Calculating Compression on MOPAR 383
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- Опубликовано: 10 сен 2024
- Nick's Garage Gear Shop
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Nick knows that the right compression numbers are critical to making good power. Today, he will show you how he calculates the compression in this classic 383 Mopar.
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Geez Nick, freely giving away decades of knowledge like that. I just don't see that very often. Thank you so much. You are the greatest
He's a natural teacher.
This stuff is common knowledge
@@williamarnett9064 when I go to buy a head gasket for a 440, it's going to be the one Nick says.
Nick if you have a problem getting the right Pistons isn't there a way you can offset cut the crankshaft and give the motor a little more stroke? .075 below the deck wow.
Amen
This is very valuable to people just beginning in their Hot Rod career and a good review for us who have been around for some time. Many times the simple things like this can make a huge upgrade in performance. Getting the right pistons and head gaskets can make all the difference in the world.
I recently explained this to my cousin when he was building a 455 Pontiac engine.
He was going to use some large CC chamber heads on his build that would have resulted in a CR of 8 to 1.
He sourced another set of heads for a CR of 9.5 to 1.
I really enjoyed watching this video about calculating compression ratio. When I first saw the video on the Road Runner I knew it was down on power, and probably compression, but I had no idea that it would be this low. After Nick finds the right piston, and zero decks the block, I'm sure that this 383 will have all of it's power back, and then some. 400 HP will make this RR a very nice street machine. Great job on the video George, very informative, and entertaining. I always enjoy these learning videos, keep them coming.
Thank you for your kind comment, Eugene. We know there was one (yellow) thing missing from the content this week. 😉
Nick is always sharing technical specs that's why Nick's Garage always gets my respects Holler holler Eugene!
@@NicksGarage I saw a few peeks of yellow in the background, so that's enough to satisfy my yellow fix, until the next video.
Can;t wait for that one then will be special!
Hi Eugene. Looking forward to the day they fire up your car!
030-.040" quench is good for power and helping prevent detonation. Zero deck with valve relief flat top pistons and .040" head gasket. Dynamic compression/ cranking compression is where the camshaft and real magic happens
Yes, depending on camshaft profile.
I remember reading somewhere that the old guys would say just before the pistons "slap the heads" is where you get the best power! When the pistons come up to TDC the mixture is forced out of the quench area into the center cavity increasing the turbulence, like vortec heads, increasing the burn rate and power. They discontinued this because it increased emissions! They used to have two quench areas then one then open chamber for emissions.
Most "rebuilder" pistons are destroked about .040. They do that so that the rebuilder can mill the heads, bore the block and even deck the block and the compression ratio will stay at or be below the factory specs. It makes it so the rebuilder has less issues with piston failures from the compression getting higher than stock and the customer using low octane fuel, maybe too much timing and a cooling system that might be less than perfect. They don't care about performance. If you use those pistons on a engine that everything else is stock you get the situation Nick found on the 383. Good aftermarket performance pistons should have the original pin height.
This is exactly what I have found to be true of most "rebuilder" pistons. Most are in the range of. 040 below deck.
Bonus episode is much appreciated. Good information to help a novice like me understand why my engine is so sluggish. I knew in general, but not all the specific details.
As well here
30 years ago i built my first engine. Everything was done by the numbers from the engine shop. And a little 350 gm small block with 8.5 to 1 became 10.5 to one. Bored .60 over. Raised flat top pistons to match the 202 heads. Gutless wonder became big power. Which need new trans built to handle it all.
Wow. You built an engine that was .600 over! 😂
And this is why I want Nick to build my 340. (& everyone else too)
Wow!!! This, like all the other instructional/build videos, was fantastic!! Compression ratio is something all gearheads talk about but few know how to figure/calculate it. Nick, EXCELLENT job of explaining it and what can affect it. This gives some great tips on engine configuration for diy builders. George, great work on your production!!! See y’all Friday night!! 😊
Dr. Nick, this is why I watch this channel, you explain everything of what you are doing, and I can not wait to see this 383 reach 400 hp, cheers.
