350 Head Gasket

[Dave Gantz]

I have Goodwrench 350 in my truck. I'm putting head gaskets on it. (I actually pulled the motor to re-gasket and re-seal the whole thing.)
The thing probably has 8.0 to 1 compression, I'm guessing? I don't want to give up any. The gaskets that came off it are about .017". I have a pair of GM #10105117's, that are supposed to compress to .028" (they're .034" now) . Then there's the Felpros's that are about .039", compressed. I see these: http://www.summitracing.com/parts/FEL-1094/ are .015", but are for a 4.100" bore. What's my best option? I'd like to keep as much compression as possible, without doing anything besides the gasket. Is there a direct replacement for what I removed?

[Alan Roehrich]

Yes. FelPro has a steel shim, as does Mr. Gasket. They used to both be in the 0.016"-0.019" range.

[G Anderson]

GM also sells steel shims(don't remember the No.)they have possibly a Teflon or something like that,sealing compound sprayed to the outside and measure around .022 uncompressed

[Greg Hill]

I might be more inclined to have the heads cut a little and use a good composition gasket instead of steel shim ones.

[Dave Gantz]

The only "thin" ones I've found are for a 4.100" bore, it's standard at 4.00". I'm wondering how much I'd lose if I used the bigger bore gasket.
I'm leaning towards the .028" GM. I'd like to avoid machining, as to get it up and running. Also, as Greg mentioned, a steel shim might not be the best bet.

[Alan Roehrich]

Dave, only Cometic makes bore size specific embossed steel shim gaskets. Most of the off the shelf stuff for a 4" bore is actually 4.080" to 4.1" bore.

And yes, ideally, take 0.030" off the heads, and use a FelPro blue gasket.

[BillK]

Dave,
A couple of guys have recommended milling the heads. You did not specify the year of the Goodwrench engine but most of the late model heads are pretty thin on the deck and milling them more than a clean up cut is asking for trouble in my opinion. On some of them, milling them .030 can actually lead to the gasket not sealing in at the "scalloped" shaped cooling holes.

Its ok in a race engine where you are trying to get every bit of possible power and longevity is not a real concern. I think you want to put this thing back together and drive it another 100K miles ...... if so I would just use the Fel Pro stock replacement composition gasket and don't worry about what little compression you might lose.

Just my opinion,

[Dave Gantz]

Thanks for the information, guys. I should've mentioned that the .028" gasket is a composite. I'm going to go with that one.
Before I took it apart, I was "assuming" it would have a .039", or so gasket, thinking that what Chevy used is about the same as aftermarket. I ordered the .028" figuring I would at least pick up a little, maybe a half a point. Turns out I'll lose a little.
The engine is out of a 8500# step van, used for work. It got 8 mpg when I bought the truck 4 years ago. (The truck is a '75. The engine is a Mexican 2 piece rear main seal crate.) I put 1 1/2 diameter headers, dual exhaust and played with the distributor curve. Now it gets 8-9 mpg. I just figure that at 8500#, it's not going to get much better. But, being a tinkerer, while I have it apart to stop leaks, I am trying: Advancing the cam 6*, using 1.6 rockers, and I was going to try bumping the compression a little. It's not worth machine shop time to me though. For one, I wouldn't know where to get machine work done where I live now, and mostly, I need the truck!

[Rsmith38]

On my 78 C20 I started at 8 MPG but was able to get it up to 13+ (on highway) Advance weights were frozen, used light springs; but the greatest improvement was the adj vac advance. I beleive I ended up at 41 degrees - just kept increasing it until it pinged.

[Alan Roehrich]

I would not advance the cam 6 degrees.

Were I you, I'd consider a mild camshaft and a really good timing set instead, with a new set of valve springs and seals. I've had really good luck with some of the budget cams that Speed Pro sells, as well as one of the small Melling cams. I buy them in kits, with lifters, they are pretty inexpensive. I usually put something simillar to the old stock Z-28 spring on them, they're inexpensive, too. A really good timing set will prevent the near instant slack you get with the cheap ones, and the stock ones, because the sprockets are not heat treated. You can often do the whole job for under $250, and you probably have it apart far enough to do it all easily.

A real good tune, as suggested above, will do a lot.