Stock 4.0 Rebuild with questions

[92-JEEP-CHEROKEE]

Hey guys! new guy here... I have some exp building small block and big block Chevy, not the 4.0 though. I am looking for a very mild rebuild. would like to bump the compression and find some type of RV cam that will work with oem replacement springs.
on my 92 4.0 (not stroking) I want to use pistons from a 96 and up motor. is this ok? I was told it would be. I was told it would raise the compression.
I am good with the higher compression, I live @ 5000 ft now and will be driving it to higher altitudes. also what compression will that get me 9.5?
any cam suggestions?
thanks

Aaron

[lafrad]

My project thread is here:
http://www.jeepstrokers.com/forum/viewt ... ?f=8&t=776

Some of the "head" changes are here:
http://www.jeepstrokers.com/forum/viewt ... f=5&t=1433


its basically:
'99 block, bored 0.030,
4 CW 4.2" crank with a mild offset grind (to achieve 0 deck on the pistons).
Sealed Power Hypereutectics, dished to 20cc's.
rods are aftermarket repops of the 4.2 rods.

CR measured out to be 10:1

Cam is a Crower cam, the "CompuPro level 2"
http://crower.com/misc/m_cat.shtml

I set the cam up at 0* of advance... idles real smooth and has a ton of torque and HP. no ping on 91, haven't tried 87 yet.... and I'm not too far from sea level.

[4.whoa]

I haven't heard of different year pistons having more comp. before- you'd just have to check dish vol's. You can always "zero" deck the block and shave the head to get comp up-that's what I did. had 0.040 milled off head and 0.035 off the deck...............well thats what he was supposed to do.I didn't have any way of measuring myself. I'm not real sure where it ended up (if i knew then what i know now.. ) but it runs REAL good. 4.0, 0.060 over , 68-231-4 cam 4*adv.

wheels up.jpg

best 60' so far was low 1.90's gotta love that torque! at least untill you find that "weak link"

[Don H Jr]

RUSS: What you did get is the quieter coated hyper pistons instead of the uncoated, loud slappers like I have in my stock 1994 pistons.

You got the improved versions...stock from the factory. It constantly amazes me how the factory did not have this long running I6 sorted out, right to the end they were sabotaging their own engines, with stuff in the 2000 era of over catting and cracking heads. Crazy all the tiny bad engineering flaws in a basic classicly strong engine. In my year 1994 I have different/assorted sized pistons in the same engine and possibly bearings the same way with letters painted on side of engine block telling which cylinder has which sized pistons and they still slap like crazy and needed coating like your skirts got.
Go figure and with all that going on, at 266,000 still runs without burning oil.
Don Jr

[SilverXJ]

RUSS: What you did get is the quieter coated hyper pistons instead of the uncoated, loud slappers like I have in my stock 1994 pistons.

The coating has nothing to due with noise reduction. Its purpose is to prevent wear of the piston and cylinder walls. The coating just wears off any how.

[Don H Jr]

O. I C.

Jr

[Don H Jr]

Silver: does it wear off the Hesco/Diamond piston skirts and tops too?

Jr

[SilverXJ]

I don't know what Hesco uses on their pistons. I doubt the coating on the top wears off though. The skirts, possibly. The usual material for the coating on the sides is moly. The top coating has a different purpose from the skirt coating and different properties. The skirt coating is to reduce friction while the top coating it to reflect heat back into the combustion chamber.

I would recommend coating the top of the piston.

Both the skirt and top coating need to be taken into account when figuring clearances.

[Don H Jr]

Silver: If the coating on the skirting just wears off like you said in your first post, then Hesco and Chrysler must have just put it on for break in purposes...is that what you are saying?

Don Jr

[4.whoa]

Don I don't have any coatings on my pistons.the short block was from advance auto. nothing exotic, not OEM, bigger dish than stock pistons had. I wasn't talking about pistons anyway, just about picking up my compression, and that it worked for me. The moly coatings that some pistons have wear, but not "right off" they are a friction reducer,which helps with longevity and wear reduction. they last WAY longer than just break in.I think Silver was just sayin they do wear.I've heard that there are do it yourself kits and that you can even send old pistons to be coated to compensate for mild wear,haven't done it myself. However, i've also heard that THOSE types don't last anywhere near as long as ones from the pistons mfg.

[Don H Jr]

Whoa: Thanks for trying to answer this one but was between Silver and myself mostly. I just wanted to see what the rest of his answer was, it doesn't mean I went along with anything he said on the subject, I just wanted to see where he was going to take it from there. I figure Hesco and Chrysler Corporation both know more than we do on this site about coating pistons.
Don Jr

[Don H Jr]

Russ: What is that shiny thingy sticking up through yur hood?

Don Jr

[SilverXJ]

Silver: If the coating on the skirting just wears off like you said in your first post, then Hesco and Chrysler must have just put it on for break in purposes...is that what you are saying?

Don Jr

Maybe its there for break in , maybe not. It is there to reduce friction and prevents scuffing. So possibly will help in the first minute a virgin engine is run. Its just more crap for the oil pump and filter to deal with one it rubs off. I have a set of pistons with about 5000 miles on them and while the coating isn't completely worn off it shows a lot of wear or something with only 5000 miles on it.

As for Chrysler... your talking of the same Chrysler that used the flawed 0331 head, is currently trying to sell a $8000 stroker, managed to make a mess of teh 4.0L by the end of its run and, killed off the Cherokee? Enough said. with that

And Hesco. They are trying t make money. Coatings will bring in extra money, so why not offer them. I would like some of that heat reflective coating on the valves, combustion chamber and piston top.

[lafrad]

Coatings are great!

Even if they wear off the high points of the piston, they are still in the depressions, and they STILL take the brunt of the force of all the scuffing when the piston is cold and un-lubricated...

I've had quite a few engines apart, and no matter WHAT the miles, the engines with coatings ALWAYS came apart with SIGNIFICANTLY less piston and bore wear than engines WITHOUT coatings.

[4.whoa]

That is a "hilborn" style scoop (supposed to be on a carb). I didn't care much for the CAI's (or their prices) that I was finding online, so I adapted this one. Completely fresh air and you wouldn't believe the attention it gets at the track Its weird, it was pulling wheelies with a stock looking hood and no-one gave it a 2nd glance, but now guys stop unloading their rails to watch me tow it through the pits go figure