I love to watch a true master at work
Good morning Nick and George, wow it's Wednesday, and another episode of Nick's Garage, awesome!
Morning! As Monday's vid was a bit shorter than usual this week, we managed to get a bonus episode put together. Hope you like it!
Good morning to the state of Texas, hope all is well with you.
@@NicksGarage WE did like it.
@@derekbowbrick6233 Good morning Derek, everything is good here, hope you are doing ok too.
Great video Nick I loved it reminds me of when I was 18 years old I read my direct connection book from front cover for a year and then I had the Machine Shop do all the 0dec and clean the head up so it was good and perfect yeah I no doubt I cannot believe I mean I'm 63 now I can't believe hardly that back then I was doing 1101 at 120 miles an hour people couldn't believe that Dodge all I love that 440 thank you Nick
Good morning Nick: Your knowledge is a "treasure" for the car community. I subscribe because it bridges for me, what i grew up on "muscle cars" with current era versions of that. Great video👍
Should be called « Professor Nick’s Garage », you are number one !!
Nick did this same process for me when I worked on my block. He walked me through just like this, and shared many tips and tricks. Why make the drive to see Nicks Garage? Because he’s worth it!
Just a superior tutorial on calculating compression ratio and it's relationship to power production. Nick is a REAL master engine builder! Thank you Nick you're the best. I can't wait to see the 383 on the dyno when complete...
Yes for sure
Great video and something that people sometimes just ignore when they go to build or rebuild an engine. Then they go get a big cam and throw in something and the compression ratio is way below what the cam wants and the engine runs like a 3 legged dog.
I've been going through this on the Cleveland I'm rebuilding because it is around 8.5:1 right now.
I’m so glad I came across this channel after purchasing my 71 D100 with a 383. Just wish I lived closer to him. I’d quit my job to work beside Nick!
Thanks Mike!
That’s a beautiful car. It’s interesting to see compression test. That’s the heart of the motor. Nick is great at explaining how motor tolerances work . Thanks.
Nick, I struggle each day with depression and anxiety and suicidal thoughts. Your videos keep my mind occupied in a way that I don't dwell on the struggles of my life. Thank you Nick and Crew.
Thanks for sharing. We understand your struggle, and we’re honored and touched that we can be some help. 👍
This is probaly why my 1972 chevelle ss with a old truck motor 454 outran my buddys 1970 roadrunner 383 with 4 speed, not sure what gears chevelle had or his but his car had to be slow, the, chevelle had 400 turbo auto and best quarter mile time was 14.7 , great job great show guys!
what very important is quench what most engine builder dont talk about i like between 0.25 and 0.35 quench thank you nick very good video
A very good quench prevents detonation.
Great stuff, "all killer, no filler!"
Would definitely like to see more concentrated technical videos like this one.
DR Nick fixes the patient with no energy and will turn it into a tough guy on the street
Thanks, G&C. That is the plan!
Yes! it's so good to see you explain this for people excellent content you guys rock.
Our pleasure!
I have a 383 in my Coronet. It is a slug. Watching this confirms all my rebuild mistakes.
The more I watch your videos the more I learn and I have owned a few mopars over the years in fact my first car was a 72charger 318car but I loved the way it looked I am glad I found your videos helped me keep my sanity while I was laid up after rolling my jeep down the highway love mopars and y'all don't bash other brands
Glad we could help.. and we hope you are doing much better after the crash.
In all my years of wrenching on vehicles I've never done more than basic compression as well as leak down tests etc. Thanks Nick for a very informative break down on calculating compression ratios. YOU ROCK DUDE! 👍 ✌️
Back in the old days; we had to calculate the volumes on paper to figure out the CR.
No online calculators in those days.
