Okay, I've posted this in the 6.2 forum as well but I imagine I'll get an informed answer here! I've done the searches and there is some info but those threads are locked:mad:

My Hummer H1 desert racer has 6.2 engine that I have installed a WHipple supercharger on. It has a arctic milpec mechanical 6.5 IP and 6.5 injectors.

I've ordered a set of ARP head studs and new felpro head gaskets. I'm planning on turning the stock boost (7-10 lbs) up to about 10-14 lbs-ish by installing a slightly smaller pulley on the supercharger. The gaskets I've ordered are the .010 thicker sets. Since I'm taking the heads off to do the studs (body is already off, now is the time!) anyway, is there any reason I should not double up the .010 head gaskets to give a total of .020 and gain lower compression? Heck, maybe I ought to toss the pair on top of the stock size Felpro gasket already on (less than 10K miles) for a total thickness of .025 - ish?

If your interested in the truck and its details, the website is

http://scaryfasthummer.googlepages.com (http://scaryfasthummer.googlepages.com/)

It wont work or wont work long.

Okay, I'll bite: why, specifically....?

Double headgaskets will not seal very well against each other, and you would change the valvetrain geometry by raising the heads.Also may cause intake bolt alignment issues. Being an IDI engine injector spray angle would not be affected but all in all, there is lots better ways to decompress.

The above post is right. Also think about how much pressure is contained inside the cylinder. It can’t escape through the cylinder wall or the head because of their strength. The gasket is the weak point. Start stacking them up and you are multiplying the amount of weak surface area and you are asking for a leak.

The above post is right. Also think about how much pressure is contained inside the cylinder. It can’t escape through the cylinder wall or the head because of their strength. The gasket is the weak point. Start stacking them up and you are multiplying the amount of weak surface area and you are asking for a leak.


Thanks, that was helpful. How about just one .010 gasket? Do you see any dramas with that? I'm asking because while power is one thing, reliability is the key to my type of racing. Blown headgaskets in the middle of a thousand miles of sand dunes is NOT an option!:eek:

Assuming your not intercooled you can run all day long at 10-12PSI with the stock compression. I've towed thousands of miles at 15PSI on stock compression.

The .010" over gaskets will lower the compression about 1 point. Some believe the thicker gaskets increase the surface area and hence the outward push on the fire ring, which is true, but I've not heard of any issues. I'd say with studs you'd be fine.

Assuming your not intercooled you can run all day long at 10-12PSI with the stock compression. I've towed thousands of miles at 15PSI on stock compression.

The .010" over gaskets will lower the compression about 1 point. Some believe the thicker gaskets increase the surface area and hence the outward push on the fire ring, which is true, but I've not heard of any issues. I'd say with studs you'd be fine.

Extremely helpful! No, not intercooled; blower mounts right on top of modified intake manifold. If you've got a clue how to make an intercooler (or charge air cooler, whatever) between a supercharger and the manifold, I'm all ears. I do plan on going with the 18:1 pistons and girdles when I pull the engine out next time as thats major surgury. I suppose I'll get the splayed main caps while I'm at it. Right now I just want to edge the boost up slightly and keep it all together.

Thanks heaps!

If you've got a clue how to make an intercooler (or charge air cooler, whatever) between a supercharger and the manifold, I'm all ears. Thanks heaps! Water/methanol Injection, maybe. just an idea. would haveto carry alot of water, potentail weight issue for long dessert races i guess.