeding.
Fun fact. The WW2 era P47 Thunderbolt had a turbocharger located in the rear of the fuselage, well back from the 2,800 ci. (45 litre!!!) twin row 18 cylinder radial.
Don't forget that aeroplane engines run pretty much at a constant speed - they don't have to worry about spool up speed.
Also don't forget that the turbos in plane engines are always by themselves in separated chambers so the heat doesn't fuck anything...
@@mrb.5610 Dude....this is a WW2 warbird! Ofc it was designed to handle extreme use of the engine ...
True and the same goes for most ww2 turbocharged planes
@@ronnysundt3249The turbos for the b25j20 engines were located at the back of the engine nacelles for the same reasons, but also for the fact that if shot at from the rear, the turbo would be the first thing hit. Yes, the engine would lose a fair bit of power, but at least it would still run until the oil leaked out, long enough at least to get to a FOB for repairs if the bomber survived the encounter. The B25 was a frontline bomber, so it was designed for increased survival rates against flak and small arms fire. It was kinda between an attacker and a bomber. It had 6 .50cal Browning M2s on the nose, 2 gunner turrets with 2 M2s each, and two side gunner positions with 1 m2 each. It had a payload capacity of 12 250lb bombs, 8 500lb bombs, or 3 1000lb bombs. Dammit, now you got me wanting to play war thunder again. Bastard.
Great explanation. I worked at STS back in the day and i dont know how many times ive explained the remote turbo lag myth to people. The best argument was just giving them a ride - the average car guy could not tell the difference from a remote mount vs under hood mount system (other than the exhaust note of course).
Guess I don’t have to share this link with you….
its fun hearing dodo heads say the sts turbo kit was stupid because " it only made 7 psi" *eyeroll*
I had a STS kit on my silverado back in 2003 or 2004. Fun times!
Confused everyone cause nothing noticeable was under the hood and stock exhaust manifolds...
Did you live in Utah?
@@nickdeluca7742 I used to, went to college in Provo
16:40 Small correction: the 2pi*r^2 term of the surface area formula represents the two circles at the ends of a cylinder. In the case of an tube like an exhaust pipe these are absent, therefore A=2pi*rh (hence a 10% increase in r will increase surface area by 10%, etc)
Shouldn't the correction be that it is the volume of the cylinder that is important.
Where we again find an r^2 term.
Since the area ahead of the turbo spool needs to be pressurized (filled with exhaust gas from the engine) before the spool starts to spin up.
@@noer0205 Not in this case, he's talking about heat loss- which is related to surface area.
The increased area (The R^2 term) would be a factor in the lag/delay that is attributable to the time time it takes to flow the amass of air in the pipe as you said. This seemed to be pretty negligible relative to the rate of flow of a turbo even if it increases by area instead of radius- at least according to his calculations.
Came here to say the same thing
The dyno graph label is also wrong. He labeled "front/rear mount torque" on the power curve, not the torque curve. Torque tends to fall off, but power will still increase due to RPM. 12:49
Indeed
one extra thing to consider:
all the infrastructure (piping for oil, air and exhaust gas) is going to add more weight to the vehicle, which does effect performance, but you are also lowering the cars centre of mass since you're installing it all way down low so it might also have benefits.
If it's hanging off behind the rear axle, I'd say definitelynot good for handling but probably good for straight line traction.
If you have a front heavy car it could also improve weight distribution as well, very slightly but every little bit counts.
And you are moving the mass to the rear, which is nearly always good
@@piccalillipit9211 'Simplify then add lightness'.
Colin Chapman.
Not that much weight, the turbo is going to be the heaviest part that you are adding. You will have to run a scavenge pump for the oil drain to get the oil back to the engine. Still not very much weight
Nicely explained! I appreciate the distinction between Turbo Lag and Boost Threshold. So many car enthusiasts equate the two terms, but as you said, they are not the same!
I agree with you, especially when the enthusiasts are journalists and should distinguish the two, but I wish he didn't explain the implications here incorrectly. Boost threshold is concerned with steady state operation, in which the volume of the tubing makes little difference other than thermal losses. Lag is concerned with the total energy in the system at a given time, so if you have a large pipe that needs to change in pressure by one atmosphere or more, that's going to take a noticeable amount of time.
I've played with remote mount turbos through the years. They are surprisingly effective, the thing I found mostly different was that it has similar gains to a log manifold even with tuned header(s). This makes sense because you are using a much higher amount of built up static pressure for the turbine as opposed to the individual exhaust pulses of pressure - so even tuned headers are working against a much higher base pressure. It is sort of the extreme opposite of cleanly delivering the pulses and eliminating the base pressure buildup like you get when dividing an exhaust between multiple turbo scrolls.
