Building a stroker out of a 4.0L

[GaryMB]

I have a 1994 4.0L engine out of Jeep Cherokee with about 170,000 miles that I think had overheating problems. I've already pretty much torn the engine down to the block, and am going to do a rebuild and at the same time stroke it with a 258 crank and rods. This is only my second engine rebuild, and my first one where I actually know (somewhat) what I am doing. What I mainly am concerned with is making the engine last, and am unsure as to how detailed a rebuild I need to do to get another 170,000 miles out of this engine. New rings, seals, gaskets, plugs, oil pump, timing kit, and bearings are a no brainer. However, will I 1.) need a remanufactured/ground crank, or will a high mileage crank be reliable? I can buy one at the junk yard for $40 or a crank kit for $220+core. Also, the 2.) cam...There is a machine shop near by that custom makes cams for about $130. It's cheaper than a crane cam, so I think I'll just order a custom made cam designed to work well with the longer stroke while not sacrificing too much reliability. I'll buy new push rods and lifters to go with this. 3.) Do I need to bore the engine and consequently buy new pistons to make it last, and 4.) do I need to replace anything else like the springs or rocker arms? 5.) I am thinking of having the block and head boiled and magnufluxed to check for cracks and clean out the cooling system. I appreciate all the help; hopefully this project will go smoothly and not cost an arm and a leg. Oh and I'm doing a transmission swap at the same time. It's an NV3550 with 2k miles on it.

 

[Snitty]

I say talk to the junkyard and tell them you want a crank that you can go get inspected. Say that if it is bad, you'll want your money back. Some places will, some won't. A used crank CAN be just fine. I would suggest at LEAST honing the cylinders, but I would seriously suggest getting it bored .030". You can order a complete engine kit for a 4.0 which should have everything you need from a parts store for around 500 bucks. The 258 (I believe) uses the same bearings and everything so that should work great. Call crane and tell them what you are looking to do. They will suggest a specific cam, ask them for all the specs so you can get one ground at a better price. You'll likely want some 24# injectors. I read that a mustang is a good donor for that. Rocker arms should be fine as they are. Springs MAY be ok, but should be replaced if you have that many miles and plan on making it last. Valve seals might come with an engine kit and are probably a REALLY good idea to replace. While changing seals, you might as well have the valves checked over well.

If you get an engine kit, it should include pistons. I think you can order them with overbore pistons. If you want some extra power, you can order high compression pistons. But with it being a stroker, you're going to have higher compression anyway. I think it comes out to about 9.5:1 with a .030 overbore. You are looking at using about 89 octane what that sort of ratio to make sure there is no ping. If you go with high compression pistons, you'll likely be looking into the 10:1 range and you'll probably be want to use 91 octane.

another way to get more power, you can add more compression by having the head shaved slightly if/when you get it boiled or decked. But a more logical approach would be to get the block shaved. The stroker has a lower quench height than the stock 4.0... the piston actually never reaches the top of the block at TDC so you will have room to shave there.

Since you will be working with a higher compression, you may want to look into a better cooling system. The longer stroke (which is what raised the compression in the first place) also creates more heat because of the more metal/metal friction. A good oil, changed regularly will help keep temperatures down as well.

The stroker is JUST getting in the range of requiring a better fan. I see you have the taurus fan which might work fine. But once you get into larger cubes, it takes more air to cool the motor, you might want a secondary pusher fan or TRY to alter the electric to push and put the clutch fan back on. I could be going overboard with that, but its not a bad idea.

 

[GaryMB]

RE: Jeep Trailor???

Wow, that just about answers all my questions. Thanks, Snitty! One more question though...Is it OK to use a spacer on the crankshaft to allow the serpentine balancer to fit, or is it a better idea to shop around for a crank with a shorter snout for the serpentine pulley? If the spacer method is fine, how would I make one that wouldn't off-balance the whole rotating assembly? Oh, and will high compression hurt my low-end torque?

 

[Snitty]

RE: Jeep Trailor???

Higher compression will not hurt your torque. You're going to have well more than you need. If you want, an inertia ring would not be a bad idea. I've heard a lot of good things about those.

As for the crank. You can use a spacer, I've seen a lot of articles where that was done, but I'm not sure how to go about aligning the rest up to it. You can also get the end of the crank machined down to accomodate for a serp

any more ?s, ask away

 

[GaryMB]

RE: Jeep Trailor???

