1st off, I really don't want to go overboard with building a stroker unless I can find some off the shelf pistons to use AND run 87 octane. I've done some reading and it doesn't seem like there are any that are worthwhile. Maybe I'm wrong. Yes, I know Russ Pottenger makes stroker pistons. They're also over $500 for the set. For JUST the pistons.

That being said, I've looked into swapping a 4.0 HO head on an old 258 block for slightly more displacement. I see it as a "middle of the road" build between a stroker and a stock 4.0.

What I'm seeing, though, is that most people just slap a 4.0 head on a 258 and call it good. They claim about a 40hp increase. I guess that makes sense if they're using the original 258 cam.

But what if attention to things like quench, compression ratio, cam specs, etc were considered?

What I (think I) want to do:
258 block, crank, rods, pistons (probably a slight overbore)
4.0 cam (maybe a mild comp) , head, Victor Reinz .028 MLS head gasket
Block decked .090"

The following pictures show what I've calculated.

1st is the 258 completely stock, which I think might be wrong. I don't know what the actual deck clearance is, but I *think it's 0.110". So I'm going off that for now.

2nd is the 258 without having the block decked and a 4.0 head. Static CR of 8.34:1, but a miserable quench of .139. Yikes.

3rd would be the 258, decked .090". Static CR of 9.88:1 and a tight .048" quench. Seems like a high CR, but with that quench I don't think detonation would be an issue.

Sounds like a lot of work, but it's pretty much a normal rebuild with some machine shop work and some slight modification to the 258 for that coolant passage blockoff.

 

My 92/96 stroker and my 01/98 stroker all used the 4.0 block and the associated 4.0 head with the 258 crank. I had the 258 rods and 4.0 pistons. To keep the compression manageable i had my machine shop take the standard 4.0 D dish pistons and open the same depth D to a full circle to drop the compression. I ran the comp cam rated for the fuel injection models and my strokers measured about 4.7 to 4.8 disp. I didn't grind the block or head and used a felpro HD head gasket which is on the thicker side. I upgraded the injectors on both models approx 20% from stock flow on both...have been running 87 octane in both for well over 100k The 92/96 is dead now 5 or 6 years but only "pinged in high gear / overdrive on big uphills, running 31's on stock rear...The 01 does not ping ever unless im really giving it gas below 1500 rpm on a monster hill...same 31's. Stock gearing . If i drop into 3 on those hills to keep rpm over 1500....purrs like a kitten..no pinging. Its been 3 or 4 years since the build and i don't have all the spec numbers any more but I have done a compression test over the summer and the 01/98 runs 165 -180 psi on the compression gauge..i think my pistons might have been .020 or .030 over. Let me know if i can answer any of your questions

 

Ever searched "poor man's stroker"?

 

https://www.jeepstrokers.com/forum/

 

Yeah, I'm well aware of it. While there is a plethora of information out there on stroker builds, there is also a lot of bad information. The "poor man's stroker" uses the 258 rods and a 677cp (no longer available, so must use the 677ap) pistons. The result is a stroker with a quench of 0.088" and it's (supposedly) quite susceptible to detonation. I need to run the numbers to see what the static CR would be if I did that AND milled the block down to get a better quench volume.

Also well aware of that page.

bluejeep2001- I did consider milling down pistons like you mention, but I really didn't want to have to result to a full circle dish. The full circle dish ruins any squish effects from the quench volume discussed earlier. D-shaped pistons allow for compression relief with the added benefit of the quench area. Ideally, the d-shape would be offset from that of the cylinder head.

My original question, condensed, still stands. Is it worth it to go through the effort of using the 4.2 bottom end and 4.0 HO head, or is the juice not worth the squeeze and I should just stick with a stock 4.0 rebuild? I'm really hoping a longer stroke would aid in low end torque, and the 4.0 head would wake it up at the top end.