Your videos are always so informative. I learned a lot with this one. While I've never really thought about this kind of setup, I definitely went straight to "oh man that's gotta increase the lag" and now I know how that is wrong frameset, and the "heat energy" vs. kinetic explanation was great. Thank you again all around. Great work!
Perfect video. It is frustrating how many people look individually at pressure and flow but it is prevalent throughout the engineering world! A pressure washer with 2,000 psi is not more powerful than a get engine with 700psi discharge pressure (50:1 EPR) You describe things so clearly, please keep it up. Another fantastic video. Clear and concise with common sense easily relatable concepts. 👌
CORRECT - I have had so many arguments with people, in an ironic way high PSI is BAD. High PSI is a result of NOT being able to get the air into the cylinders. What you would REALLY like is STP [edit: standard temperature and pressure] and huge air VELOCITY
EDIT: his is why a jet engine is so powerful - you can have the massive air velocities cos its not a fixed volume of combustion. You have to have high PSI cos you cant get the air VOLUME into the cylinder without compressing it.
@@piccalillipit9211what is stp and where can I go to become smart like you
@@asianboyyy117 - OH sorry - STP is standard temperature and pressure and the answer to your second question is a book called " Turbocharging and Supercharging" by Alan Allard
Yes i can recommend this book. @piccalillipit9211
Ok, I understand that high flow restrictions or any restrictions can reduce effective boost. But can you explain how a big turbo with 14 psi and a small turbo with 14psi make different power. Only thing I can assume is that he's measuring boost at the turbo outlet. But if you measure at the intake valve or intake manifold, and two different turbos produce the same boost what's the difference? Assuming you have a good intercooler and the temps fall to more or less the same temp what's the difference. It's my understanding that boost is usually measured after the intake valve, after the turbo, and therefore any flow restrictions in the turbo are irrelevant.
To calculate the spooling up time you should use the cfm of the engine not the turbo. It will be depend on the volume of displacement, the RPM, the volumetric efficiency of the engine (and exhaust flow, which reduces when lengthening the exhaust) and the inertia of the turbo compressor itself. The last thing is to regard the back pressure on the Turbo. If in any case all the inlet valves are closed, the turbo pressure will increase rapidly but the volume displaced will be 0.
Yeah, he was acting as if the cold side of the turbo is routed back into the exhaust or something. Leaving out that variable makes the whole message of the video relatively incorrect. It is like a game of Telephone because this guy seems to have to heard most of this stuff on youtube and is just relaying it back in the video.
I've been subscribed to your channel for about 6 months. I enjoy how informative and in-depth your content is. Thank you.
A video on the pros and cons of a hot-v configuration would be a nice counterpoint to this.
This video, and the series on turbos, is *almost* perfect.
The only disappointing thing in this entire series on turbos is the you haven't once used the iconic bass riff from Queen and David Bowie's "Under Pressure."
😏
That’s how you get content id’d and demonetized instantly.
Very well done mate. What a fantastic video. So much information crammed into it (which was all relevent to the subject) but more to the point, this was for the first time in a long time where i havent found myself getting easily distracted or catching myself bailing out after 10-15 minutes because of the lack of interesting content or poor delivery of it. In fact I think this is the first time ive bothered to comment on any video in all the years of watching youtube, so thats speaking volumes right there. This is how you're meant to get people to like and subscribe, not by begging them to. I've not seen any of your other videos but you've already got my sub mate.
Plus on top of all that, Im gonna bet that English most likely isnt your native language, and you still delivered it clearly and I never missed a trick. Honestly you killed it guys. Bloody good on ya. Very good form.
Thank you so much for the kind words of support! But it's not guys, all of it is just 1 guy 😁
I love how easy to understand you managed to explain the entire topic and the reasonings behind it. Amazing stuff !
I've had experience with two vehicles with rear mounted turbos. One was an early 2000 model Z28 and the other was a Nissan Hardbody pickup truck. Both vehicles ran extremely well and were daily drivers.