Well I've been doing research up the wazoo. So it seems that increased quench height and increased compression lower engine reliability from primarily detonation, while increased compression has a direct correlation to increased horsepower and efficiency. I can live with a 9.5:1 CR with an overbore and new cam. However, the quench and compression ratios for the various engine combos at this website worry me: http://www.jeep4.0performance.4mg.com/photo3.html I read at this website http://www.speedomotive.com/Building Tips.htm that a factory quench height is somewhere around .035", and anything above .080" defeats the purpose of a quench style head. A simple stroker looks like it will have more than .080" in quench height. I've always been told by mechanics that the stock setup is what is reliable...to mantain the reliability and low emissions of the stock motor, do I need to deck the block to return the quench height to stock and purchase dished pistons to lower compression so that detonation is not experienced? Or is it not that big of a deal?

 

[GaryMB]

RE: herculiner

Oh and the stud that holds the dip stick tube in the block won't unscrew. Will it screw anything up to drill it out this close to the top of the block?

 

[Snitty]

Welp, as far as quench, you CAN get the block decked, but that will increase the compression to about 9.9:1 (with a .030" overbore). That will give you more of an issue for detonation. But I don't think you'll have a real problem with pre-ignition until you get up into the 10.5-11:1 range. 10.5:1 can easily run on 93 octane fuel. Also instead of decking the block, you may want to look into a thinner head gasket, it will have the same effect. Plus it can be changed, you can't add height back to the block.

As far as detonation.... if you use higher octane fuel, you will not have a problem with that. You can also retard the ignition somewhat, as long as you are not dealing with pre-ignition. It will ignite the fuel at a safer time as the piston will be on its way back down, while the compression is decreasing. Retarding the ignition can also help with your low end. And since that is what I'm sure you are looking for, that can be a good thing. Then of course I don't know where the stock ignition should be timed, just haven't looked into it. It may NOT be a good idea to put it into a negative. TDC would probably be a good place to have it.

A stroker with no deck mill, .030" pistons, stock gasket, a good cam, and 24# injectors can get you around 250 hp and 300 lb-ft of torque

 

[Junkpile]

New Here 1st jeep need paint ideas

There is a saying that applies well here:
"Fast---Cheap---Reliable.....pick two, because you can't have all three."

10.5:1 compression without detonation? Maybe.....if you had an aluminum head, perfect combustion chambers, and a reeaaally choppy cam.

Do more research, then follow that up with more research.
Call up one of those evil companies that try to push those overpriced stroker kits, and ask them a few questions. I'm not saying buy anything from them, just get the professional opinion. Tell them you want to build a stroker but everyone is telling you that it can be done with junkyard parts and that their kits are a waste of money. Let them give you the other side of the story and then make your own decisions. Most of the kits are based on a 258 crank that you can get alot cheaper elsewhere.

A mismatched combo is even more disappointing on a smaller displacement engine.

As far as durability goes with a stroker, there are no worries. The seven main bearing AMC I6 is beefy on the bottom end. Pay attention to clearances and use quality parts and it will be fine. [/i]

 

[Snitty]

10.5:1 without detonation can be done... but like I said, you're going to want premium fuel and good injectors. The LT1 has such compression, and some of them have iron heads (of course they have a good knock sensor too). I'd really suggest staying under 10:1 though.

when I build a stroker... I believe I'll be going with:
-.030" overbore dished pistons (clean cylinder walls and keep low octane workable compression)
-.030"-.040" deck mill (get proper quench height)
-stock head gasket (cheap and easy to find)
-stock HO head (small intake runners help with low end)
-24# injectors (gotta get enough fuel in there so I don't burn)
-possibly an adjustable FMU
-Custom recommended cam with a good low duration (torque torque torque)
-inertia ring (wonderful device to help keep flywheel momentum)

 

[GaryMB]

As for fast, cheap, reliable...I'm willing pay a little extra for some reliability. It's only an extra $80 to have the block decked, but what I havn't been able to figure out is the price of having the pistons dished. Everyone I have talked to at either auto shops or machine shops all keep mentioning pistons with lower pins whenever I mention dished pistons. This would defeat the purpose of decking the block and set me back to square one with alot less money in my pocket. What exactly is involved in dishing the pistons, i.e. do I just tell the machinist to mill this much out of the dish on the new overbore pistons?

