[liquidzorch]

Hello. I understand that at a higher altitude there is less air density, so compression in the engine reduces, and this in theory, should give less mpg. Which is why I think my car is not getting stock mpg.

I am at 5000 feet above sea level and on a compression test I get 150 psi all across, at sea level that would be 180 psi. Which is good compression for my engine (d15b7).

Now my engine is all stock, no mods, almost every sensor new, and engine just rebuilt a year ago.

I am thinking of milling .040 off the head, and use a d16xx head gasket. This should give me a higher compression ratio. from 9.1:1 (stock) to about 10.1:1.

Now at my altitude, those numbers would be about 8:1(stock) and 9:1(milled). So it would be like getting back the power I have lost at this altitude.

This project is for better gas efficiency. Is this idea good? It is a low cost project that in theory should give me better mileage.

Any suggestions? Am I wrong in thinking it will help mileage?