Jeep Strokers

I believe I've pinned down my hot running engine to a flat cam. With that in mind I am putting together a plan to get it back up and running. I've had a head sitting in my shop for 14 years waiting for me to get it over to a shop for a little clean up and this seems like a great opportunity to do that along with replacing the cam. My end goal is an engine that I can drive 75 mph on 35-37" rubber and not feel like its wheezing. I live at 6000' MSL and regularly go to the mountains where I'll be up to 12,000 without too much trouble. When I go to the hills I have a small trailer (1,000-1200 lbs) that hauls my gear so the family can ride along.

Here are my engine specs for the lower end

Stock 4.0L block from 91-ish YJ bored .030" over
258 crank and rods from 83 CJ-7
.030 over 4.0 pistons

I'd spoke to a local machine shop who has built a fair number of strokers (he actually steered me to checking out the cam after I described my overheating). He suggested 1.60 magnum exhaust valves, stock intake valves, and very conservative cleanup of ports/bowls/combustion chamber. Thoughts on this approach?

I believe I assembled the engine with a stock head gasket. The piston/rod/block combo I have puts the piston .0225" lower in the cylinder than stock, so the quench is not ideal. The engine has run fine all these years on premium fuel. Summit sells a gasket that they claim is .040". Is there any benefit to trying to gain this .011" back in quench at this point or just keep running what I have?

The machine shop suggest a multi-layer gasket and perhaps a bit thicker one since I won't have the block out to be checked for flatness. Maybe even utilize head studs to put the fear of god in it and get a real good squeeze. Thoughts?

I'm leaning towards the molar performance cams just because I've gone through 2 in this jeep in 105K miles. I'm leaning towards the 229 but I'm open to discussing others. Any suggestions?

I'm leaning towards the molar cam for reliability, but I'm not opposed to more lift. Would this cam with 1.7:1 rockers be appropriate in my engine?

I have a cloyes double roller timing set thats been on my shelf forever for this engine. Any benefit to advancing the timing of the 229 a bit in my build?

Thanks for your input!

1. Pocket-porting the head would be a good idea but I suggest you stick with the stock sized valves.
2. A 0.040" head gasket would be a good idea.
3. You can use the Mopar 29 cam but I suggest you stick to 1.6 ratio rockers in order to be able to use the stock valve springs.
4. With the aforementioned cam, the Cloyes timing set will bolt straight on. The Mopar 29 cam will provide ample low rpm torque without advancing it so you can install it straight up.

Cheromaniac wrote:1. Pocket-porting the head would be a good idea but I suggest you stick with the stock sized valves.
2. A 0.040" head gasket would be a good idea.
3. You can use the Mopar 29 cam but I suggest you stick to 1.6 ratio rockers in order to be able to use the stock valve springs.
4. With the aforementioned cam, the Cloyes timing set will bolt straight on. The Mopar 29 cam will provide ample low rpm torque without advancing it so you can install it straight up.

Why stock size valves? I've read repeatedly that the exhaust will choke this engine before anything else.

What if I found a mopar 230 cam? Would that be better? I've read that the stock valve train will handle .450' of lift in some places and only .440 elsewhere.

The stock valve springs are rated to 0.440" of lift so the 29 cam is the biggest they'll support.
As for the exhaust valves, there's not much clearance between the valve edge and the chamber wall so going much bigger than stock will cause shrouding problems. LS1 exhaust valves are 1.55" and they're probably as big as you should go if the stock valves need replacing.
The stock intake valves have more clearance so you could go for the 2.00" LS1 valves but unless you really need to replace the stock valves, why go to the expense? Most of the flow gains come from pocket porting the valve bowls/throats and tear-dropping the valve guide bosses. Unless you open up those areas, installing bigger valves won't really help.

I spoke to the machinist about unshrouding the exhaust valves so that was part of the plan. Any reservations with the bigger exhaust valve if this is done?

Digging around on summit today I see that Cometic makes head gaskets as thin as .027". My math tells me this would get me real close to stock quench. It looks like this may bump the SCR by .5. Is this worth looking at? Is cometic worth a darn?