 

[GaryMB]

I've been contemplating this whole stroker thing and how much everything will cost. What I'm wondering now is how much custom pistons will cost. Everything that I am going to paying for that could be avoided with custom pistons is having the block decked, the pistons dished, and purchasing 4.2L rods. If I bought custom pistons, I would be able to reuse the 4.0l rods, regain factory quench specs, and lower compression all with one purchase. ???

 

[Junkpile]

RE: Rear Brakes Leaking

Check out Speed-pro/Sealed power, Keith Black Silvolites, TRW, or call Clifford Performance and ask what piston they recommend. It can be done different ways with creative machining from what I have heard, but some pistons made specifically for the application would solve alot of problems and make things easier to deal with.


Snitty, while I understand the desire to concentrate on the low end performance in a four wheel drive vehicle, it's not really a concern with this engine in this vehicle. Concentrate on improving where improvement is needed, the mid-upper rpm range. You'll wind up with a much more rounded engine that can perform more tasks and will be more fun to drive when not just putting down the trail.

Unless you guys are planning some port work, run a split duration camshaft to help crutch up the slightly inadequate exhaust flow that the HO head has.

 

[Snitty]

I can agree there. The stock 4.0 itself has great low end, as goes with the 4.2. And I can agree with the need of a more rounded engine.

As for getting the pistons dished. I would just buy dished pistons to start with

as for the pistons with lower pins, that will eliminate the need to deck because the piston will sit higher in the cylinder and will not go down as far. The stroke will be the same, so the CR will be the same

 

[GaryMB]

Does anyone know the cylinder head volume, or combustion chamber volume on a .030" overbore with x deck height jeep 4.0l high output engine? I'm trying to figure out the compression ratios with various piston/deck mill combos. Apparently using a mopar performance .043" head gasket will return quench to stock (or does increased displacement require lower quench heights i.e. decking?). I'm thinking of finding a combo of head gasket thickness, deck height, and pre-dished pistons w/o having them dished more and end up with a compression ratio between 8.8:1 and 9.5:1; my mechanic recommended 9:1 as a reliable compression for an engine under load running on pump gas. Here are some possible pistons:
Stock 4.0 cast aluminium '87-'93 #83500251, '94-'95 #4773157, '96-'04 #4798329----1.601" 13.1cc
Keith-Black Silvolite hypereutectic 2229----1.581" 11.5cc
Speed Pro hypereutectic H825CP----1.592" 15.8cc
Speed Pro cast aluminium 677P/677CP----1.585" 17.5cc
And of course I can choose between .051" and .043" head gaskets. Oh and how much does compression affect gas mileage, and how will various compressions and quench heights affect emissions (I'm in CA)?

 

[GaryMB]

Re: Sporatic vibration

Well I'm (hopefully) taking the block and head into the machine shop tomorrow. So far the plan is to have both boiled, get the block bored .030" depending on the cylinder ware, get both block and head magnafluxed or vatted or something of the sort, have alignment of mains checked, and have a valve job done with installation of new springs, valve guides and valve seals. I'm going to check to see how much dishing some aftermarket pistons will cost, and if it is not too much will go ahead and have the block decked .030". From there I will determine the necessary dish volume for the pistons that I select. Right now I am deciding between Keith-Black Silvolite hypereutectic 2229----1.581" 11.5cc because i have heard of people dishing them out to 30cc, and Speed Pro cast aluminium 677P/677CP----1.585" 17.5cc because they already have a bigger dish. My question to help determine the propper piston is this: what is the compression height of a piston, is the difference in compression height between these two pistons alot, and what do you think of modifying the combo:
Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Keith-Black Silvolite UEM-2229 +0.030" bore pistons
Increase piston dish volume to 30cc
8.8:1 CR
Crane #750501 192/204 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar Performance 0.043" head gasket
0.058" quench height
2.25" exhaust
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
231hp @ 4400rpm, 327lbft @ 2000rpm
Into having about a 9.1:1 compression by only decking the block .030", using a stock head gasket, dishing the pistons to less than 30cc, and having a custom cam that is close to the one in the above engine combo but built for a little higher end power? My concern with dishing the pistons this much is if they will still be strong enough to be reliable after this much metal is removed. I've been told that automotive parts rarely have more material or componets than is absolutely necessary.

 

[Snitty]

thats why i say to just buy dished pistons