Jeep® 4.6L Stroker Buildup Versus Stock 4.0L Rebuild
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- Опубликовано: 23 июл 2024
- The Jeep® 4.6L stroker inline six is a popular buildup spurred by ready parts availability and the relatively minor work involved. Time for rebuilding a 1987-2006 inline 4.0L is the usual starting point. In this video, Moses Ludel discusses the merits and "why" adding a 4.2L or Scat aftermarket crankshaft to a 4.0L block makes sense.
There are tuning (mainly an injector upgrade) and other details involved with these buildups although the outward appearance of the engine remains bone stock. For a roster of related articles, review the search list at: www.4wdmechanix.com/?s=4.6L+s.... In these articles, pay particular attention to camshaft choices, tuning measures and the differences between pre- and post-Coil-On-Plug engines (starting with some 1999 models and running through the final 2006 model year). The C-O-P engines require specific camshaft grinds. The wrong camshaft pick will throw an engine check code or cause drivability issues.
The 1991-1999 (distributor equipped) engines are the easiest build, but do not rule out this stroker approach with Renix or C-O-P engines. Discussion around the 4.6L stroker build has moved to the forums. Join us there and search for "4.6L" at: forums.4WDmechanix.com. 
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Thank you for the video. I've been on the fence about a stock rebuild or a low CR 4.6 stroker. I've got my answer now!
Pleased that you found this helpful...
Thanks for the vid
You're very welcome!
Thank you for this video. My son and I will be building a 4.6 L engine using the crankshaft and connecting rods from his 1986 AMC Eagle and an engine from a 1993 Jeep XJ Sahara. What will our approximate compression ratio be? Will we need use a higher octane fuel?
Thanks again.
With stock replacement (dished) pistons, static compression and a stock block deck height, compression will be over 9:1. 8.7:1 to 9:1 is a safe bet for regular fuel. The 1991-99 4.0L heads have a good anti-knock design, and these engines did not need a knock sensor. Your question is warranted, though. You can bring the compression down or in line for lower octane fuel by running a thicker head gasket that will work with your build. There are Cometic gaskets. FelPro is fairly thick. Edelbrock's gasket is thick and designed for a big bore, which should drop compression slightly on a 0.030" standard rebore. If the block and head decks are true, clean surfaces thoroughly and leave them stock without milling/decking. Decking will increase compression. (Always confirm the lifter clearance/preload with your assembled long-block. Use the right length pushrods. A $20 CompCams pushrod length gauge is the ticket here.) I like a stock or milder "RV" camshaft that will provide the best low-end performance. CompCams' older 252 grind was my go-to for decades and worked well for all but the later coil-on-plug 4.0L engines (2000-up, some 1999 engines). If fuel mileage is important, I avoid "bigger" mid-range/higher rpm camshafts with more valve overlap. For bottom end torque and fuel mileage, you want a mild duration cam with more lift to get better manifold vacuum from idle to 4,500 rpm. Some argue that a lower compression 4.6L is a waste of energy and money. It depends on your expectations. If a major improvement in lower rpm torque is the goal, the 4.6L is a must. You have the crankshaft and rods, there's no reason not to do the 4.6L build. Mild builds with a lower rpm ceiling may not require a fuel injector change. Worst case, 302 Ford V8 replacement injectors work.
Thank you, Moses, this is very helpful. Our goal with this car is to be an on-road driver; it’s highly doubtful we’ll take this off-road. We may pull a boat trailer or camper with it. We don’t want a high-RPM engine, but rather a torquer. After a lot of searching and comparing specifications, we purchased a CompCams Xtreme 4X4 206/212 Hydraulic Flat Cam for AMC 199-258/4.0L. According to CompCams, it provides “Excellent torque and throttle response. Great stock cam upgrade in fuel injected applications.” These are the specifications:
Intake: Adv Dur: 250, Dur: 206, Lift: 0.462
Exhaust: Adv Dur: 256, Dur: 212, Lift: 0.478
Lobe Separation: 113.0
The part number is 68-232-4.
How does this compare with the 252 grind?
Our biggest challenge right now is modifying the gas tank to fit an electric fuel pump for the fuel injection system.
Thanks again.