Unfortunately there's just too many compromises built-in to using a stock cast piston combination.

You're just not going to get any kind of an effective quench at .060 piston to head.

There are only really two options. Deepin the existing dish along with cutting about .040 off the deck of the block. I have a CNC program and pistons on the shelf in both 2229 and 667 pistons with volumes up to 26cc
They go for $200.00 a set.

Option two which I think is the more sensible is to buy a custom forged piston from me or anybody else to the exact specification you need utilizing the more desirable 4.0 lengh rod and the hour and a half, and money unnecessarily decking your block .040
Cost of these Pistons are $495.00

When you lose your affective quench you lose your torque. Ideally your piston should be between .035 to .045 from your cylinder head at TDC.

If your able to get over to NAXJA, in the modified section there's a thread that was started by one of my customers that bought one of my 4.6 Stroker kits that included my ported cylinder head and it made 227 HP and 396 TQ to the rear wheels with a mild 68-232-4 Comp and stock exhaust.

My point is with just a few good properly designed engine parts with proper engine specs you can reap some measurable gains without killing your budget

Russ

You're giving me a lot to think about...

Russ, and anyone else who wants to chime in. Is it nuts to swap rods and pistons in the frame? I just pulled a few bearing caps and the bottom end looks great. I have no reservations about continuing to run it as is. Since I'm this deep in to the engine, it doesn't seem like it would be tough to swap the rods and pistons while I'm here. Thoughts?

My only concern is measuring the deck height may be a little touch with the crank in place. Any ideas?

YJLopes wrote:Russ, and anyone else who wants to chime in. Is it nuts to swap rods and pistons in the frame?

With the head off at the top, and the oil pan/pump off at the bottom, it's easy enough to pull out the rod/piston assemblies. Just make sure that you don't mix up the rod caps and rod/piston assemblies as you remove them.
If you have a dial indicator, you can measure the deck clearance of each piston at TDC by rotating the crank.

Cheromaniac wrote:

YJLopes wrote:Russ, and anyone else who wants to chime in. Is it nuts to swap rods and pistons in the frame?

With the head off at the top, and the oil pan/pump off at the bottom, it's easy enough to pull out the rod/piston assemblies. Just make sure that you don't mix up the rod caps and rod/piston assemblies as you remove them.
If you have a dial indicator, you can measure the deck clearance of each piston at TDC by rotating the crank.

That's what I had in mind, thanks for the input.

I did that procedure once upon a time to fix a bent connecting rod. Motor ran strong for 50k miles after that.

If you haven't previously decked the block I'll have a piston combination that'll allow you to drop it in with some predictability of its relationship to the deck height.

We've done piston and rod swaps at the racetrack. Sometimes 5 times in a given day.

Well I lied. I pulled the head and measured the lift directly on the lifters without allowing the plunger to collapse. All lobes appear to be in decent shape. Original lift was .280 on the lobe and the worst one I measured was .272. I wasn't able to take the slop of the lifter out of the equation with the head in place.

With this new information, I no longer had the smoking gun that I thought I had. I decided the only thing left to do at this point was check the cam timing. It is significantly retarded. Everything I've read on overheating (and its been A LOT lately) says that retarded ignition or cam timing can cause overheating. This is somewhere in the neighborhood of 3+ degrees retarded. I'll know more once I pull the cam and verify the grind #.

Russ, I think I'll be in touch this week to talk about pistons/rods. I measured today at TDC I have .040-.044" below the deck to the top of the piston. Will your pistons drop in on a 4.0 rod? I was thinking your setup with a .040ish head gasket would get me where I want to be quench wise, still not sure what to go with for CR and cam.

Somebody timed my '75 Cutlass wrong before I got ahold of it. It was set at 12* instead of 20*. It had no power and ran hot. After fixing that it had...... well, still no power, but considerably more, and it didn't run hot anymore. Not sure if 3* would do that though. 8* could for sure.

I should have a piston that will work for you.
Shoot me a call and we could go over all the parameters