Thinnest gaskets are Mr. Gasket 1121G. 0.027" - 0.028"

Everything else is thicker.

MP sells a similar (maybe the same) gasket. Check prices as the Mr Gaskets come one in a package so you have to buy two. At one point I got the idea the MPs were two to a package, but they're not always available.

Dave, totally closing both intake and exhaust valves turns the cylinder into a big air spring. Since nothing is being pumped, no work is done. There are losses though, first is friction and second is, some of the heat of compression has to leak out into the cooling system. There is also something called hysteresis which means that some of the energy required to compress the spring isn't regained when the spring is unloaded. I think this component is negligible.

When one starts looking at articles in the Journals of the Society of Automotive Engineers, it becomes clear that EGR is very common, but since the advent of variable valve timing, it is easier to get EGR by adjusting the exhaust opening and closing events. The final product engine is the result of probably thousands of runs of computational fluid dynamics, dyno tests, and actual street driving.

The computer is programmed to give the engine the best combination of air, fuel, spark, etc. which will still be working well enough to pass an emissions test after 100K miles. Tuners are able to gain power or efficiency by reducing the safety margins.

R.