This is a good grind for EFI/MPI. The profile is a duration close to the 252, and lift is ample for low-end torque. Lobe separation looks reasonable. This should work, I like the 800-4800 rpm target. As for an electric fuel pump, the Mopar MPI/EFI conversion kit for the 258 sixes uses an inline fuel pump mounted externally in the fuel system between the tank and engine. Optimal mounting point is near the tank. The 60-way/pin PCM triggers the pump operation as it would an in-tank pump. The external mount pump has been a common Walbro type with the correct pressure range. HESCO and others sell the external fuel pump. This picks up fuel from the stock tank sock and pickup tube. You need to use a return fuel line from the '93 two-rail EFI back to the fuel tank. If the chassis already has a fuel return line, you can tap into that and pick up the return fuel at the pressure regulator's return fuel rail. You're basically doing a Mopar EFI conversion. My 1972-86 Jeep CJ Rebuilder's Manual (Bentley Publishers) and HESCO's website detail this conversion. You have the fuel pressure regulator at the engine with the '93 two-rail system. Later Mopar kits pattern off the TJ Wrangler that used a tank fuel module-mounted pressure regulator and single rail EFI. Stick with the two-rail for your installation. You already have the pressure regulator.
Thank you so much for your comprehensive responses, Moses. I’ve ordered your 1972-86 Jeep CJ Rebuilder’s Manual.
It would be MUCH easier to use an external fuel pump, but I’ve always heard that they only last 2 - 3 years, while the internal pumps last much longer due to being cooled by the fuel. Reliability is a very important factor for this car. The source of the external pump Hesco is selling isn’t revealed, and they’ve added “The actual pump may vary from picture due to the original being discontinued by the manufacturer” to their description. Can you recommend a good, reliable external fuel pump for this engine?
Thanks for your interest in the Jeep CJ Rebuilder's Manual...There are a number of quality pump suppliers for external pumps. I would look at the Summit Racing website offerings for ideas and reviews. The critical issue here is a supply pump in the same pressure range and volume as the OEM pump for a '93 YJ Wrangler. Walbro has been an aftermarket supplier of OEM caliber pumps for the in-tank modules. They use the GSS340/341/342 for a '93 Wrangler OEM replacement application, which is a 255LPH (liters per hour) flow and a maximum 500 horsepower. The stock 1993 in-tank fuel pump reaches a maximum pressure around 75 psi and is able to sustain 39-41 psi at the fuel rail test port when the engine is cold (during cold start warm-up/enrichment). When warmed and idling, pressure should be approximately 31 psi at your fuel rail test port. This is not a huge demand for an EFI-type fuel pump. You must have an unrestricted fuel return line to the fuel tank as I have noted. The line should be 5/16" minimum on the return side. 3/8" double-flare brake/fuel tubing works well on the pressure side, I run it the length of the frame and use high pressure EFI hose at the flexible ends. (I bubble flare the tubing ends and use EFI-type hose clamps, details covered in the book you ordered.) Here's a less expensive universal Walbro pump at Summit Racing. There are wiring and external mounting kits shown at the same page: www.summitracing.com/parts/vpn-gsl392bx. Keep in mind that the fuel pump gets triggered by the PCM. The pump is not switched on and left on. A wiring diagram and OEM shop manual provides details on how to wiring up the fuel pump. (HESCO has an EFI conversion PDF download that's helpful, too.) For wiring diagrams and troubleshooting, I highly recommend a CD factory shop manual, available at eBay. Here's a good buy on a Bishko licensed FSM specifically for your EFI system: www.ebay.com/itm/233825069149. As for reliability of external pumps, that's a reasonable concern. We towed a stranded V8 conversion Jeep TJ ten miles out of the Moab backcountry with a failed external electric fuel pump. Suggestion: Carry a spare pump and the tools/know-how to replace it.
I would say that for a daily driver setup I would stay with a good 4.0 build unless you like filling up with premium fuel which a stroker build will almost always demand.
This is why I hold to 8:1 or 8.5:1 (maximum) compression on my builds. You may need the higher flow injectors for higher rpm. (I hold to a maximum 4,500 rpm and seldom get near that speed.) Unleaded regular is acceptable with a mild or stock camshaft, especially at 8:1 compression. I'm taking advantage of the low-end torque available from the longer stroke, which also works well for running tall axle gearing if fuel mileage is a concern.
@@RoadReadywithMosesLudel Good to know you can take advantage of the extra cubes and run regular.
@RoadReadywithMosesLudel doesn't staying at or below 4000rpm, have the.stroker producing very similar power to the stock 4.0?
