Head gaskets in the combustion chamber

vette427sbc

Well-known member
Joined
Sep 25, 2008
Messages
1,034
Location
Jersey Shore
Im having a seriously difficult time finishing the engine build for my fathers '55 chevy...
Background:
Bought a Dart SHP block, forged internals, flat tops, etc... 4.155 bore. The heads are standard off the shelf AFR 195's with the 75cc chamber. The drawback of the shortblock that we have is that the pistons are .025 in the hole (got a good deal on it). With the 75cc head, we are trying to get a reasonable compression ratio and quench with a thin gasket.

First gasket set- ECS steel shim. .015 compressed. Perfect for quench and compression. Problem- hung into the combustion chamber too much.

Second gasket set- Custom Cometic. 4.185 bore .027 compressed. STILL hangs into the combustion chamber near the valves.

THIRD gasket set- Custom Cometics again. 4.200 bore, .020 compressed with a bump out for the valves. I can still catch my fingernail on the gasket near the valves.

What gaskets are people using on these AFR heads??? Or do they not check the gasket fit before using them? The recommended Fel Pro gasket is way to thick to use in this application. I assume it is not OK to have the gasket hang into the combustion chamber?

If we can ever get the correct head gaskets for it, it should be a sweet little stroker... 406 cubes, AFR heads, billet core comp solid roller. Cant wait to roast some tires with this one :bounce:
 
The pistons are dished ?? with 12cc dish, .025" in the hole, .040" compressed gasket you somewhere around 9.2:1 CR ... not much at all....

Even with a .025" thick gasket it's not great, hopefully the pistons are 5cc dish or flat top....

If it was me, I'd have the heads surfaced and use a .025" or thicker gasket.

Now, if the gaskets you've got are slightly bigger than the bore then you're good to go... think about it: if the 4.200" hole in the gasket is not big enough then the 4.155" hole in the block isn't big enough either....
 
Flat tops... with the .020 gasket I think we came up with 10:1...
The recommended fel pro gasket has pretty pronounced valve cutouts. The tech at AFR said definite no go having the gasket hang in the chamber. It would create a hotspot and burn up the gasket. The cut outs in the Cometic gaskets are there, but just not enough.
 
Something is funny. A 4.155 bore and a 4.185 gasket is hanging into the bore? should be .030 back from the edge by my math. The head shouldn't care- it's flat
 
Im having a seriously difficult time finishing the engine build for my fathers '55 chevy...
Background:
Bought a Dart SHP block, forged internals, flat tops, etc... 4.155 bore. The heads are standard off the shelf AFR 195's with the 75cc chamber. The drawback of the shortblock that we have is that the pistons are .025 in the hole (got a good deal on it). With the 75cc head, we are trying to get a reasonable compression ratio and quench with a thin gasket.

First gasket set- ECS steel shim. .015 compressed. Perfect for quench and compression. Problem- hung into the combustion chamber too much.

Second gasket set- Custom Cometic. 4.185 bore .027 compressed. STILL hangs into the combustion chamber near the valves.

THIRD gasket set- Custom Cometics again. 4.200 bore, .020 compressed with a bump out for the valves. I can still catch my fingernail on the gasket near the valves.

What gaskets are people using on these AFR heads??? Or do they not check the gasket fit before using them? The recommended Fel Pro gasket is way to thick to use in this application. I assume it is not OK to have the gasket hang into the combustion chamber?

If we can ever get the correct head gaskets for it, it should be a sweet little stroker... 406 cubes, AFR heads, billet core comp solid roller. Cant wait to roast some tires with this one :bounce:


You should be using the Felpro gasket reccomned by AFR the felpro performance gasket are notched for the intake valve deshrouding done by AFR. There is a reason the want you to use the proper head gaskets!!!

[ The drawback of the shortblock that we have is that the pistons are .025 in the hole (got a good deal on it). /B]

Does not sould like a great deal now LOL. and running the recommned gaskets and having .065 quench is not the hot set up either as it will be prone to detonation.


Good luck
 
You should be using the Felpro gasket reccomned by AFR the felpro performance gasket are notched for the intake valve deshrouding done by AFR. There is a reason the want you to use the proper head gaskets!!!

[ The drawback of the shortblock that we have is that the pistons are .025 in the hole (got a good deal on it). /B]

Does not sould like a great deal now LOL. and running the recommned gaskets and having .065 quench is not the hot set up either as it will be prone to detonation.


Good luck


well.... he's got a Dart block, forged internals and AFR heads... after all that money spent it's probably best to bite the bullet, pull the rotating assembly and have the block decked. That way you can use the recommended ("correct") gasket and have good quench.
Shaving the head and using a thinner gasket is likely going to work but then again, after all that money spent I would hate having to be second guessing my engine build....
 
Boost the snot out of it and forget about the whole quench, not an issue on boosted engines :D there...fixed :D
 
You should be using the Felpro gasket reccomned by AFR the felpro performance gasket are notched for the intake valve deshrouding done by AFR. There is a reason the want you to use the proper head gaskets!!!

The drawback of the shortblock that we have is that the pistons are .025 in the hole (got a good deal on it).

Does not sould like a great deal now LOL. and running the recommned gaskets and having .065 quench is not the hot set up either as it will be prone to detonation.


Good luck

Who would have thought it would be this difficult to get a thin gasket for such popular heads?? We'll still be ahead with this shortblock purchase if all goes well... Cometic is taking back these gaskets. They said they sent the wrong ones. The 4th set (and hopefully last) of gaskets will be here Friday. .45 quench isnt terrible... Not what we would have wanted if we had the choice though.


Boost the snot out of it and forget about the whole quench, not an issue on boosted engines :D there...fixed :D

Thats what I suggested! I had a lead on a D1SC too... My father seems to think there is such a thing as too much power :skeptic:
 
Top