[Half-Inch Stud]

Ref. Note; we thoroughly enjoyed a 70 GTO stick car with a 2.54:1 posi rear. 1900 rpm on HWY

Any HWY RPM from 1900 to 2500 @ 75 MPH is an eye-opener joy.

[JLMounce]

Originally Posted by Half-Inch Stud

Ref. Note; we thoroughly enjoyed a 70 GTO stick car with a 2.54:1 posi rear. 1900 rpm on HWY

Any HWY RPM from 1900 to 2500 @ 75 MPH is an eye-opener joy.

100% this.

I originally built my firebird with a set of 3.73 rear gears with it's th400. "For the performance." With a 26" tall tire it was terrible to live with at any speed approaching 60mph. 65mph was 3400 rpm. As a result the car only ever got driven around town. Maybe 500-700 miles per year is all.

I got tired of that and wanted a more highway friendly ratio so I put a 3.31 in it because I still wanted the performance. It was better, but still not great on the highway. It didn't really change my driving habits with the car.

Finally I bit the bullet and did the 4l80e conversion. Now I drive the car everywhere, typically around 3000-5000 miles per year. With the overdrive gear I didn't sacrifice any performance, but now the car is absolutely at home at 75mph and a much more relaxing 2200rpm. The value for dollar of that one update is far and away the best thing I ever did to the car.

[VCho455]

I drove my 69 400 T400 GTO for over a decade with 3.55 gears driving 255/60/15's. It Is a perfect combination for the car. With a manual 3.73's will make stop and go traffic easier to deal with as well as launching the car without lighting up the rears. But it comes at the expense of the a higher highway RPM. However different tire diameters can make the two ratios very similar.

The link goes to a great gear ratio calculator which allows a person to make detailed comparisons of drive ratio changes. Have fun!

https://www.blocklayer.com/rpm-gear

With a RAIV cam, Rhodes lifters, home ported 62 heads it ran 12.9 's shifting at 5500 and crossing the line finish at 5700 rpm. I also drove many road trips at 70mph without problems. But I'm not afraid to run 4000 rpm for hours like many folks. The first Pontiac I was around was in high school. My buddy Mark had a 68 GTO, 4.33 geared 4 speed and we drove all over North Idaho in it.

Lots of opinions on subjects like this and mine along with a sawbuck will get you a steaming hot cup of Joe just about anywhere. 🙂