[64speed]

I have the TKO600 with the .64 overdrive 3.70 gears and a 26 inch tall tire. The speed limit thru town is 30-35 at which of course I drive in 4th but on the side road home the speed limit is 50. Once I get some speed and RPM up I can shift to 5th at 45 mph and never lug the engine or lose my ability to gain speed. Engine rpm in 5th at 45-50 is just above idle. I feel like my rear gears are a little too deep to be ideal but it makes it really easy to take off and drive 1st is just a little short. When I went to the beach in March I put 22 gallons in the tank and drove 232 miles to the hotel (interstate 90%) and then drove around Myrtle Beach when I got there another 25-30 miles and I still had about 3 gallons. The TKO and the RTX gauges are the best upgrades to the car I have made.

[Formulajones]

The most popular package I've done here is the tko with a .64 and 3.73's.

I've done them with 3.50-ish gears as well. In Fact our daily had 3.55's with a .64 for a few years and it was fine, used it all the time at 35 mph.

I've since put the original 3.73's back in the Z so I could use the 3.55's in another project and quite honestly I can't tell much difference in overdrive. Darn thing got 22 mpg on the last trip with the big fat 780 Holley on it cruising at 75 mph lol.

[scott70]

I’m going to do the 2.87 / .81 OD. With my driving style , 3.31 gear and 255/60-15 tire I think it will be good. It’s about a 500 rpm drop from 4th to 5th which is good enough for me.

[jhein]

Originally Posted by scott70

I’m going to do the 2.87 / .81 OD. With my driving style , 3.31 gear and 255/60-15 tire I think it will be good. It’s about a 500 rpm drop from 4th to 5th which is good enough for me.

That is the exact combo I have. Same trans gears, rear gear and tire. As I recall, you and I both rarely if ever drive at Interstate speeds. 55 mph is really the highest speed limit I encounter. The .81 OD is perfect for 65 and even 70 mph cruising. Even 75 mph @ ~2500 rpm is still very comfortable.

[scott70]

Originally Posted by jhein

That is the exact combo I have. Same trans gears, rear gear and tire. As I recall, you and I both rarely if ever drive at Interstate speeds. 55 mph is really the highest speed limit I encounter. The .81 OD is perfect for 65 and even 70 mph cruising. Even 75 mph @ ~2500 rpm is still very comfortable.

Yes,, most highway driving around me is a 60 mph limit which means I’ll be cruising 65. If I hit the interstate ( rarely) it would be 75 and like you said that still manageable .

[Formulajones]

That's a lot of money to spend for a small gain. If you guys are really driving that slow (55 mph) why are you even looking at overdrives? For as little as you drive these cars and cruising at the old speed limits I wouldn't even be thinking about an overdrive.

[jhein]

Originally Posted by Formulajones

That's a lot of money to spend for a small gain. If you guys are really driving that slow (55 mph) why are you even looking at overdrives? For as little as you drive these cars and cruising at the old speed limits I wouldn't even be thinking about an overdrive.

Well, for a 55 mph limit I will go up to 65 (my local LEOs ignore that here and in most places I think). That's around 2700 rpm in 4th gear vs 2150 in 5th. That's a pretty big difference. Plus you also get the 2.87 1st gear, that turns my 3.31 rear into the equivalent of a 3.77 when compared to a Muncie with it's 2.52 1st gear. It works for me. Your driving habits are different and if I used my car like that I'd most likely get the .68 too.