Dave69Z

My JE Custom pistons are on the way....ordered them for a 57cc Head while waiting for head porter to finish heads. When my heads were finished, they cc'd at 62cc, much higher than expected.

This drops my compression about a half point lower than I expected, I am considering my options...don't want to angle mill my AFR Heads as the engine builder explained that could necessitate a new valve job.

Figure my only other option is to swap to a thinner head gasket, I have Felpros right now. Besides the Impala Head Gasket, does anyone else make a .029 or so head gasket for LT1s, that could stand a 200-300 shot on a 396 (actually 392 or so.... .010 over).
Does ROL or Victor Reinz? Anybody have any experience with either of them?

Thanks, Dave.

Soma07

Mr. Gasket makes a .026 gasket and its the thinnest I've heard of. However their catalog claims its for iron heads only. They list a .046" gasket for alum heads but thats almost as thick as stock.

Here is a link if you want to take a look yourself.

TAYLORMADE

Milling heads won't effect the valve job unless it gets into the intake seat which is highly unlikely, unless the heads have been severly angle milled or had excessive amounts milled of them. I question you're head guy? You may have to remove the intake valves to mill the heads if the valve protrudes the head surface but other than that mill away.

Dave69Z

I think I will just get the heads from the head porter and take them to my machine shop and see if they can be milled without getting in to the seat

They heads are not assembled at this point. So don't have to worry about removing the valves.

I really need to think hard about whether approximately a half point of compression is worth the extra work. Going from approximately 11.4 to closer to 12.1

Thanks for the information.

Dave.

arnie

It is obvious to me, from reading on this forum, that 98% of the posters here, pick and choose their gasket thickness for the wrong reason. The choice of gasket thickness is/should be done primarily and foremost for finalizing deck/quench height. PERIOD! Compression ratio consideration need not apply. That is what the comb. chamber cc volunme is for.

Fast3rdGen

i have an old school type sbc and felpro makes a .015" gasket which i am using....ya might look and see if they make it for lt1's as well.

OneFlyn95z28

we know how you feel Arnie


I am using a Imp Iron head gasket..026 crushed. Fel pro makes a .039. seeing how I have a stock motor the .026 will give me a .050 Quench. best I can get till I build a motor so i take it

Good luck!

SStrokerAce

Right on!

On top of that if you are running a zero deck engine than a .026 gasket is going to get you into some dangerious problems at high rpm.

I'm suprised nobody has mentioned rod stretch. All rods stretch and with a quench area that small and these long of rods you'll get the piston actually hitting the cylinder head, that's a sure fire way to break $hit.

If you want to change compression ratio, change all the other factors first leave the gasket thickness in the .030-.050 range PLEASE, in fact to be safe .040 is about perfect and shows about the same power as a smaller quench area. (this is all based on a zero deck height block, I'm sorry I don't fool around with non zero stuff much)

I would mill the heads, just don't get into the seats and make sure that your piston valve reliefs are o.k. for that reduction in free drop.

Bret

George Debski

Hey Dave,

On my Impala, with 420HP NA, I'm shooting an additional 200 on the squeeze. Of course, I'm running the stock Impala gasket with my ported iron heads and stock GM head bolts and haven't had a problem so far (3 years).

My quench height is 0.051"

JordonMusser

as stated, DO NOT adjust head gasket thickness for compression reasons! deck height and gasket should be setup for .035-.045 quench, and the compression should be set with piston dish/dome and chamber volume.

Sounds like your porter is full of ****. unless the heads have already been milled a TON, you don't need a new valve job to mill them. I would flat mill them also, unless it needs angle milling.

with that said, I would just stick with 11.4:1. imo that last .5:1 isn't gonna do much for power, but could put you over the edge detonation wise. ie, 11.4:1 is not pushing it, 12.1:1 is.

SStrokerAce

dudes right.

With street gas detonation is really hairy in a Gen I or II SBC over 11.5:1, 11.75:1 to 12:1 is hairy I know. I would just make sure that the quench area is right (.035-.040) and call it a day. It's a much better combo.

Bret

Dave69Z

Thanks for all the information. I am realizing the my ignorance, and that is why the engine builder is making all the decisions concerning the engine assembly and not me.

I am sticking with the Felpro Gasket and I am not going to try and have them raise the compression. I agree it is not worth the expense or the hassle it could cause while running on pump gas. Better safe than sorry.

I am pretty confident in my engine builder, and I think they already covering most of the concerns you have covered (I was one curious about head gasket...asked question with just doing the right thing and just asking the engine builder...I just feel like I am hassling him calling and asking additional questions, etc.). I am sure they have already decided on the proper quench to shoot for...I have simply never asked.

I do know my pistons are going to be .010 in the hole because of the rpm involved and the fact that I will be squeezing it sooner or later.

Again thanks for all the input and for enlightening me more on this issue. I never realized the importance of a head gasket in setting quench, etc....always just looked at it as being used to seal the heads to the block. Not no more.

Dave.