Kind of feel bad for the person who did the original rebuild, thinking that they increased power, only to find it had less power. Thanks for the heads-up info and sharing your knowledge!
More good advice, He learned the hard way, We all need to say thank you Nick for our projects and doing it Right the First time
I built a 383 years ago and used Keith Black pistons (with one large valve relief trough) which were .030 below the deck, then milled the block AND the closed chamber heads AND a Cometic .030 gasket to finally get to an honest 10-1 comp. ratio lol. All these years later I’m still hearing that the aftermarket is still not very kind to the 383 for building compression.
Outstanding episode, THANK YOU!
Thanks n6mz. Glad you enjoyed.
You can also calculate the effective CR on a built engine based on the cylinder pressure:
CR(effective) = CylinderPressure - AtmosphericPressure)/AtmosphericPressure
For example, if the CylinderPressure is 160 psi and assuming AtmosphericPressure is 14.7 psi, then
CR9Effective = (160-14.7)/14.7
= 9.88
Great info. Thanks.
Wow. Licensed mechanic here. Did not realize this. Thank you.
Of course 14.7 psi is average atmospheric pressure at sea level. You can get the approximate atmospheric pressure at your location/elevation from the weather service but it will be in millibars. So, 1.0 millibar = 0.0145 psi
Good Morning Nick & George, thanks for informing us as to why that 383 didn't have any power. Very interesting as is how you measure the correct compression ratio. Top wee video thanks and stay safe all.
Effective compression ratio can be different, according to the camshaft.
He was just stating stating the basics. I'm sure he can do a whole other video on static versus dynamic compression. He was dumbing it down for the average Joe.
@@bradleynelson5915 That is correct. Thank you.
Yeah, the DYNAMIC compression is greatly affected by the duration and LSA. That's why cams like the Comp Thumpr, Howards Rattler, and Hughes Whiplash cams have lobe centers of 107 to 109, and close the intake valve early; to build cylinder pressure on low static compression engines. But a restoration guy won't like the choppy idle and low vacuum.
Thank you Nick! Do more videos like this!
Look forward to seeing more educational videos like this! Real entertainment!
Nick you remind me of American physicist Professor Julius Sumner Miller because he would explain why and how things worked and here you are explaining the physics of compression ratios that apply to all internal combustion piston engines. This is valuable and useful. Thank you.
Now that was a GREAT Video!! More like this, Thanks Nick
Thanks for the lesson Nick. That's what happened to me, I had a 1980 351w built, 30 over and a bunch of stuff done to the engine, I wanted between 9.5-10:1 compression, I got it back assembled, put it in a 1980 bronco but always felt that it was very sluggish, fast forward years later I gave the engine to my friend Tony to build it and put it in his Cougar, when he pulled the heads off, the pistons sat down in the cylinder, exactly what Nick just explained, I think my compression was only about 7.5-8.0:1 compression, no wonder I had no power, but now after a full rebuilt done right,Tony is running 500plus HP. So if you get your engine built, find someone who knows his stuff and understands what your after!
Awesome! Everyone have a seat, be quiet, pay attention a take notes. Class is in session. Professor Nick is lecturing.
We need more short episodes like this .
Really interesting, thanks Nick for showing us 👍😁
Glad you enjoyed it Dave.
Merci/ Thank-you, really nice to have a mid week video. I remember having a formula from school, and the one that showed you tire size and engine rotation for your true speed.
You're very welcome!
Great show Nick...would like more of these tutorial type videos
Noted! Glad you like them.
I've spec. a big block Ford 351 c. with 30 over to 10.5 compression . it pumped real good with a mild RV cam . It worked real good! We did allow the machine shop do the lower end line bore crank and cam. They also balanced and decked the block to matched the gaskets and pistons. Wow it had so much low end we had to put wide track tires to hold traction. It pays to trust your machine shop.
We were a more general type shop, leave the critical measurements to someone who is used to this type of exact measurements. There is nothing against you (with all of your experience) this is a money and time saver for us all not so familiar with these critical measurements.
