My 92 Trans Am gives me only 14 miles to the gallon. I havent done much to my car, its pretty much factory stock, I am thinking of having a performance Cam shaft with new lifters, push rods and may be injectors. I know all this is going to give me kinda more power, but I am wondering how bad is it going to affect my gas mileage. If U have done a Cam shift job let me know how bad did it affect the gas mileage, I dont want a performance Cam in my car and only getting 6 or 7 miles to the gallon. Also is it advisible to change injectors for high performance or not??

 

Most stock 305s get 17 or 18 mpg around town. You need a tuneup for starters.

A performance cam will likely eat into your mileage, alright. Maybe a couple miles per gallon, depending on how radical you go. I can't see any 305 only getting 7 mpg, though.

My 305 gets 14 to 16 mpg, depending on the season. Winter is worst by far.

 

A mild cam shouldn't hurt mileage whatsoever. I used to regularly get 26mpg on the highway in my old 85 Z28 with a mild 350 with a 270 cam in it. I've only seen that number twice out of my 92 on long drives, so much for EFI and smaller stock engines being good for gas mileage.

But sitting bull is right, there is something wrong with your car as it sits now (or you just drive with avery heavy foot). A stock 305 TPI should easily get closer to 20mpg in town and 24+ on the highway. If you can't even get optimal MPG out of a stock engine, no telling what you will do to a modified one.