Compression ratio HA vs IC

[Jerryl]

What is the stock mechanical compression ratio of a Hot Air vs an IC block? Just need to verify what I "Think" I know.

Anyone know the cam specs so I can get an idea of the dynamic compression ratio's?

 

[cool 84]

Compression should be the same. Hotairs had a taller deck but used a thinner headgasket to make up the difference. One member did an actual compression test on a few factory motors and stock was 7.9.

 

[Jerryl]

Thanks Cool 84!
Thought the IC car was 8.5 : 1??
(Good thing I asked)

Any idea at all on cam specs between a HA and IC?

 

[boostmaster]

cam

Stock cam specs are the same from 84-87.

 

[Turbo Riviera]

With one exception Boostmaster...

The turbo Riviera motor had a weaker cam than the Regal.

 

[racemybuick]

yeah....i remember reading all turbo regals were 8 and a half to 1. the riv was a little diff.

john

 

[Jerryl]

If a 109 block is used in a hot air, what gasket thickness is required to get the correct installed height for the stock compression, and, will the pushrod length be correct with a "double metal - hot air" gasket?

 

[6SENSE]

headgaskets

Why not use the GM stock headgaskets for 86/87? They are still available from dealer as well as vendors and will give you the correct compression ratio (gasket thickness for 86/87 gasket is something like .060 thick when compressed).
Pushrod length will not be an issue this way either (depending of course on your cam).

 

[Jerryl]

6Sense,

Good idea!
Just thought that most use the double metal Hot Air gaskets in a 109 block since these are pretty much buller proof but not sure about the other stuff.

Maybe for a hot air running 12 - 20 PSI boost blowing the stock head gasket is not an issue (??)

 

[6SENSE]

Would you rather have a blown head gasket or a blown piston? Some people look at the head gasket as a fuse. If it blows something wasnt right. You change the headgaskets and address the problem that caused it to blow. If all is right and your using a scantool and taking the time to tune, you shouldnt have a problem.

Plus those GM headgaskets are good. Ive run them on a couple of blocks that I beat up on and never blew one (high boost 25psi+/-).

 

[Jerryl]

Good point!
Thanks!