I was talking with my dad and he said for the stock 3:23 gears that should be in my 1997 Z I should be hitting around 2k RPM at 70mph. I was wondering if this is about what anyone else was getting or not? I currently hit about 2200-2300 at 70. When talking with him he said it could indicate they arent stock gears. Just a curious question so if anyone knows thanks for the answers.

 

My 4L60E calculator shows (assuming 245/50-16 tires, and 4th gear) at 70 MPH with 3.23's, you will be turning 2,062 RPM

The stock tach typically reads 100-200 RPM higher than actual engine RPM. You need to read the true RPM off the PCM with a scanner to get an accurate reading. Tire diameter will also affect the RPM. What size tires are you using in the rear? How worn are they? Are they inflated correctly?

If someone had swapped in 3.42's, the RPM would be 2,184

 

Rear tires are 285/35R18 atm and have a good amount of tread. They are currently inflated to 40psi.

 

With that tire diameter:

-3.23 = 2,050 RPM

-3.42 = 2,171 RPM

Why are you running 40psi in the rear tires? Wayyyyyy too much. Inspect the center of the tread for excessive wear. You're not looking at the max inflation pressure on the sidewall of the tire to determine the inflation pressure? You should probably be closer to 32psi.

 

The max PSI for those tires is 51PSI. I put it at 40 to be somewhat in the middle of what the car says it should have vs the tire itself.

So if im hitting 2300rpm on the tach most likely the gears are 3.42?

 

Did you read the part about the stock tach reading higher than actual RPM? Or are you getting the RPM from a scanner?

 

Yeah I read that it could be 1-200 higher. I dont own a scanner and cant afford one. Was going off of if the 3.23 would be slightly over 2 and Im getting right at 2300 it could most likely be the 3.43. Just going off a guess.

Being my tired a rated for max of 51psi do you still think the 40 is too high or should I drop it down to 32.

 

I've run the stock 245 tires at 36psi, my 275's at 34psi and 315's at 32psi. The wider the tire, the less pressure needed to support the vehicle.

Rather than guess at the pressure, try varying it to see which pressure gives you the best traction. At 40psi, you may be giving up quite a bit of traction. And as noted, check the center of the tire for excessive tread wear compared to the edges. That it a sure indication that you have them over-inflated. Unfortunately, by the time you can measure the excessive tread wear, the damage is already done.

 

Thanks injunner