Well with the trex cam and 5k stall/3spd you really have no hope of getting better than maybe 12mpg in that car. If you were serious about getting better mileage out of that car you would at least go with a 4l80 trans with a lockup converter. That could get you back in the 20+mpg range since your car is mainly a nitrous car when the nitrous is off it should still get reasonable mileage.
I originally defended you thinking that you were actually serious about trying to improve your car's mileage. I used to hang around on ls1tech but gave it up when I realized there was a huge amount of idiot kids on that site that think they have the ultimate car and everyone should worship them for dumping massive amounts of money in a small block v8 to make it fast. If you can't handle people picking on you on a message board about mileage when you don't act like you seriously care about your car's mileage then you might need to grow up a bit more and come back here when you are more mature and ready to take it all in stride and use the knowledge you gain to actually improve your car. Once people see you are serious about getting better mileage they will actually help you as much as they can.
If you only care about fast cars then all I have to say is my kit car will always be faster than your Camaro no matter what you do to it
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