Head gasket choice for compression

[Aproductions]

So during my build I ran into an issue.

Basically, for the headgasket I could run a regular Cometic MLS but I am wanting to keep the compression down. I guess I ordered the wrong pistons and when I got the block and head decked it changed my compression from 9:1 pistons to 9.6:1 if I use a .053 headgasket.

I wanna know if it is safe to use a .070 thick MLS headgasket instead. it would make my compression 8.8:1 and that is better.

Keep in mind this is a MLS gasket and not a composite.

Also the pistons do not protrude the block at all, I am simply just wanting to lower my compression.


Thanks.

 

[BigBeans]

Alex, you are WAY over-thinking this.

You already made a thread about this. The car will be fine with a slightly thicker than stock gasket.

Like i told you in the first thread, i've had no issues with 30+psi on a cometic .066.

If you want further proof, i just stretched a set of ARP studs and the gasket was completely fine. Clearly it's not a weak component.

Also, HKS, Power Enterprise, Cometic, and other performance brands all make MLS gaskets that are .065 and thicker. I don't mean to be rude, but do you think all those companies would be making these thicker gaskets, for performance applications, if they fail?

If you're that worried about it throw a cooler t-stat in the car, adjust your coolant offset accordingly (I assume you have DSMlink?) and the lower temps will reduce load on the HG.

 

[VETDRMS]

I am using a .066" Cometic for my 2.4 build with a static compression ratio of 9.6:1. On a wedge-type head (Chevy) quench is more important (I run .035" piston to head clearance in my 7500rpm 406ci SBC). It really isn't as big of a deal on these motors.

 

[Strm Trpr]

How much was removed from the deck surface of the block, and was the block stock?
Do they happen to know what the new Deck Height is?

How much was removed from the deck surface of the head and was the head stock?

Finally what brand and part number pistons do you intend to run?

 

[99gst_racer]

They make MLS gaskets all the way up to .120" thick. You'll be fine with a .070 thick gasket.

 

[Aproductions]

Alright, thanks guys, I'm sorry. Someone fed me some info on quench and it scared me, I wanna do this 1 time and the right way.

Storm trooper, my pistons are the Manley 9:1 platinum and the rods are the Manley h beams.

I don't know how much the machinist took off of the head and block but I know I need a .075 for a 8.6:1 compression.

I wanna do a .070 thick one though because 8.8:1 is a good compression and I was scared of the .075 one.

But yeah I am only doing this to lower the compression, but since there will be a bigger gap between the piston and head, wouldn't that cause any problems with AFR and stuff?

Or maybe I am confused on what quench is, this is an article from Dsport Mag.

 

[BigBeans]

AFR? As in air fuel ratio?

 

[Aproductions]

Idk read the article I posted, it says mixing contributes or something.

What exactly is quench? Is that article saying not to use a thicker headgasket because the distance would be bigger from the head to the piston?

 

[BigBeans]

Quench is for wedge style heads, not 4 V heads, and has nothing to do with AFR.

Put that book down, it's for 1950's chevy's.

 

[Aproductions]

No. DSPORT MAG is a import performance magazine and right after the article, it talks about a RB26DETT.

This is the same magazine the STM's ricer evo is featured in. (DEC 2010)

 

[BigBeans]

No. DSPORT MAG is a import performance magazine and right after the article, it talks about a RB26DETT.

This is the same magazine the STM's ricer evo is featured in. (DEC 2010)

I don't know anything about RB26s, but our engines are not quench engines.

"Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench. "

There's no significant flat area on the deck of the head, and most pistons are dished, therefore no quench.

The area between the top of the piston and the flat part of the head, on the left side of the combustion chamber is quench area. We don't have it.

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Here's a detailed article on it.

http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/index.html

 

[Aproductions]

Okay well thanks man, I was really confused.

Now the question is...

8.8:1 (.070) or 8.6:1 (.075) compression?

 

[BigBeans]

Okay well thanks man, I was really confused.

Now the question is...

8.8:1 (.070) or 8.6:1 (.075) compression?

No problem, bud.

Now that's up to you, but it won't be a significant difference either way. I believe you said in the other thread that you were planning to go with meth most of the time, so personally i'd go with the slightly higher compression for your setup.

Good luck with whatever you choose, but you can't go wrong with either.