245-50-r16 sorry ya i figured that out when i took off.. i did the test 5 times and the MPH is 36-38 and everytime was a hair over 6 grand id say 6200

 

6200 rpm in first with 4.10 gears is 37.7 mph.

4.10 gears in OD at 75mph would be about 2850 rpm.

My guess: You have 4.10 gears, and your speedometer and tach are both horribly miscalibrated.

 

wow your smart ha. well how do u go about calib the gauges?

 

I don't have much experience with LT1 cars, so maybe someone else can chime in here. You can calibrate the speedometer by getting a tune. Around $150 will get you a mail-order tune from someone like MadZ28 or pcm4less (both are supporting vendors of this forum). However, since the previous owner modified the car and you don't know what's been done, that might not be the best choice. A real dyno tune would be best, but that could cost as much as $500.

I don't know if the tachometer is tunable. AFAIK, most people who care about knowing the exact RPM buy a dash-mounted tach from AutoMeter.

 

thanks. i have a buddy with a shop up in Sioux falls, SD that has a dyno and everthing and has a killer price to run on it so maybe i should just venture up there and take her in.

 

Depends on how hard you're getting on the car.

 

WOT.

 

This may help:
http://www.f-body.org/gears/