what makes gas mileage go down more, a cam or a stall.... cant you do anything that raises gas mileage without taking away power?

 

A cam can add milage if it's matched to the flow of the heads, volumetric efficiency. Basically anything that can make the vehicle breathe easier AND is tuned in accordingly will economy. It takes less work to make the same power. I gained ~3mpg in my F150 with all its mods...that's still untuned also...it averages 16.5mpg on the freeway now and about 14.5 overall. Rememeber it's got TERRIBLE heads on it that restrict power and efficiency as well as a cam that's too small.

The tune I have added milage to my Z.

I think Tiburon picked up ~2mpg with the mild 212/218 he's got...

But as I stated, it's all in how you drive. I average 15.5-16.5 in my Z71 and get almost 20mpg on the freeway...I drive 65-70mph and have 33" tires w/ 3.73:1 gears...I lug on the freeway. I bet if I had some 4.10:1 gears to get my cruise RPM to 2100-2200 I'd pickup 1-2mpg.

Also keep it running in tip top shape... plugs, PCV, fuel filter, etc.