I am driving on the freeway at 70 m.p.h. and the tach shows 2,300 r.p.m.

Please help me determine what the ratio is on my new gear. Seems like a

3.08 or maybe a 3.27 gear ratio?

Thanks for your help!

 

Im confused as to the title of your thread but ill try to answer the question. I have 3.27s and my rpms are around there or a bit more so the only true way to tell is get under it and spin the wheels. Best way i found is have a buddy spin one of the wheels one revolution. Just a hair more than 3 turns of the pinion is a 3.08, a quarter more is 3.27. Also there is no such thing as a 3.42 9 bolt. It is a 3.45. Im not sure any of that really helped you but if you have a 9 bolt then yes you are correct in your guess. It is either one of those two.

 

You are correct, it is supposed to be a 3.45 gear ratio. Sorry.

I'll try what you suggested. Thanks.

 

Look at the size of your tire. It will probably be a 245/50/16. If you want to be really precise, go to www.summitracing.com, type in the make and model of the tire, and get the specs. Each manufacturer's tire is slightly vaired in height.

Go to this site;
http://www.car-videos.net/tools/speedrpm.asp

Type in all of youre info.
3.06, 1.63, 1.00 .70 for 1st, 2nd, 3rd, 4th repectively, and see what the Speed vs. RPM says on the chart.

You'll have to guess what the rear end ratio is. Try 3.08, 3.27, 3.45. If those dont work, there are a few others you can try for a 9 bolt.

Next time youre on the freeway, cruise along in 4th, and make sure the torque converter has locked up. Just notice what the RPM's are and see if they match your calculations.


According to my calculations, asuuming your TC has locked, and you run a 245/50/16s on the rear;

3.08 = 2050rpm
3.27 = 2180rpm
3.45 = 2300rpm = 70.1mph

You most likely have a 3.45 rear gear.

 

online170----Thanks for making it easy for me. Looks like you're right. I feel better now. Look for my other post on Vendors.