That hardbody sounds glorious
Thinking about this setup on my 80 datsun 720 with a l20b, would be pretty crazy with side draft carbs too
@@ddzn80My dad was the original owner of a 1980 Datsun 4X4 king cab truck.His truck was modified, Custom red&gold metallic boat flake paint, 33” Michelin, off-road tires,custom rims,Rancho suspension,5” body lift, aftermarket stereo system,
Weber carburetor, aluminum, aftermarket intake & filter,hand crafted fiberglass camper,Aftermarket glass quad headlamps, PIAA Jap made bulbs,Aftermarket taillights…RIP Dad
I ran a rear mount turbo well midmount, on a 2000 camaro ss. I miss that car she was amazing.
Woah that's awesome. I'm looking into a rear mounted setup for my 95 z28. There is so much room back there, with zero room in the engine bay.
The remote mounting of turbos was the norm in aviation such as P-38, B17, P-47 etc. the long exhaust duct actually cooled the exhaust enough to avoid damaging the turbine.
Only because the first generation of heat resistant steels weren't that good ...
@@mrb.5610 It was all size and packaging; no one cared about "longevity" of replaceable parts.
Remember that in wartime the average life of the aircraft itself was maybe just a few missions.
@@arthurfoyt6727 Not sure 'longevity' comes into it - the turbine blades either melt or they don't - they don't exactly wear out !
Perhaps bearings could be affected by temperature? @@mrb.5610
@@mrb.5610 The Germans were happy with 10 hours service life on their jet engines. Replacing just a turbo in 10 ours is child's play. In wartime you only cared about winning.
Absolutely brilliant explanation, I’ve been super curious on these rear mount set-ups for a long long time. Thank you.
I had dreamed of a remote turbo s197 v6 (the crappy 4.0 v6) mustang build. A lot of people online said all the things you pointed out in the beginning about excessive lag and such. And as always, you clearly and concisely explained everything. Then as a bonus, I also learned how variable geometry turbos worked from the included clip.
Another great video, thank you. I’ve always been curious about this and had assumed lag would be bad due to the distance from the engine. I was wrong! Great explanation and presentation. You make complex topics so easy to understand.
I mounted my Turbo Charger hanging out my passenger window.
My God you've done it.
An excellent presentation - thanks! I can almost hear Gail Banks applauding, somewhere in the distance... 😎 Keep up the great work!
you're an excellent communicator and this video is so well presented, information dense but explained very clearly. will be sending this to everyone that comes at me with a whack understanding of how turbos work!
Great video. I was directly involved in the STS turbo thing. I got tired of trying to explain just what you discussed in the video. Especially the lag.
My biggest problem was the position of my exhaust manifold, now that turbo lag is not a big problem in my case, I will be using the rear mounted setup
I am so gratefull
Congratulations on 1M subscribers man. Absolutely colossal achievement. I've always believed you would be huge, but this is wild! So well deserved.
Started watching you recently, with your video about the differentials, and honestly I enjoy watching your informative videos now. Great Stuff!!
I've been considering a rear-mount turbo in my project car, for two main reasons:
1) Weight distribution -- My car is already front heavy. A traditional turbo setup would exacerbate that.
2) Exhaust sound -- I have long tube headers, and love the sound. A turbo manifold will make my BMW sound like a pickup truck.
Weight distribution is something not discussed, and it can really help balance things out, particularly on a mid-engine car with a front mount (remote!) intercooler. The other unmentioned benefit is cops will rarely find a remote turbo, because, well obviously, when they make you pop the hood it isn't there :P There can also be a reduction in drag (passive up-pipe cooling vs FMIC) which can be non-insignificant.
I would like to hear more about the heat energy recovery in the turbine… from my Navy days it was my understanding that the majority of the energy exchange was from expansion through the turbine, less about our typical view of kinetic energy from impingement and more about expansion from hot high pressure to cooler low pressure. Maybe too fine a point, but I can see why close coupled turbines would harvest much more power during the blowdown phase particularly when paired with an early exhaust valve opening event… I’m also wondering if a remote setup would benefit from cam timing changes that would increase exhaust gas temperatures down the length of the pipe. Also seems that you could better manage front to rear weight ratios with remote installations.
Flow is always from higher pressure zone to lower pressure zone so you're definitely right.
Hence pressure differential
Richard Holdener did front vs rear mount turbo tests adding like 10ft of piping in between the exhaust and turbo. The max power level was exactly the same. What the increase in piping did was delay when the turbo would spooling. The difference in spool was not very large perhaps 500 rpm. If the spool was important you could change the AR of the housing or use a smaller turbo that spools earlier. Also he did not use heat wrapping on the turbine side piping.
You've nailed it again my friend. Brilliant presentation, well researched !!
Great explanations bro, am very impressed with your ability to explain complicated engineering in a way that a layman like myself can easily understand.
