[Radman]

My Tempest is running a 389 Tri-Power, 700R4, Ford 9 inch with 3:50 gears, and the rear tires are Hooser 28x9.50x15. That is a 28 inch tall tire. 70 MPH is right at 2000 RPM. The 700R4 has a 3.0 first gear, so there is lots of grunt off of the line.

[Formulajones]

The other advantage with the 5 speed (and other overdrive trans swaps) is two fold, that no other swap provides.

The issue with the M22 and M23Z's is that you still don't have low rpm highway cruising. 70-75 mph is still going to be around 2800 rpm even with 3.08's out back so mpg isn't a big improvement. Yet you still don't get the first gear multiplication you get with a 5 speed either. Not to mention you don't save a lot of money in the process. The prices of those modified 4 speeds are pretty darn spendy. I haven't had a customer yet that considers it an option once they see the price differences.

With the TKO-600 overdrive, you don't need to be running a 3.08 rear gear. With 3.55's your highway cruising is going to hover around 2,000 rpm. And with the 2.87 first gear, the first gear multiplication is 10.18. An M23Z can't improve both ends of the spectrum like that. You'll loose one or the other trying to make one better.

[Formulajones]

Originally Posted by lust4speed

I'm planning on also purchasing a Strange Dana 60 (hell of a sale going on there until December 3rd) with a 3.54 ratio. So first gear multiplication will be 10.16 which should also be good for pulling stumps or clunking along on the 91 Fwy coming home from a show down in Tom S's neck of the woods.

That's exactly what I've preached for a long time here and I know we've had that conversation before. You'll love that 2.87 with 3.54's out back. I'm running it with 3.55's and it's about perfect. Waaaaay better than the old M-20's 2.54. The car suddenly became a pleasure to drive around town.

[tom s]

All 3 of my cars are right at 1800-2100 for highway speeds.I would never go back to 2500-3000!Tom

[track73]

I already had a 2.73 Camaro 10 bolt posi hub to hub rear end and a 3.43 First gear ST-10. I bought a cast iron case and had the gears cryogenic treated and now I have what amounts to a three speed with over drive. The . 030 over 455 has so much low end torque I didn’t think I needed a 5 speed. I can do 1000 rpm in 4 th in town or keep it in third. .

[Formulajones]

Exactly Tom , That's the part that once you experience it, you wonder why you didn't do it sooner.

Not just wear and tear and better mpg, but the noise level also drops considerably.

[Formulajones]

Originally Posted by track73

I already had a 2.73 Camaro 10 bolt posi hub to hub rear end and a 3.43 First gear ST-10. I bought a cast iron case and had the gears cryogenic treated and now I have what amounts to a three speed with over drive. The . 030 over 455 has so much low end torque I didn’t think I needed a 5 speed. I can do 1000 rpm in 4 th in town or keep it in third. .

That's basically what the M23Z swaps are doing. It works for some people. Personally I like the way you did it, it's better than an M23Z as far as gear ratio multiplication and a whole bunch cheaper. I've even mentioned the ST-10 swap in the past that's been a viable option since the 70's.

You're still turning rpm on the highway, and 1st gear multiplication is still only 9.36, but it's better than an M-20/3.55 setup.

[brooknice]

I run a gear vendor with a turbo 400 with 3.73 gears I plan on dropping the gears to 3.55 with the new engine coming in. I have had the gear vendor for 3 years no problem so far with it. Air hammer and a little wiggle got it in.

[Half-Inch Stud]

Tom, me, et al, You all know what our engine RPM is at 150 MPH huh.

I get giddy when going 75 in the Morning Commute at 2500 RPM. Locking Converter or not.

[Skip Fix]

Originally Posted by Half-Inch Stud

Tom, me, et al, You all know what our engine RPM is at 150 MPH huh.

I get giddy when going 75 in the Morning Commute at 2500 RPM. Locking Converter or not.

Well with the stock 1978 180 HP 400 and stock 2.56 it was all tapped out at 4000. But that was about 130ish with the 265-50-15s. Texas World Speedway College Station TX on the long straight on the oval before you went back down to the road course,

[MidnightAuto]

Thanks for all the great feedback guys. Back tires are 235/60/15 so I could bump up to 70 I suppose. I will call silversport and apt to get a few quotes...thanks guys. Happy thanksgiving.