i understand the effects of quench hight and the wanted .040 clearance but is it better to have a thicker or thinner head gasket with the matching deck hight to go with each one to get the .04

do the thicker ones blow out easier or something?

 

I don't believe gasket thickness itself, has a bearing on the quality on the gasket. With little question, thickness is not as important as the quality of the gasket itself. IOW, how well it seals, and it's durability are more important criteria to analyze. With that stated, choose a gasket with reputation for providing a good seal.

 

For stock LT1's the ultimate would have to be .015-.020 gasket thickness, but its not recommended for alluminum heads. gasket thickness does play a role on strength, thinner gaskets usually have a less chance of blowing out then do thicker ones since the gasket area is less exposed to the chamber. Only problem is you can blow a thinner gasket easier with alluminum heads if you go too thin since the gasket won't have much play for the alluminum to expand & contract at the coolant passages etc... I highly doubt gasket thickness will play a role with alluminum heads at the combustion chamber rings since when hot, both may move as they please.

 

Smokey and Lingefelter both discuss this in their books fairly well. The 0.040" statistic is the bare minimum both of them stated they would use on steel-connecting-rod bottom ends. They even warned about short-skirt pistons (or closely spaced rings) causing the piston to rock in the cylinder and possibly touch the head.

Quench ranges from 0.040 to 0.060 were considered ideal by those car legends... so I'm personally shooting for ~0.045 to 0.050 on my 383 build up.

Don't feel bad about hitting 0.050, it's still a good deal better than stock (which is an ugly 0.070 or so). With a typicaly LT1 having a piston-deck height of -0.025", a 0.025" gasket would be great. The Impalla gasket is 0.026, and Mr.Gasket has a 0.029" one as well.

If this is for a new bottom-end /engine, you'll probably want to change the piston-deck height to -0.005"... which you can do with either piston selection, or by machining the deck down a bit.

FelPro, Mr.Gasket, and the Impalla SS gasket all seem to work well on LT1's. Stay away from any metal shims (like the copper gasket) that are 0.020" or less if this is a daily driver... they don't seem to seal well when cold, although they are used in race engines without problems (since they're almost always run high temps).

 

Oh yeah, one more thing... I've read that faster piston speeds near TDC can help with this as well.

If you plan on using short rods (like 5.7" instead of 6" say) and reving high (7000 to 8000?) you may be able to run a slightly greater quench gap and get the same effect (better mixing / detonation resistance), although I've never heard or seen any numbers to support/deny that theory, it's just what I remember reading a few months ago.

This may help explain why it's possible to run leaner A/F ratios after peak torque occurs though. While the VE does drop off, people seem to be able to run leaner A/F ratios after peak torque than they can before peak torque even though the VE is the same... only the piston speed is different. I dunno, just speculation.

Anyway... shoot for 0.040 to 0.060 per Lingenfelter & Smokey.

 

What book did lingenfelter write? Thanks

 

John Lingenfelter: On Modifing Small-Block Chevy Engines..HP Books-1238

Smokey Yunick's: Power Secrets S-A Design 06-7

also try HPBOOKS-1253 by Dave emanual

My books are 5-20 years old but I am sure even if the part numbers have changed the info is still good