Cheers from Australia
I love your explanations!
Holy cow... I had no idea this was a thing. My first thought was when Subaru said they couldn't stuff a turbo into the BRZ because there was no room, and some crazy people were shoehorning turbos into the bay by chopping holes everywhere. Now I'm fascinated with the idea of a rear-turbo BRZ.
Not like I'd be ditching my WRX, of course.
I akso just thought about so many cars I owned or want to now to run this lol. Like how the fuck I never heard or think of this since I bought my first Turbo car 20 years ago and fell in love but always wished I could move it away from the engine and get the heat down, 2 decades and now it seems so simple 😆 😆
- and many dragracers - merely mount the turbo outside the hood... Everyone loves a set of horns on their V8. :) )
My son has front mount turbo in his Toyota 86, which is the BRZ rebadged. No fancy hole boring, it can fit when it's done well.
If you believed every RUclips mechanic, there'd be no Subarus except for salvage yard enthusiasts who enjoy destroying engines on purpose
One of the best explanations I've ever heard. Bravo my good man.
I am very new to auto mechanics and you explained everything so well, I had a really easy time understanding. Amazing content!
One major problem of the remote rear-mounted turbo is the absorption of dust and debris from the ground into the turbo and damaging them
Very good! The overall effect is a "lag" but we can slice that up with your definitions. I think this is a very good method for cars that were never envisioned as turbo. There should be some weight loss benefit. As exhaust are very heavy usually.
Thank you for your exceptionally clear explanation of turbo addon to engines. This is very rare so keep up the good work!
Your vids are quite honestly, Spectacularly good and clear and well reasoned, love your work, thanks
It is absolutly true that it is important to reduce the cooling of the exhaust infront of the turbo, yes, and that can be achieved by a smaller diametre exhaust, as in increase exhaust gas velocity and has a smaller surface area. However, the formula required to calculate this surface area does NOT include the radius squared. The 2×Pi×r^2 are just the two circles on either end a cylinder, which we do not have, as the exhaust pipe is a pipe and not a cylinder.
If you're measuring 1 bar at the intake manifold that's all that matters. Doesn't really matter if it's from a 30mm turbo or an 80mm turbo. The airflow is the same. (unless the temperature is significantly different as you mentioned)
It's basic fan laws and fluid dynamics. If you change something downstream of the pressure sensor however, then that 1 bar could mean something totally different.
Also, flow and pressure are related by a function of square. So yes, doubling the pressure doesn't double the flow rate. The calc for determining new flow rate based on static pressure change is CFM2 = CFM1 x Sq.Rt(SP2/SP1).
So for example: 7 psi making 1000 CFM would mean 14 psi is only making 1414 CFM.
finally someone that called this out also eqn mdot=(P/RT)*(pi*r^2)*V. unless the velocity (V) or temperature (T) is different then mass flow rate would be the same but i wouldnt expect it to change significantly
I e-mailed the video creator about this. The thing is, he's not wrong. Nothing he says is wrong. I would call this the "you're not wrong, you're misleading" category. Here's my comment (that got buried in the comments)
Regarding the turbo size - I just want to warn people to carefully listen to the video to not come to the wrong conclusion (like I did initially and embarrassingly e-mailed the author about it).
You can't just put a bigger turbo on the same engine and magically make more power at lower intake pressures.
The video states "which one makes more power?" And the conclusion is the bigger one can make the same power at lower pressures. The question asks nothing and also assumes nothing about the engine being matched to the turbo. Later, the video also states "match your turbo to the engine".
So, if anyone is still confused about this:
In a car engine, turbos are regulated - through intake pressures. Turbos don't just simply work at 100% of their air flow capacity during the engine operation, in fact, that is rarely even a thing, except maybe in some diesel engines with small turbos. Air flow doesn't magically stay the same at the same engine RPM and the same engine capacity but lower intake pressure. In his example, we are flowing the same amount of air into the engine with a bigger turbo (and lower intake pressure). But how? More engine RPM? More engine capacity? The question doesn't bother itself with that and doesn't assume anything. So the answer is right. Same airflow, same power. It doesn't care about the package. Just the turbo. But if we are talking about the real world, where you usually modify the same engine, the intake pressure IS ACTUALLY an indicator of airflow at certain engine RPM. There is no way around that.
