HO stroker, or non-HO stroker?

I have two high miles XJ's('89 w/240k, 91 w/238k) and I aws wondering which is "better" to put a stroker into?

I searched around for stroker projects, and they all seem to be Renix, is there a reason for this?

Both XJ's are in equaly bad shape, the '91 has a bad rod knock problem,
and the '89 is tired, real tired.

Any sugestions?

You shouldn't be surprised that most of the strokers running around today are Renix versions. After all, the Renix 4.0's are older than the HO 4.0's so they're more likely to have high mileages and be in need of a rebuild.
If you want a suggestion, I'd say build both of them up into strokers.
I have a HO stroker in my XJ based on a '00 block and a '92 head. You can read about my build up by clicking on the link in my pseudo sig. You'll also find more general stroker info. on my performance site.
________________________________________________
Dino's "Mean Green Machine"
1992 XJ Laredo 4-dr - 4.6L I6 HO Stroker - 183k miles - AX15, NP231, D35c, D30

263hp@4900/321lbft@3300-3800, 1/4 mile = [email protected], 0-60 = 5.7secs
Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

One reason the Renix is popular for Stroker rebuilds is the fact it has a knock sensor, needed for the less pricey "Budget Stroker" which uses a combination of factory spec parts. Lots of folks don't want to go through the hassle and expense of having custom pistons made to get the right wrist pin height/compression ratio/quench area combination.

Before rebuilding that 91 because it has a rod knock, make sure you don't have a leak where the exhaust manifold mates to the head or a crack in the manifold. Including myself, I know of several XJ owners that thought they had a rod knock when it was simply an exhaust leak

MistWolf said:

One reason the Renix is popular for Stroker rebuilds is the fact it has a knock sensor, needed for the less pricey "Budget Stroker" which uses a combination of factory spec parts. Lots of folks don't want to go through the hassle and expense of having custom pistons made to get the right wrist pin height/compression ratio/quench area combination.

Before rebuilding that 91 because it has a rod knock, make sure you don't have a leak where the exhaust manifold mates to the head or a crack in the manifold. Including myself, I know of several XJ owners that thought they had a rod knock when it was simply an exhaust leak

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I'm quite sure it is a rod knock, in fact there's a continuous knock/rattle while starting it and at idle, VERY loud at idle, like someone's knocking on a door with a ballpien hammer.
Thanks for the knock sensor tip.

By the way, does a 4.2 head flow better than a 4.0 HO head? I picked up a complete '79 4.2 for the stroker rebuild and was wondering how much I could use.

crazyoffroader said:

By the way, does a 4.2 head flow better than a 4.0 HO head? I picked up a complete '79 4.2 for the stroker rebuild and was wondering how much I could use.

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Worse.

MUCH worse.

Want a real budget stroker? Rebuild the 4.2L, punch it .060 over, and use the 4.0L head and injection. You'll have around 4.3 liters, lots more torque, and most of the compression ratio/quench problems associated with the 4.0L strokers will be done away with because the crank, block and rods will all be correct.

Eagle said:

Want a real budget stroker? Rebuild the 4.2L, punch it .060 over, and use the 4.0L head and injection. You'll have around 4.3 liters...

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Something doesn't sound right with that statement.

4.2 crank and rods + 4.0 block bored .030 over = 4.6L
4.2 crank and rods + 4.2 block bored .060 over = 4.3L?

Using the math for the first engine, the displacement should be > 5.0L, more like 5.1L

What am I missing?

Besides that bit of math, I just might do that. What are the main differences between the two blocks?
Thanks
Nathen

The 4.2 is a small bore/long stroke motor, while the 4.0 is a big bore/short stroke motor. This is why it's cool to use the 258 crank in the 4.0, because you end up with both a big bore and a long stroke.

Will the 4.2 bolt up to the AW4? I don't remember.....but I thought it was different.

If I recall correctly, the 4.0, 258, 304, 360 & the 401 blocks all use the same bell housing bolt pattern.

The 258 (4.2) uses a longer crank throw, but it also uses a shorter rod. This gives you a greater rod angle as the crank turns round and increases piston speeds for the same RPM. More important to us is it decreases dwell time at top dead center. When they made the 4.0, they raised the deck height of the block, shortened the crank throws and increased rod length. This increased dwell time at top dead center, giving the air fuel mixture more time to burn before the piston began it's journey downward on the power stroke. This along with the squish area allowed them to improve torque & mileage over the 258 while cleaning up emissions (fuel injection helped too). An overbored 258 will bring you more power (not sure you can just bolt on a 4.0 head though) but by the same token an over bored 4.0 would be better

crazyoffroader said:

I'm quite sure it is a rod knock, in fact there's a continuous knock/rattle while starting it and at idle, VERY loud at idle, like someone's knocking on a door with a ballpien hammer.
Thanks for the knock sensor tip.

By the way, does a 4.2 head flow better than a 4.0 HO head? I picked up a complete '79 4.2 for the stroker rebuild and was wondering how much I could use.

Click to expand...

That describes what you'll get with an exhaust leak. Mine was so bad I bought a new rig to drive until I could get the engine in the XJ overhauled. (I felt pretty foolish to discover it was simply loose manifold bolts!) Most exhaust leaks grow quieter when you accelerate & the RPMS go up. The 4.0 rarely develops a rod knock unless badly abused. Before comitting yourself to to an expensive engine rebuild, inspect your exhaust manifold for cracks, loose bolts & a bad gasket. Nearly all the factory manifolds crack at the Y

That also describes a cracked flex plate - which is how my buddy the used car dealer bought several XJ's with "bad motors" for peanuts and sold them as good running XJ's after replacing the flex plate.!!!!

rsalemi said:

That also describes a cracked flex plate - which is how my buddy the used car dealer bought several XJ's with "bad motors" for peanuts and sold them as good running XJ's after replacing the flex plate.!!!!

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Agreed, I parked my XJ about five years ago (with 100K miles), and bought a car to drive while waiting on a rebuild after several mechanics diagnosed it with crank failure. Turned out to be loose flexplate bolts. After another 100k I think it actually does have some rod noise now.

One more question? Will the HO head fit on a Renix block? I didnt know if they changed anything. I have a 89 xj and was wanting to build the lower end & switch the head & int. I did the hole HO swap in one of my xj's a few years ago & wouldnt mind doing it again with out buying a block.