I went by the Kirkland Mazda dealer today to look over the CX-7 and collected a brochure. Before I actually buy one to experiment with/on I was wondering if anyone in the Puget Sound region might be willing to participate in an experiment to improve the FE of the CX-7, possibly substantially so.

What I would like to do is mill the head of a CX-7 engine to get a compression ratio of 12:1. 12:1 has become typical for a DFI, Direct Fuel Injection, engine, but since the CX-7 is turbo charged the factory's "native" compression ratio is, as it must be, quite a bit lower in order to provide for the additional "compression" from the turbocharger as it spools up.

During the experiment the wastegate would have to be "wired" open so the effective compression ratio could not rise (much) beyond 12:1.

If anyone owning a CX-7 is interested I would be will to pay the costs purchase and install a new factory head once the experiment is complete.

I suspect the off-boost FE improvement might be in the range of 50%

 

I would not recomend any mods on a turbo car. If you do mazda will brand the car. [ NO WARRENTY] Mazda has spent alot of money,time making this car. They know what works. The turbo runs at aprox 15 psi. The turbo is controled by the pcm. The FE system runs fuel pressure anywhere fromm 400 psi to 1800 psi. You have a very good chance of destroying the engine. If the car is out of warrenty then do what you want. Good luck Kevin

 

Yeah, that doesn't sound like such a wise mod to tackle on a brand new DD. Besides, if you increase the static compression only to reduced the boosted compression, what would be gained? A little more low end maybe? I'm asking 'cause I'm really not sure.