Bigger turbos DO make more power, but only if the engine parameters change. That's the only way you get more air into the engine at lower intake pressures (more RPM or more capacity). Boost controllers work by regulating the intake pressure. And if BOTH the turbos can maintain the same air pressure, what actually happens is we have the same air flow. The boost controller is simply regulating the bigger turbo to run at a lower speed, providing the same air flow as the smaller turbo and maintaining the same air pressure.
Example: You set your boost controller at 14.5PSI. Your smaller turbo worked at 80% capacity at 4600RPM (for example). Keeping the same boost controller setting at 14.5PSI, this means your bigger turbo is now working at 20% capacity, keeping the same air flow (again, just an example).
Engines are not magic. They can't magically take more air flow at lower intake pressures. This is why a bigger turbo might not make more power. It can only do that if you go into higher RPM, make the engine bigger or make more boost - all parameters where the smaller turbo can't keep up the air flow and ergo... The intake air pressure.
If both the turbos can keep a certain intake pressure throughout the whole RPM range, this means they can both provide all the required air flow for its operation. It'll be more or less the same amount of air flow. Again, turbos don't always (in fact, almost never) work at 100% air flow capacity. Their air flow is actually regulated through engine intake air pressure.
The questions and statements themselves don't assume keeping the same engine parameters. They only ask how much power the turbos themselves can make. The author later even says you also need to match your turbo to your engine.
This is a warning to anyone watching this, - be careful not to misunderstand this. Your 1.6 turbo gasoline engine will not make more power if you give it a bigger turbo with a lower pressure on the boost controller setting (unless you're going significantly into higher RPM). The question doesn't assume you're keeping the engine parameters the same.
Big turbo makes more Power with same intake pressure because have less backpressure in exhaust.
Finally found this comment, higher flow rate means nothing, the only meaningful thing is pressure at the intake, very misleading video in this part.
Very, very informative and well put together video. It held my attention the entire length. Very good job, you have a new subscriber here.
your videos makes understanding about ice a lot easier keep the work man you r helping automobile students like me in a lot of ways keep up the good work
Excellent video, as always. Just a comment about the small vs large turbo both giving 1 bar of boost (timestamp 5:50): from the engine head perspective if 1 bar of pressure gets there it does not matter if the turbo that generated the boost was big or small. For a given engine, if the turbo can provide 1 bar of boost then that determines the amount of extra fuel that can be burnt in the cylinders.
True. If the same turbo flow was applied to two different cylinder heads, one high flow and one low flow, the boost would be higher on the low flow head. With more turbo flow, the higher flow head could read the same boost as the lower, as the whole system flows more air.
I was wondering if I was missing something, but I tend to agree with you. 1psi for a given intake volume (engine volume, efficiency) will make the same power no matter the turbo size. The blowoff valve might be working harder with the larger turbo, but still... And you could have a turbo small enough that it couldn't produce 1psi for a given setup , or a turbo too large for that setup. Otherwise I generally agree with the video.
@shadwills8594 No. The restriction in the small exhaust turbine side restricts airflow. Airflow makes power by having more air available to burn fuel. Put a less restricted hot side on the turbo and the compressor side of the turbo won't move enough air to make boost. It's a balance.
Well this is timely. I have a "Stealth" remote mount turbo kit on order for my 2006 Miata. The lag and boost threshold have been debated to death on the forums, so I'm going to see what it's all about. Great video as always man! 👍
It would be really cool if you could record a video about it and put it on your channel! There are basically no videos online discussing installs for smaller displacement engines and I'm sure lots of people would be curious about it.
@@jiijijjijiijiij Sure. I'll definitely do some videos about the boost response and work it into my track videos. TBD if we do installation videos. It's a pain to do work and film at the same time in a driveway with cars driving by.
@@TurboHappyCarRemote-mount your house.
Fantastic! I was only looking at Daigo Saito's MX-5 with spare tires on the rears drifting in 1st gear from an exterior perspective without mentioning the build
If ever went rear mounted I would definitely go anti lag just for the critics lbs
Thank you for this. You are one of the few sources I trust to provide accurate information on this topic.
Thank you for killing the myth with straight forward facts. This opens up location and design placement of a new system. Wonderful!!!!
Thank you for taking this topic up. I have been thinking about rear mounted turbo setups for years now.
This video feels like a more fun university lecture
this channel is a gem! Thank you for sharing all this stuff!!! ❤
Damn dude you really blew up and I’m happy for you!! I remember back 2 ish years ago you just explaining engine stuff and your mr2 project and now you almsot have 1million subs
Bro really said "jokes on you heat energy and kinetic energy are the same thing" and I had a revelation and went holy shit hes so right lmao
Right when I thought I knew how turbos worked and that “duh obviously having the turbos farther from the engine causes lag” you make a new video and I realize just how much I don’t understand! Awesome video!
