Thin Head Gasket and Comprtession Ratio

[Ronno6]

If the 1-piece pan gasket comes off without any damage, you can reuse it.

Unfortunately, I used gasket sealer-the black silicone stuff- and had one heck of a time getting the pan off...the gasket is toast!

 

[Ronno6]

When I added Blueprint aluminum heads to my SBC crate the 64cc chambers increased compression, but I also used the Mahle 5746 gasket (.025") to get just a little more compression. Those gaskets were recommended by several guys on the hotrodders board, and they seems to be working well.

With my stock crate pistons, 64cc heads and thinner gasket, I'm probably only at about 9.4 compression, so it runs on any type of gas. However, its a lot better than the original ~8.2 compression of the GM base crate engine.


Bruce

Once the main parameters are set: bore, stroke,piston, and combustion chamber volume, the variables: deck height and gasket thickness are proportional for quench and C/R.. That is to say, the thinner the quench zone, the higher the C/R, and vice versa. If quench is set to the optimal range, the only way to otherwise affect the C/R is by varying the combustion chamber volume (given flat top pistons.) Dished pistons, I would think, would affect the quench. Domed pistons would affect the combustion chamber volume.

 

[WHEELMAN]

Am I wrong.at 30 over.thats it for the block.or can you go 40 over.i would use the best head gaskets you can get and seal it up tight.new head bolts intake bolts and torgue it right..maybe use some red loctight too.

 

[MikeB]

Google "quench height" to understand its importance.

I use these head gaskets a lot:
GM 14096405
Compressed thickness is .028"
They are composition gaskets, so are more forgiving than steel shims.

Use an assembly lube like this on head bolts, not Loctite! And don't use any sealant on the gaskets.

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[Ronno6]

As long as the 0.012" cleaned up the decks, I plan on using the Fel Pro 1094 steel shim
gaskets. They are .015" thick and coated on both sides in order to achieve a good seal.
The heads are new aluminum; new ARP head bolts to be installed with teflon pipe sealant on the threads and the Ultra Torque lubricant applied as directed, properly torqued as usual.

WHEELMAN, I'm not sure what dimension you are referring to when you say 30 or 40 over.....I probably could have had .040 machined from the decks, but that would have limited my gasket options. As it stands, I have asked for .012" off, giving me piston deck height of .028" in the hole combined with a .015" gasket for .043" quench. If the decks didn't achieve suitable cleanup at .012", I can have more shaved and use thicker head gaskets.

 

[rt66paul]

I would consider using another cam. You engine will never perform the way the cam was designed and you won't be happy. There are a few performance cams with more low end that will really do the job. Always match your parts as they are designed - having a good squish is important, but not as much as a good match on compression and timing.

 

[Ronno6]

I would consider using another cam. You engine will never perform the way the cam was designed and you won't be happy. There are a few performance cams with more low end that will really do the job. Always match your parts as they are designed - having a good squish is important, but not as much as a good match on compression and timing.

Thanks, but I dunno. This guy used the same cam and a set of Vortec heads and produced over 400 HP:
http://www.superchevy.com/how-to/67838-budget-vortec-head-cam-355-build/
My C/R (10.0:1) will be a bit closer to that of the LT4 (10.4:1) the cam was designed for, and my aluminum heads should flow more air and be better suited to higher compression.
I think I'll give it a shot..........

 

[4WDKC]

Thanks, but I dunno. This guy used the same cam and a set of Vortec heads and produced over 400 HP:
http://www.superchevy.com/how-to/67838-budget-vortec-head-cam-355-build/
My C/R (10.0:1) will be a bit closer to that of the LT4 (10.4:1) the cam was designed for, and my aluminum heads should flow more air and be better suited to higher compression.
I think I'll give it a shot..........

While we are on the subject of what the cam was designed for, it was for use in a 3500lbs fbody and corvette with 26" tall tires and 3.42 gears and a stall converter, not 4500lbs trucks with 308 gears and 31" tall tires. Are you sure this cam is going to do what you need it to do in your truck?

 

[Rusty Nail]

My f-body has 2.77 gears!

 

[Ronno6]

While we are on the subject of what the cam was designed for, it was for use in a 3500lbs fbody and corvette with 26" tall tires and 3.42 gears and a stall converter, not 4500lbs trucks with 308 gears and 31" tall tires. Are you sure this cam is going to do what you need it to do in your truck?

Near as I can figger my C10 Stepside weighs 'bout 4000#
The original 2.73 open diff has been replaced by a 3.73 posi turning 29" tires.
My Muncie M20 has a 2.56:1 first gear.
I also have the ultimate stall speed device...a clutch!
I think I'm good...........

 

[bucket]

Near as I can figger my C10 Stepside weighs 'bout 4000#
The original 2.73 open diff has been replaced by a 3.73 posi turning 29" tires.
My Muncie M20 has a 2.56:1 first gear.
I think I'm good...........

Yep, you should be fine. When my stepside was still a small block, it came in right around 3800 lbs on a certified scale.

 

[Ronno6]

I think if I had left the C/R at 9.25:1 then I WOULD have been disappointed with the performance....

 

[Ronno6]

Picked up the block today.
All is good.
Twas a good thing to have done, as the banks were a tad out of square and not quite flat.
Perfect now from a dimensional standpoint.

 

[MikeB]

As it stands, I have asked for .012" off, giving me piston deck height of .028" in the hole combined with a .015" gasket for .043" quench.

Perfect! I have used .043" quench with 9.005" deck/.038" gasket and 9.015" deck/.028" gasket. Have run as much as 9.4:1 compression with that quench height with no detonation, even with iron heads and small cam (204 intake duration).

Just don't assume current deck height is 9.025". More important to tell the machinist the final deck height you want rather than how much to remove.

 

[Rusty Nail]

Y u no haz pix?