All the dynos I've seem, show the strikers to not really make a difference until nearing 5000rpm
Dyne results are usually with engines beyond 9:1 compression and with a "bigger" camshaft like a 260-degree or longer duration camshaft. A camshaft of this duration will have more valve overlap and poorer performance down low. (Lower manifold vacuum at lower rpm is a good indicator.) If we compare a stock bore/stroke 4.0L with a stroker at 8.5 or 8.7:1 compression, each with a stock or mild duration camshaft, I am certain that the 4.6L will produce more torque and horsepower from idle to 4,000 rpm. The 4.0L is an over-square design with a larger bore than the 258 six. The stroke is much shorter. This leads to less bottom end power and the need to wind the engine up to reach its torque peak. '80s emissions laden 4.2L/258 AMC/Jeep inline sixes were designed for bottom end torque: the torque peaks as low as 1,600 rpm. This is a torque rise similar to a diesel engine. The 242/4.0L cannot, by design, produce a torque rise like this, the stock engine requires rpm to produce peak torque and horsepower. If we we're talking about fuel efficiency, I would like to see a comparison of a stroker 4.6L running modest compression and either a stock 4.0L camshaft or a shorter duration, higher valve lift camshaft. (My historic favorite 252 CompCams grind for pre-C.O.P. engines is one example and a choice I would make. The 4.6L would breathe a bit better and produce higher manifold vacuum at an idle and lower rpm.) For trail running and city traffic, this is the kind of build I would want. Foot lighter on the throttle, the torque with a heavy flywheel would be great for off-pavement crawling. The cost of building a 4.6L is nearly identical to a thorough 4.0L rebuild once you have a 4.2L/258 crankshaft.
I just like big inline-6's 🤷
I do, too! Easier to balance, inherently smoother, live a long time, simpler to service and highly reliable. What's more? Even vintage four-main bearing sixes like Chevrolet, GMC, I-H, Chrysler's slant-six and Toyota F-engines stay together well. More modern seven-main bearing sixes are that much stronger.
@@RoadReadywithMosesLudel What's weird to me is some of the outright hate for the 4.6 or even the 4.5 "poor man's stroker". When I had my 4Runner I mentioned briefly on the forums I was gonna sell it and build a 4.6 in it's place and I got a dozen people immediately saying I'm a fool for choosing that when I could spend the same amount of money on a full 3.4 rebuild, adding a supercharger, smaller pulley, 7th injector, piggyback ECU with dyno tuning and methanol injection - and still make less power in the end 😂 Even on the Jeep forums you find some people that spread BS on how you "hardly gain anything" from it and it's not worth the time, and often act like if you do anything to a stock 4.0 and/or do anything but LS swap then it's gonna blow up and everyone will die and your wife will leave you. Super weird.
These engines have a lot to give if you tinker with them - they always have, even since the CJ days. If I'm not mistaken my dad has a 4.0 head on his 258 (CJ7) and it was the best money he ever spent
There is room for V8 swaps, but the 4.6L rebuild is very sensible. With a 258 crankshaft and possibly a set of higher flow injectors (depending on the build), the cost to machine and assemble a 4.6L is otherwise the same as rebuilding a 4.0L without stroking it. The weakness of the 4.0L is the shorter stroke that negates the bottom end torque. A major advantage of longer stroke inline sixes is stump pulling power down low. 4.6L dimensions actually follow a fifties/sixties light and medium duty truck engine performance strategy. (The 4.6L stroker reminds me of the 292 Chevy/GMC and 300 cubic inch Ford inline seven-main bearing sixes. Not the best fuel mileage but more low-end torque than an equivalent V8.) The result is reliability, ease of balance and gobs of bottom-end torque. The iron inline sixes are not the most fuel efficient, but they're virtually indestructible. If a Jeep owner wants higher rpm power, a GM LS V8 is more efficient. (Stroker 4.6L inline sixes with a "big camshaft" and boosted compression become a toss-up. Here, I would opt for an LS V8 for fuel efficiency.) Crawling around on the rocks, I'll take the low-end inline six-cylinder torque and a weighty flywheel. If a daily driver or freeway flier, I would consider an LS V8 like the 4.8L or 5.3L. One place where an LS would also be my pick would be meeting emissions requirements. At my magazine's forums, CJ and YJ 4.2L owners hit the wall trying to restore the emissions system or upgrade to expensive 50-state legal EFI to remain emission compliant. Here, a stock appearing 1991-95 4.0L or 4.6L emission compliant inline six conversion or a clean 50-State legal LS V8 swap makes sense to me.