Find a machine shop that is qualified to the that has the reputation and you can communicate your ideas. It will pay off in many ways that most people don't realize.
Nick you've obviously been there, done that, many times. A lot of people watch videos but don't realize that you have to have the skill to do this kind of critical measurements.
Love every one of your videos I've watched. You are a knowledge resource that many rely on.
Just like I was back in shop class!! Awesome that was 45 years ago
good tutorial Nick! This makes it very easy to understand and measure! Thanks!
Hey Nick even though I know this I still found it interesting after all my years as a Diesel Fitter. Very nicely explained for the those that don't know.
Nick,
Great video - thank you! I ran your numbers on two different online CR calculators and they both came up with 7.85:1 / 7.88:1.
Bore: 4.28, Stroke 3.375, Deck: .075/.073, Head gasket thickness: .044, Head gasket bore diameter: 4.415, Chamber volume: 88cc
Paul (in MA)
Really ? With a flat top piston. Which calculator on line ? Less then what I calculated of 8.2. WOW.
@@nickpanaritis4122 I used UEM Pistons and Summit Racing calculators. The Summit one does not include head gasket diameter so it is probably a little less accurate.
Paul (in MA)
@@Paul1958R Thanks.
Hi Nick, I really love your videos! I went to school for auto mechanics nearly 35 years ago and we learned how to calculate compression ratio along with a lot of other things. I sat down and did the math for fun. The hardest part is converting CCs of the head to cubic inches so all the units are the same. It works out to be 5.37 cubic inches. The rest of the math is straightforward and I come up with 7.817:1 compression ratio. What did I miss? Again I love your videos watch them all the time and greetings from Michigan USA. Farmer Bob
I got 7.86:1 and that wasn't even accounting for the extra volume added by the slightly larger head gasket bore size. That probably added another 3-4cc's of volume. So, in reality, it's probably closer to 7.65:1... YIKES!
Hi farmer bob. I also came up with 7.8 ratio. With a .020 gasket and zero deck height he will have near exactly 9.5 ratio when he is done. I used a crude setup with a 60 cc cow syringe and a plexiglass plate with a hole to measure things way back when.
Great Episode....thanks for making it. Very professional tutorial.
11:15 Great point about finding tall CH pistons to limit decking. Plus, the more you deck the block, the less well the intake manifold will line up.
This is great, I'm so glad piston companies will tell you their CH. Some companies openly brag "We have -.010 to -.020" to compensate for decking.
14:05 I always wondered about how to get good head gasket sealing when an engine was not designed with aluminum heads. I'm glad just ordering a Fel Pro does the job.
I was not expecting a little over 8:1 due to the various rebuild parts. Interesting story.
This is GREAT! Two videos in one week! Good morning Nick and Crew! Bill from Linglestown Pennsylvania
Hope you enjoyed it!
I took a "wild" guess at the compression ratio before you showed it and guessed 8.4:1 Steel shim head gaskets were the 2nd thing to come to mind. It seems we grew up with the same "Direct Connection" Bible.
Would have been interesting to see this engine on the dyne in low compression mode for a comparison to when it's rebuilt.
I agree. But I wish I had more time on my hands. 24 HRS in a day is not enough.
@@nickpanaritis4122 Of course. You're a busy guy.
Thanks for the great tech video Nick.
Nick. Thanks so much for the great tutorial on piston compression. You made it so easy to understand even for a novice like me. I'll put that knowledge away in the back of the brain for future reference. Live your show. Love Mopars
Wow what an amazing video! I never realised the math and measurement requirements that are needed to accomplish the job. I worked in meteorology for many decades and I have just been schooled. Thank you very much appreciated!
Sorry but meteorology is all math and physics which is why I say I got schooled big time.
