Steel Shims for 4.1L ?

6SENSE

Member
As title says, wondering if there are any steel shim headgaskets available for a production 4.1 ? Bore is 4.20
 

CTX-SLPR

Active Member
Did you bore the block out to 4.020in or is that the gasket bore you are looking for? Cometic gaskets can be had in that configuration but if you're talking about the RJC style steel shims... I don't know of anyone.
 

6SENSE

Member
Quoting my machinist the bore is actually 4 inch 20

I want to make sure that my compression ratio is AT LEAST 8:1 (like stock). I was shooting for 8.5:1 or 9:1 but looks like thats not going to happen.
I got these forged pistons from a board member awhile back and they wound up not being exactly what we thought. Got far enough into it that I was basicaly stuck with them. They have a pretty big dish.
Heres the #s from machinist:

piston & deck = 54cc
head = 42cc
gasket = 8.2cc
cylinder = 707.7
with gasket = 7.8:1
without gasket = 8.4:1

Gasket he used just to get the #s was a felpro that was .039 thick. I think the thinnest cometics are .027 ?
So now you know exactly why I was asking about the steel shims like what came stock on hotair 3.8's. I know steel shim gaskets would only be .015 or .017 and would insure that compression is where I want it.

Thanks in advance if anyone out there has any ideas. I guess I need to do the math to figure out exactly what thickness will get me there, however Im not exactly sure how.
 

83ttypecooled

Active Member
compression

Hi,
Why not shave the heads to regain the compression you lost with the overbore and different pistons? Unless there is some mechanical reason why not to do this, and there is none I can think of,go for it. Pushrod length could be an issue,though.$100 will get you any pushrod you want.Smith bros. is the leading supplier. Good luck with your project!
 

6SENSE

Member
I suppose I could. They are some already done up heads. Really nice, bigger valves etc, that I picked up from Precision Motorsports of Florida/Bob Morreale (bmcomputersource on here). Didnt really want to mess with them.
I'll ask my machinist. I thought I brought up the idea before though. Maybe the issue was just the extra cost? Dont remember.
 

fuzzyGN

Member
I am not sure about the head gaskets but a better way to get more compression is deck the block. Remember, milling the heads gets limited returns (especially the more you go) because the combustion chamber is smaller than the overall bore with the angles and such. Anyway, most blocks could use a little "squaring up" so it becomes a win-win. I milled .025" off the deck of my 4.1 and with the piston I was using was still .055" "in the hole". Still had tons of room to mill more. My 2 cents.
 

6SENSE

Member
Thanks Fuzzy. Only bad part there is that the short block is fully assembled now:( So I guess Im not likely to be doing it.
What final compression ratio did you wind up with on your 4.1?
 

MIB

Member
I think the deck on a production 4.1 is paper thin. I avoided milling the deck to a minimum. What ever gasket you use, make sure your not hanging in the bore. HTH
 

fuzzyGN

Member
I ended up somewhere around 8.4 to 1. My heads were shaved a little too, just enough to make them square. As it turned out the .025 decking was the minimum to make it square too. I was amazed it took that much but whatever works I guess. And yes, don't let the headgaskets hang into the bore unless you like changing headgaskets.
 
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