On a .040 over 350, with 6cc valve relief flat-top pistons, 6" rods, and an XE284 (284-296 adv, 110LSA, 106 ICL), and 76cc heads.

I found a copper head gasket with 4.060 bore and .030 compressed thickness. My pistons are .003 down. Using Pat's calculator, this is 9.2 CR and 8.1 DCR. I like the numbers, as long as .033 quech distance isn't too small. Any opinions? Thanks! smile.gif

Chris

.033 will be fine. In an unintended experiment, I discovered that .021" is too close. The pistons hit and were smashed about .002-.003". Judging from this, at least in my engine, .026" is the tightest I would go. This in a 355, forged pistons (.004" clearance), 6" rods, .002" rod bearing clearance. The engine goes to 7000 rpm.

Thanks for the quick response! I thought I had read that .025-.028 was a good minumum, but I'm glad to hear that .033 is good. Do you think that the DCR and combination is ok? I've never used a copper head gasket either...

chris

Before I would use the .030" copper headgasket, I would stack two, .015" thick, Fel-pro #1094's!!

Just gaum them up good with Copper-Cote on both sides and stack away!!


OR cheaper yet, use two .020" thick standard steel Mr. Gasket shims!! They are like $16 to $18 /pair ordered plus S&H vs $19+/single next day over the counter for the 1094! That way, you will still end up with a .043" quench which to me is FINE!!!! (.035" to .045" quench range to me...)

I just checked at Autozone this afternoon for my 283 motor....

pdq67

PDQ, are you sure the rubber coated gasket can be stacked. I know plain ones can. My understanding, and I've never used them, is the rubber coated gaskets should go on without any sealers.

Chris, GM has a .028" gasket that should work. gives you .031. Victor has a .026", that I'm using, gives you .029". Fel-Pro has a .018" shim (less than $7 each), I use this in my driver. Stack 2 for .039" quench. You actually have a number of options.

from the cam and stuff you mentioned, this appears to be a street engine. You should be aware that copper gaskets have a bad reputation for seeping/leaking water over time. Not a problem in a race car that's torn down all the time, but not good for a long-life street engine.

Tom

Pat,

I wouldn't see why not..

I would just gaum them all up real good and let them all get almost dry, but still tacky and install them and then do about three more torque checks over two day's, (hot, then cold sorta deal, etc..), or so just like I do my other headgaskets b/c I'm almost anal over headgaskets!!

BTW, Pat, what's the part number on the .018" thick Fel-pro shim?? I'm chea--, er, eh, "frugal", so may use them instead of the $19+ each 1094's on my 283...

pdq67

IMO,
.033" is too tight.
When you figure the thermal growth of the piston and rod, then the bearing clearance, potential crankshaft stretch, thermal growth, etc. this is getting close.
I was having this discussion elsewhere some time ago and someone posted the growth rate of 4340 per inch... Might wanna go find it yourself.

I shoot for a .038" minimum.
A couple of thousandths tighter on a 4" bore motor may be OK but is questionable IMO.

On a street motor you also have to account for cylinder wear, and then piston rocking, as well as carbon buildup.
Doesn't take long for a couple or three thou carbon on the piston and head to eat away at that cleearance.

In a motor that would never see the wear a street motor or long living bracket motor, then .033' MIGHT be ok.
I've heard of contact marks on a 355 with .034" quench. Contact marks in the carbon...

With .003" deck clearance, I would run a .039 composition gasket and be done with it. That would put you at .042 which is in the IDEAL range for quench.

PDQ, I'll have to get the number for you on Monday. Best to remind me.

Thanks for the tips guys.... I 'm gonna look for another gasket. It is a street engine, and I don't want the copper head gasket to leak over time.

Where is a good place to find gasket specs? I didn't see the GM or Victor gaskets in my searches. All I cold find was fel-pro and milodon. Thanks again!

chris

As stated before, I would run a typical Fel-Pro .039 gasket. FP-1010 will work.
Or a Mr. Gasket .038 thick PN 5800.

Pat,

He, He!!

It's Monday..

Thanks,

pdq67

I forgot and it's too late now. Tomorrow.

Gotcha, I'm kinda thinking about bed myself...

pdq67

Part number for the FelPro .018" shim is 7733SH-1. My local machine shop sells them for $6.63. IIRC, Autozone wanted about $11.

Thanks Pat!

I'm gonna save this..

pdq67

Glad to help smile.gif