Nick It seems we had this conversation about compression 20 years ago. So I just ran your numbers through the calculator again, They still wont come up with advertised comp ratio. You are right in bringing up the deck height to 0 and giving it a little bit of overbore. However with a flat top piston and .010 in the hole .your lucky to get 9.1 or 2. Add a small dome and get er up there
And this is why I LOVE Nick's garage.....thank you Nick 💯😎
Awesome dial indicator stand!
Not only will the compression be really low, but the squish will not be happening…
Great video, Nick! You covered it all here. Nobody ever talks about the bore diameter of the head gaskets as being a factor, but you did. Thank you.
Thanks Nick for the head gasket part number that looks like a real good gasket for the job.
Good morning Nick and crew from mid Tn. You know your day is good when you a Notification from Nick's Garage.
Good Morning Nick and Crew! Hope you all have a wonderful day! Thanks for sharing your knowledge with us all nick! Appreciate you!
Good morning! Thanks for watching, John.
Thank you nick !! , you’ve probably explained why my 383Hp is as flat as Kansas !! , needles to say when the heads come off I’ll be checking
Thank you for sharing your knowledge Nick! This is helpful. Thank you 👍
Thank You Nick, I am sure that is why my rebuilt 383 was not that powerful, I just love Nick playing scientist, after all, engines are math, and Nick gets it, well done sir.
This is the most over looked loss of power. Thanks for the review Nick you made it simple and complete.
Nick! You’re the grandmaster of mopar.. give Vascili my best wishes for his new life chapter, from the other bow tie guy..
Thanks Bullast.. we will tell him you said hello.
Nick i love how u teach as well as dyno
Very good explanation ! I'm a mechanic and know this , but always good to brush up !!
I don't remember the specs on that iskenderian Cam that I had in my 440 Nick but I wish I could there was great I was one proud happy 18 year old it was cool when people who drove in my car when I nailed it their head would hit the backrest
It's all mythology to me. Nick is omnipotent. X
Amen brother, a lot a great engine builders forget their deck heights... never forget your deck heights!
Good morning Nick I just want to tell you that 440 source in Las Vegas has the 383 stroker kits in stock now.. you can make it at 438 or 496. But they got the kits in stock now..👍✌️💪😉 but just remember because I built a lot of these engines.if you build the 438/.025 piston to deck, Rod ratio of 1.8 ..it'll be 10.5 compression, if you build the 496/.002, piston the deck. Rod ratio of 1.54.. it can be anywhere from 11.00 to 12.00 to 1. Depending on the combustion chambers of the 906 heads/and how much squish that you want.. and on either engine I always shoot for .040 piston head... 😉💪✌️
Thank you for the info.
@@nickpanaritis4122 👍😇🤗
I wish my trade school teachers made as much sense as you do. Cheers.
Would be nice to have the pistons extra tall and deck them instead of the block. I always hate taking material off a block if I don't have to.
Then the piston crown strength would be compromised....best to get the highest pin bore to piston crown height and be 0.01/0.02" down the hole at tdc...not 0.075"
Great video Mr. Nick! Very informative! Thanks 👍
Glad you liked it!
Good video. There are a few more things to consider in the build process or even before taking your project to a builder.
* Having a (older) Block align honed will ensure that the crank centerline will index when time to measure Compression Height (CH)
* Find a builder that has a BHJ fixture for your application to Square Deck your Block or knows the "Old School method" to do it.
* Reconditioned Factory Rods will be different lengths because their caps were cut before honing, resulting in a shorter length.
* CC Combustion Chambers after Heads are completely rebuilt. VJ will sink the valves, porting, and surfacing decks will both increase and decrease Chamber size.
* Try to use a Head gasket that has the exact Bore diameter as your Block's bore. A larger diameter gasket bore will lower CR.
* A deck surface with as much as .004 inch warp will lead to a loss of CR. Deck surfaces as little as possible to correct.
* (For Mopars) For every .010 inch decked of surface, .0095 inch should be removed on the Intake side. That is, either the Intake side of the Head or the Intake manifold itself.
