i just got back from a little road trip and right off the bat i noticed that on the interstate @ 75MPH my car was runnin about 3400RPM is that high. i dont know if this car has different gears and i am the 4th owner of the car so the previous owner does not know either. any feedback would be helpful thanks

 

What kind of car is it? We'll need to know the year, model, engine, and transmission (auto or manual).

My 2002 Z28 M6 runs 75mph at a little under 1700 rpm.

 

oh yeah sorry about that .its a 94z auto

 

Does the shift lever on the console allow you to select "1"?

 

yep aftere i noticed that it was really high i took it off the interstate went through all the gears. everything is workin fine.

 

I'm not asking if it's working -- I'm asking if it's an option. Some auto cars only allow you to go as low as "2", and that's an indicator of which rear-end gear ratio your car came with.

My guess is that it's not shifting into overdrive.

 

What he is getting at is if it isn't, that means you have the 2.73 rear end ratio. Another way to tell what rear end gears you have is look for the RPO codes on your driver door. GU2 means you have 2.73s, GU5 means 3.23. But even with 3.23s, 75 mph @ 3400 RPMs seems high. Are you running aftermarket gears? Does it seem like the engine is actually running that fast? If not, it could be your speedo is off.

 

yes it goes to "1" and the code is GU5. and i checkd the speedo on the way back with a friend was about 2-3MPH off of the 06 Gran prix. and idk if i have different gears. i might but i did not put them in and i have not checked it out at all..

 

and yes its goin into OD

 

So the only thing left is gears!

 

thats what i was thinking too i just didnt know if the lt1 ran that high on the interstate. i dont have any friends around here with lt1's so i couldnt just check with them so i just askd it on here

 

A stock GU5-equipped LT1 A4 in overdrive should run about 2200 rpm at 75mph.

Go hop in the car, go somewhere nice and wide open, and do an acceleration run until it shifts into second gear. Note the MPH and RPM when it shifts, and come back and tell us what they are.

If you have room, do the same thing for the 2-3 shift.

If my math is right based on 3400rpm in OD at 75mph, your gear ratio is about 4.9:1, which is absurdly high. I don't think they even make a gearset that high for a 10-bolt rear end!

What size tires do you have?

 

i have the stock camaro salad shooters. and what not.. ill go do that test a minute and cme back iwth the results

 

Not asking about the wheel size. The tire size. It's on the side of the tire. It'll be something like 245/50R16.

 

While we wait for him to come back... somebody tell me what the stock shift point RPM is on an LT1. 5700?