6togo

iTrader: (13)

On a LSX block with 4.125" bore what size gaskets do you use for the bore? I think i seen 4.130 and 4.150" Then even higher!

87silverbullet

iTrader: (11)

The rule of thumb has been .030 bigger than your bore.

I have used bigger and thicker to drop compression to go FI on a N/A application.

cmac06

iTrader: (16)

LS7 uses a 4.150 gasket at 4.125 bore. I followed the rule of thumb that 87silverbullet outlined. On my FI build, I'm using 4.160 inch gaskets at slightly thicker thickness.

6togo

iTrader: (13)

Well i was looking at Cometic gaskets for the LSX block and they have them in 4.125" and 4.185" and GMPP has them in 4.200" will the exact size gasket of my bore work and should i stay away from Cometics i hear they are hard to seal up?

Briou

iTrader: (1)

You generally want a touch of clearance between the size of your bore and your head gasket....on my 454 LS3 i have a 4.185" bore and my gasket it a 4.205"...I went with Cometic and plan on using copper spray to aid in sealing, but they generally seal perfectly if the block and head are properly machined....

6togo

iTrader: (13)

Its a brand new LSX build from LME and new Mast 305 heads but i know Cometic recommends a certain finish! I just dont want to be yanking heads for leakage!
I think the 4.185" gaskets are the next size up though which will be .060 bigger than the bore wonder what affect on the comp that will have?

GasTiresandOil

iTrader: (2)

Why would you go for off the shelf gaskets that might not be the right size for your application? Call up Cometic, talk to them about your set up and have them make you up a set that fits your application. The difference in price might be $10 a gasket to have custom ones made for you.

6togo

iTrader: (13)

Truth is i did not know they do custom gaskets i will hit them up and see what they say!

A.R. Shale Targa

iTrader: (2)

Copper spray and pull the fasteners up in three stages. For example if the final torque is 70 ft./lbs.; I'd start at 40 and go through that sequence twice. Then up to 55; then final of 70.

6togo

iTrader: (13)

I seen some guys do the copper spray with the Cometics i sent them a email asking about custom gaskets if they are to high i may just go with the 4.185" ones just wonder what they will do to the comp. ratio being .060 bigger

87silverbullet

iTrader: (11)

It should only be a tenth or two of compression. Use this calculator.

http://www.csgnetwork.com/compcalc.html

Briou

iTrader: (1)

I just went back to my CR calculation work sheet and added 0.06" to the bore of the gasket and it made my CR go from 12.02 to 12.024....but that was with all the measurements from my 454 build

87silverbullet

iTrader: (11)

I just did the math and a 4.125 bore with a 4.000 stroke and a -3 cc piston with a 0 deck and a 70cc chamber with a 4.155 bore gasket, the compression came out to 11.387:1

When I kept everything the same and changed the gasket bore to 4.185 the compression went to 11.367:1 . I don't see where that would make a difference at all on power production.

Briou

iTrader: (1)

Yeah that is a minimal drop...I would run it...

6togo

iTrader: (13)

Yea thats nothing to talk about but i did chat with Cometic today they said they will make any gasket size i want no extra cost and it takes about 3-5 days!
So should i do 4.155" gaskets that would put them .030 bigger?

87silverbullet

iTrader: (11)

If it's no extra cost, I would go with the 4.155 gasket.

If you want them quick, summit has a 4.150 cometic gasket in stock ready to ship today

6togo

iTrader: (13)

I'm not in a rush now i'm thing about using the .040 gaskets to bump the comp. up a bit i waiting on some details from the builder but they should put me around 9.7-1 vs 9.5-1.

cmac06

iTrader: (16)

I thought those MAST heads required a 4.2" gasket.

6togo

iTrader: (13)

What makes you think that?