Like always great informative video brother! So much misconceptions surrounding turbo lag some common sense goes a long way.
Thank you for teaching me something that I didn't even know I didn't know! Your videos are always worthwhile.
You explained the boost threshold well, i see it like by having the exhaust longer and losing heat, that'd make the gasses more dense and less volume which means less flow. not what you want to feed your turbo.
the volume stays the same, the thing that drops is the pressure, remember the ideal gas formula, pV=nRT, the pressure is directly related to the temperature in that formula, the gas will occupy all the volume it is allowed to, and the piping has a fixed volume it can take, so at the end of the day, less temperature is less pressure, and the turbo needs that pressure as well
you can also add bernoulli's principle into the mix to add in the flow of air in the pipe related to the pressure
it's an interesting topic
Boost pressure is actually quite important. Mass air flow is indeed the important metric, but you have to put all the air into the cylinders. The volume of the cylinders is limited, meaning the only way to put in more air is to increase the air density. As you can not cool down the intake air infinitly, you need to increase it's pressure, meaning you want high boost pressure. That being said, mass air flow is still important, as building boost pressure requires lots of air and the larger and higher revving the engine is, the more air leaves the system through the exhaust.
Exactly. The CFM (airflow) going into the engine is directly linked to the boost pressure.
You can not simply say a turbo "has" 15 psi.
He also didnt take into account that the exhaust pipe can be relatively cold wich initially draws extra heat from the exhaust gas.
I doubt if the exhaust gas speed is correct, did he take into account that it is also pressurized until it has been trough the turbine?
@@willemstark4733 The exhaust gas cools down in the long exhaust. This means it reduces in volume and slowing down. Same pricipal a jet engine uses, but in reverse.
I did not deny that.
The only thing what makes this effect worse was not mentioned.
Excellent video and explanation! I really enjoyed seeing the bottom of some of those modified Nissans. Your content is of extreme high quality! 😃
I still can't believe how good you are at explaining. You're amazing!
Holy smokes dude! As a child growing up in the 80s turbo era, I initially assumed turbos were rear mounted and I felt like a moron when I discovered they were “hiding” deep in the engine bay! Thanks so much for this video! ❤
Some were rear-mounted, I think the 6R4 had rear mounted turbo's
Oil to turbo shouldnt be big problem use a Oil cooler and a tank with eletrick pump and you can have a closed setup.
Complicated. You'll need a high pressure pump for the turbo AND a scavange pump for the drain. More things yo go wrong !
Plus something not mentioned is the extra weight of the installation - especially hanging behind the rear axle.
It won't improve acceleration times or handling !
Hahahahh, what?
lots of guys run water tanks in the back for heat exchangers so why not? you'd have to monitor that oil pressure in addition.
@@mrb.5610I ran a bed mounted turbo on a 5.7 LS for a few years, single 6-8psi oil pump was all that was required, no scavenging or high pressure pump required. As he said in the video, remote mount turbos run much cooler, so the oil isn't required to do as much cooling, just lubricating.
Oil drain ran down into to a 3 quart tank, directly below the turbo, pump mounted below that, discharged through a power steering cooler, then through the turbo. A pressure switch would activate a warning light on the dash, if pressure dropped below 4psi, only a couple seconds on cold start. Ran some super duper expensive oil, specced by the turbo supplier, didn't change it the entire time I had the truck.
I carried a blanking plate, so I could remove the turbo core and block off the turbine housing, if something went wrong with the oil system and never needed it.
After this video, I think I need to build another one.
@@aaronnoyb As someone who likes the idea of a closed loop as a solution and was wondering what would be required for it, this is really useful info. Thank you.
You're a smart guy thank you again for teaching me about the technical side of cars and their modifications 😊
As always, so well explained, thank you for sharing!
Bro always speaks like he's recordings at 1am and doesn't want to wake up his roommates.
Just shut up and enjoy go make a meme account if u wanna be so funny
It’s peaceful
@arthur_za, I've just watched this at 1am and I didn't wake up my wife or my 5-y.o. son 😂
lol lol lol bro I thought the same thing and then saw this comment lol lol fffffuck lol
It will still mess with your throttle response though. Many F1 teams have transitioned to a water-air intercooler setup to reduce overall induction system length. Some of the recently demo'd engines seemingly didn't even care about having equal length exhaust manifolds if it meant a shorter overall exhaust valve to turbine distance which arguably is more due to packaging reasons but does also help throttle response. But most importantly, a shorter (and straighter) intake system will incur less pressure loss. The only important "quality" of air for a combustion engine is the oxygen content; since the engine can only consume x volume of air at y pressure, the increase in air volume won't do much or anything at all to increase air density (thus oxygen content) in the combustion chamber and pressure becomes the deciding factor. If you have more pressure loss in your induction system, you will have more turbo lag by default to make the same power as the pressure at the turbo has to be higher to compensate for the losses.
