Stock compression height: 1.601"

Sealed Power H802CP : 1.592"

Sealed Power H825CP : 1.592"

Silvolite 3241HC: 1.592"

Silvolite 3242HC : 1.592"

Any idea why every stock 4.0 rebuild piston listed (that I've found so far) has a compression height that's 0.009" shorter? Does anyone sell off the shelf pistons that's actually correct?

 

The only reason I can think of is they may assume that people have machined head or block, so allowing for that couldnt hurt

I hope that reason is not too lame for ya

 

Considering the stock quench height is 0.073" (which already sucks) it still doesn't make much sense at all. I'd have to mill the deck quite a bit to not end up with an .082" quench height on a stock rebuild.

I just find it hard to believe that everyone rebuilding their 4.0 is ok with running pistons with shortened compression heights and terrible quench areas.

I do, however, see that there's a Victor Reinz 61-10375-00 available that is .028" thick MLS. This would raise the static CR to almost 9:1 with a quench height of .058".

The only problem is that I've only seen one website offer specs on that VR head gasket, and that's Rock Auto.

 

Another wrinkle: Ring size. There was a write-up in Hot Rod a couple months ago about how thinner rings not only reduce friction (heat) but also last longer, less wear on cylinder walls, and produce more power. It was kind of a fascinating read. If you're contemplating replacing the pistons, that (also) might be another consideration ...if yer rebuilding your XJ's engine. (thinner than stock rings).

https://www.motortrend.com/how-to/pi...HRN:trueanthem

 

Last 4.0L I rebuilt, I went with Mahle pistons. Pretty sure they retain stock compression height.

MAH-2243415

Also, keep in mind, 96+ use the smaller metric rings. All the older ones use the standard larger rings. Either set can be used.

 

I thought you may have been onto something there 5speed. I really haven't seen Mahle pistons when looking for replacements. Most sites don't have them in stock any more. Even more interesting is that Mahle (from the castings of the old pistons I pulled) IS the OE brand. But check this out:

 

Well thats a bust. You would think since they are the oem manufacture, their replacement parts would be oem specs. Looking back at some of my notes, I used this part number piston set on a different build. Betting they are .592 as well....

CPW3758

Edit - sadly I can't find my notes on how much the block was shaved or how far in the hole the piston sat. I will have to say, if it was out of spec, I wouldn't have run it.

 

That PN shows it's for a 5.0 Chevrolet V8? I did some searching and only found your thread where you said you used that part number piston set, and this listing for some ebay pistons.

However, I did find that CPW listing for some 96+ 4.0 pistons. They don't list any specs at all though.

Honestly, if I don't find the correct ones, I'll probably end up decking the block and using the Sealed Power pistons. It just sucks that it adds the cost of having to deck the block to get the right specs for everything.

 

Yep, that looks like kit I got from Car Parts Wiz. Probably wrote down the wrong part number in my post. Pretty sure the pistons were made by Enginetech. Honestly, all the pistons probably come from the same manufacture.