itsMikey

what the hells wrong with my car?

Sonix

iTrader: (1)

city mileage? Driving it relatively hard? Sounds pretty normal... Pure highway, with the cruise set at 65mph, you can do much better - but otherwise that's life.

Marv02

I get about 8 to 10 city semi lead foot 24 to 26 HWY at 65 to 70 MPH.

383 with lt4 Hotcam 307 gears

Orr89RocZ

iTrader: (20)

Wow my twin turbo gets 13-14mpg mixed driving and its not even tuned 100%. My old L98 and 383 were both around 16-17mpg city and 24mpg highway.

If not already done, make sure you have fresh plugs/wires/o2 sensor/no exhaust leaks, and clean air filter/fuel filter/etc. It should do alittle better than that

itsMikey

this was pretty much all freeway for the night but i was cruising at 80 the whole time..70 seems to be my optimal speed with the gears i have..gonna try that next time i drive there..

my college is about 40 miles away give or take detour routes of 2 or so miles..

im not hard on it in the streets either tho most of the time..i mean ill put my foot into it to get around someone or pulling out but usually i wont shift above 2k.

Thirdgen89GTA

iTrader: (5)

My LT1 gets 19mpg hwy with no OD, and no TCC lockup. This is with an average cruise RPM of 3000-3500rpm. Around 70mph its about 3000rpm or so.

http://www.youtube.com/watch?v=xaCbhLoNaJ4

If I drove it daily it would be about 17mpg. Really needs OD, or the 6spd swap. Stupid PCM and harness doesn't match the year of the trans. Trans wants PWM TCC Lockup. Harness doesn't support it. I could re-pin it, but I'd have to yank the harness out of the car to do it right. So instead, I just drive it as is. I already have a rebuilt T56 waiting in the wings and its not may daily driver. So I don't care about the lack of OD and TCC Lockup as much.


Yes, I needed to shave in that video.

_______________________________

Have you done a tune-up? Is the coil weak? Plugs/wires new? Aka, have you covered the basics?

1MeanZ

iTrader: (9)

Interestingly I've been a bit dissapointed in the mileage from my GTA as well. The car has lots of new stuff and seems to run very well, but it only gets 19-20mph highway at best. It's gotten as low as 17. I've even gotten in the tune and leaned out highway mode and it seemingly hasn't done anything. I've datalogged it and I can see that it goes in, but the car still gets 19mpg. The fuel pressure is good, the O2 sensor is new as are the plugs, wires, cap and rotor. This is on a 30 mile commute each way to work at 70mph. I still need to check the plugs but it sure seems to be running nicely. Only other items that come to mind are that the previous owner installed a high pressure and volume oil pump (which is a waste on a stock motor) and it has a quiet gear drive on the cam (which is also a waste and will be coming out this winter). The gear drive does not appear to be setting off the knock sensor at part throttle.

I see lots of L98 IROC guys with 2.77s claiming 22-24mpg. My LB9/T5 2.73 geared 91 TA got 26 on a regular basis. Could it be the 3.27s in the GTAs are really hurting mileage that much? Normally I wouldn't think that is true, but I'm running out of ideas with my car and it still gets about 4mpg under what it should. Unless my speedometer is off somehow....

This winter I'm pulling the engine to replace the oil pump, gear drive, valve seals, and swap a T56 in. Hopefully after all that I can be in the mid to high 20s on the highway.

shortyskater

My stock 87 iroc was getting about 18-20 mpg mainly city driving before I took her off the road. Only recent tune up was plugs. I'd try a tune up. It is a sports car. anything better than low 20's mpg is considerd good. But, did you really buy your car to be a economic ride? Might as well own a Prius if your looking for that.

Thirdgen89GTA

iTrader: (5)

There is nothing wrong with having your cake and eating it too! You CAN do it. You just have to be smart about it.