Got an 1985 cutlass salon, has a brand new 355 bolted to a th350 transmission. Right now i believe the stock gears are 2.41:1 somewhere close in that neighbourhood by my calculations. running 245/60/R14 tires on it that stand 24" tall in total. last gear is 1:1 i believe with this transmission. I do drive the car daily and on the freeway at 60-65mph for no longer than 30 minutes at a time. the car runs very cool and turns over 2700 rpm at 65mph. I would like to throw a quicker gear in since i have no concern for gas mileage and want to have a little more horses on hand when i drive. i am running a stock volume oil pan and stock volume pump as well, engine water temp runs at 150-160 on hot days. What would be a good gear to upgrade to without inflicting more than necessary harm to my newly built motor? thanks

 

stevo,

Those numbers you gave just don't jive. I think you have a higher ratio than the 2.41. Your RPM's seem to high for that speed. If your rear end doesn't have a tag, you could take a look at the Ring and Pinion and do an accurate count on the teeth to be sure. Then find a Gear Ratio Calculator, to calculate your appropriate RPM's. So, what I'm saying here is, you really need to know exactly what you have now, before you change.

Also, I think you need to check your Thermostat, or do an actual temperature reading from the top of the Radiator. You really need to be operating at a higher temperature to get the best out of your engine. Probably around 180-195°.

 

do you think i have a higher or lower ratio? i have stock torque converter soon to be replaced could it be my old t/c is slipping?

The car has a 160 degree thermostat because i thought 190 was causing a knock i later found was not from heat i could put the 190 back in.

 

1) That's what you need to find out. Check if you have a Tag telling that, or, if you have a Plate, just remove, count, and put fresh Grease back in.

2) IF you Converter is slipping, then it should be repaired at some point, but, you can still check the rear end ratio in the mean time.

3) You should use the recommended temperature Thermostat. Engines are designed to operate at a certain temp.

 

Jack up the rear of your car, rotate the rear tire one complete rotation while at the same time counting the rotations of the drive shaft, this will tell you your gear ratio. I agree with SWHouston, your numbers don't jive.

 

Yep, that's another way to do it too !
But, put some nice clear Chalk marks on your Driveshaft and Tire where you can clearly see where you are at on the rotations. Use your Drive Shaft to turn the Wheel, not the other way around. Should repeat that a couple times to be sure. There are several ratios which are real close to the other, so do it carefully.

Possible...
2.73, 3.08, 3.23, 3.42, 3.73, 4.11, 4.30, 4.56... see what I mean.