I have a friend with an LSx swapped RX7, he has recently purchased a T-Rex cam for it, and is worried about piston-to-valve clearance. While the numbers are tight, he was wondering if he would be able to run double head gaskets to gain a few thousandths clearance, and if there are any adverse effects to doing so. Anyone do this and have problems like the gasket(s) blowing out?

 

Bad idea.
Most MLS gaskets are around .051 compressed, so running two will add more than just a few thousandths.
Aftermarket companies like Cometic offer different thicknesses of gaskets that should allow you to gain the required clearance for your setup.
You will need to determine what the thickness is for the existing gaskets and then determine how much extra thickness you need to get proper PTV clearance.
Keep in mind that the pushrods may have to be replaced with longer units to keep the lifter preload correct.

 

The t-rex should clear safely (barely) as long as no mill, stock valve size and OEM ( .054 compresssed HG).

Bigger than I would go but should be badazzz for a lite little car

 

He did get the thickest OEM head gasket he could find, I think it said .054 compressed. He was just looking for a little more safety margin. I've looked over his heads, they look fine, shouldn't need anything except cleaning, so hopefully we can have it done before Christmas

 

Why not fly cut the pistons then?

 

He doesn't want to pull the bottom end apart. Me personally, I'm not big on the idea of flycutting pistons while they are still in the cylinder, but it has been done. I think his exact words were "If I'm pulling the engine apart, it's because I'm building a 408."

 

Hah ... 11.9 @ 118 wasn't fast enough