Some people will say these precautions are unnecessary. Maybe so, if you plan to build a cruiser.
Thank You, Nick! I learn something every time I watch one of your videos. You're the MOPAR Master!!!
lt's always good to see you Nick👀 on my PC screen🤩......Thanks my young friend lol🥰👍
Once again Nick,very good informative show. This info is for all engines& there builders. Spoken plainly so even beginners can benefit from it. Greating from South Carolina, Gino
Dam nick sounds like a 84 350 with 265 horse power, my uncle had a 68 charger ! Black paint.
I was just over 4 and remember it smoking the tires.
Oh buy the way one beautiful car
Nick of Nicks Garage gentleman/genius !!! What a master of the HorsePower !! Best Muscle Car man on You tube thnx A1000000 Nick
Wow! Nick teaches a master class. You really know your stuff Nick. Fab video.👍👍
thanks, Now I know why my 383 mag had low power after a rebuild. I always wondered. Too bad for me I sold it. Thanks again
Nick,if this was taught in high school auto there would be a generation of much better mec/engine building.
Canadian here. (Ontario)
Three "years" of mechanic school. (two months of classroom each year, 10 months of normal work)
We learn everything he says in great detail.
@@tsumacity mechanics school yes,I referred to high school
Thank You Nick! As always a great video, you are a Good Teacher!
Excellent lecture by Professor Nick. Thank you for the video and sharing your knowledge.
Low power could mean low compression You gotta check the distance between the pistons and the deck is Nicks first suggestion There's a few things to take into account if compression is to be measured by an accurate amount Next Nick is checking the cylinder head for the volume of the chamber to get an idea of this engines behaviour Bore size, piston stroke, head gasket bore diameter, A bonus Nick's Garage episode not much makes me happier If you think your compression is of a low persuasion You too can find out using this handy Nick's Garage equation
Good Detailed explanation and teaching like always!
ThankYou Nick👍🏻👍🏻👍🏻
using a stock head gasket the motor would have a Compression ration of 8.12 (I see you had the input for gasket thickness as 0.020). With the 0.044 thick gasket that motor only had a compression ratio of 7.8 to 1
YUCK 1940s compression
Good catch.
@@NZMOPAR And late 70s.
@@jeffrykopis5468 yes very true
Wow Nick. We know that when you started building engines you did this work on paper.. (I'm 67 so I know) that was awesome.. great video.
great 4 corner decking review on this mopar 383 . About SBC . . . yeah most aftermarket chevy 'on the shelf' pistons are designed for zero decked chevy = 9.000" decks, stock on many SBC is 9.025" so we take off .025" or 25 thou for that on small block chev's decks with some strokers or destrokers or builds at zero or slightly above deck surface then get quench to .040" usually accomplished with a .040" compressed thickness gasket although can go .039 or .038" if all forged. some go closer but that is a full contact sport LoL ! If the pistons come out of the block oh say .002 or .005 then we are looking at a .040 through .045" gasket compressed thickness .on SBC i choose a non hollow top piston with slightly less cc relief than i need so changes to the head and piston cc i make shall all come to final number planned in the pre-blueprint i take a few cc off a piston rounding corners and sharp edges on the reliefs and or reverse domes shapes and shape mod the chambers. then a build finished blue print is accomplished through the process of building it. i love this stuff thanks Nick ! This is going to be a great 383 ! you could get a custom piston that is taller, your deck is nice and level for it. maybe a rod , crank , piston combo that measures up to zero, have the crank offset ground to make up the difference for an aftermarket off the shelf piston or the pistons and rods that are in there. This is to help everyone out there and nick has the goods. thanks nick.
the computer calculator has a variable you did not discuss. The ratio is between the volume of the cylinder at top dead center and the volume at bottom dead center. The calculations you did is the volume that has to be added to the actual volume of the cylinder.
Good point.
Good on you Nick all the best from Melbourne Australia