This doesn't mean rear mount systems are stupid or make your car undrivable, it's just that they will incur a noticable dip over an equal power setup in terms of responsiveness. The one other benefit for rear mount systems I can think of is that the turbo inlet air temperature is going to be lower than typical engine bay setups. Yes, this can be avoided if you duct your intake correctly, but often people just run a filter directly on the turbo inlet to reduce cost and complexity. Otherwise, great vid.
What pressure losses? If your pipe is sealed, it can be as long as a gas pipeline of million meters, as long as it's filled with "technical gas" for pressure, you get an immediate outcome on the other end when you put some in on this side. Technical gas kind a stays always in the sealed pipe.
The only quality of air that is important is oxygen content?
Ok.. So when the intake charge is hotter than expect from, say a heat-soaked intercooler, and you start running into detonation; would you argue that the temperature of the intake charge is not relevant? Oxygen content is not the only relevant thing.
Don't spread ignorance.
There is NO WAY
Intake temps under the car are less than in front of the car
@@SupraSav Hotter intake charge means less oxygen content because hot air is much less dense than cold air. Detonation and pre-ignition from hot intake air temps is due to said temps dramatically affecting final combustion chamber temperatures. It's also one of the main ways HCCI engines control ignition timing, hotter IAT for more advanced timing and colder IAT for retarded timing, with a fairly narrow operating window for usable performance.
@@phillgizmo8934 It's technically not a sealed system and even if it was the fact that you're actively forcing a fluid (air) through it changes the dynamics completely. Any extra length, bends, restrictions (intercooler core, throttle etc) will alter the flow of the air through the system and potentially reduce final air pressure depending on what that piece is or is designed to do.
the explanation I didnt know I needed on a topic I didnt know existed. you just changed my entire paradigm on modifying my cars
Thanks for making me smarter. I really enjoy and appreciate your videos. They are packed full of knowledge and make learning fun.
Another benefit of rear mounted turbos: you can make your engine bay look like normal so people think your car is not fast without knowing you have a sneaky turbo 😂. Great for trolling
Also turns out that I have been mixing up turbo lag and boost threshold. Thanks for clearing it up
Definitely! You can be very stealthy with it
Join the club. I mixed those up too.
Great video although i do disagree that a bigger turbo makes more power per default! It will however have a greater potential for higher airflow and thereby power IF the engine can handle and sustain that additional flow.
There was a time (in Sweden) when turboing with old semi-truck turbos was popular and cheap, although the engines would not be able to produce enough exhaust to spool the turbine. So adding a smaller turbo would, at that point, outpower the bigger turbo.
Although thanks, really like your contents!
Turbos are technically engines (heat pumps) in their own right, and can be defined in horsepower like an engine (compressor maps are basically dynographs for turbos). If you have a smaller turbo that makes more power on a trickle of fuel (exhaust) than a big turbo that doesn't spin up with that amount of fuel, well it's probably true the car doesn't move as much, but the bigger turbo should always makes more power for the same RPM at peak efficiency. The AR ratio (one axis on compressor map, equivalent to torque) is defined by the intake/volute circumference difference. You'd never say a 6.6L Duramax makes less power than a 1L Miata, so long as you're stuck with miata injectors. It's like, yah, of course.
Great video, you have great knowledge & are passionate about teaching & explaining. Thank you! I'm going to watch this again, to learn more! Paul
I always learn something new watching your videos. Keep it up!
Very interesting info. The first thing I thought was that the turbos and intakes will be prone to damage and water ingress.....I'd driven through 30cm of floodwater this morning, it looks like I would've been stranded if I had a turbo like the ones shown !
But if you had to turbos you could go fast enough to skim over the surface of the water.
Never drive through flood water.
@@kermitthehermit9588never say never. Generalizations like that are not helpful. Definitely take extreme care driving through flood water.
@@jaredlancaster4137 There is very little difference between 'extreme care' and 'reckless abandon', in any practical sense. Nobody drives into a flooded road with the intention if being up to their neck in water.
@@frankcooke1692 the difference is checking the depth before you drive into it. I'd say thats a very practical difference.
16:10 the relation between heat loss and diameter is linear. At 16:20 . the 2*pi*r^2 is to calculate the area of the the two caps of a cylinder. in a tube without caps such as an exhaust pipe, you are only interested in the surface area of the "wrap" or the tube section. which is calculated by pi*base diameter*length of the cylinder. so the relationship between the diameter and surface area, and thus heat transfer is linear
yeah, pretty rough mistake considering the end-caps!
Consider that when you double the area, exhaust gas will have 4 times more volume to expand and therefore highly decreasing its temperature.
Excellent work! The thing I like most on your educational videos is that you always try to deconfuse terms that are considered the same but certainly aren't like ( Turbo Lag vs Boost Threshold ) which I understood which thing is which after Iwatched your video so thank you very much for that!
Cheers from Greece, Keep Up and let's have a better year than those previous 4 that were certainly nightmares... Jim
Thanks, love your vids.
Always well researched and explained in an easy to undersand way.
I'm thinking that it might be beneficial in a rear-mounted turbo to implement an entirely separate dedicated dry sump and electrically driven pump to drive the oil to feed the turbo.
absolutely, great idea
Nice one!
Another benefit is that you could actually run a VGT (variable geometry turbocharger) on a petrol setup. You mentioned the VGT but did'nt elaborate on the fact that you only find them on diesel engines because the exhaust temperature is lower than on a petrol engine. Since they wont survive petrol exhaust gas temps.
Would make a lot of sense to remote mount a VGT if the exhaust temperature is about 200-300 Celcius lower, and fix the downside of the raised boost threshold. might even improve it.
Porsche utilizes VGT and have for some time now..
Nice I was actually debating between turbo and supercharger, this makes my life so much easier. Thank you
Thanks, great informative video. You used great analogies good fluid mechanic examples. Easy to understand. Brilliant.
I think they should put a metal mesh screen over the air filter for better protection for the air filter so dirty air doesn't blow in easily
The surface area of the exhaust pipe will be dominated by the walls, not the ends, thus a 10% increase in the radius will lead to ≈10% increase in the surface area.
The ends do not even exist! The exhaust pipe is a pipe, not a cylinder.
Aren't you guys just trying to speak about the containment volume of a cylinder? Which is nothing but the area of a circle, times length? Gas flow is a lot like water flow, just much less dense. You have both a volume of water and a velocity. You have both a volume of gasses and a velocity. Diameter of the plumbing affects volume and velocity, one way or another.
Volume of the pipe is dominated by the radius. So actually go with the largest pipe possible to avoid heat loss. But with a small pipe you get higher velocity. It’s a lot of trade offs to attempt to optimize.
Exactly, I was just about commenting the same. The heat exchange between the piping and the environment is happening through the piping wall, and that surface area has no squared parts in the equotation. That is a wrong statement in the (otherwise very good) video.
It can get very complicated very quickly, when you consider material types, thermal conductivity of those materials, surface condition of those materials, the differential of temperature between the inside and the outside, and how tightly the bends are in that tubing where there are corners. So much of it is kept simplistic and generalized because the minutia isn't worth considering.
First time seeing your videos. Its very clear why you have 1M subscribers. Concise, straight to the point, well educated!
As always a well informed analysis of the situation and made me think about the potential for my Ram Cummins !!
Always super well explain
Thanks for your fantastic work!
This is the chillest person on RUclips and thanks for the video I’m a young enthusiast this helps a lot to understand turbos
Some of these pictures are incredible. I remember reading a bit about STS back in the early days but hadn't paid attention since then. Cool to see.
Thank you for the video and the good job you did in it! 😁
Love your vids man... i learn tons of stuff! 👍
Thanks for this excellent and informative video! You helped me learn about a turbo setup that I didn't previously know existed! Very cool! 😃👍
First of all: Happy New Year!! 🥂
Damn! I don't have a car, I'm not planning to buy one anytime soon and I guess I'll never tune it up for track, BUT I enjoy so much with your videos and I'm always glad to learn something new!
Keep it up! Cheers!
I really enjoy watching your videos man, you speak nothing but facts I actually learned alot from watching your videos and am glad i disscovered your channel😀
This video was perfectly timed! I've been trying to figure out what to do about do about forced induction for my planned swap
Thank you. I have seen them more but had no clue why or the draw backs.
Great vid! Really clear and informative
excellent video. this was a good explination on this type of setup.