I'm running a 3.55 in my '69 Charger with a 440, 727, 3000-3200 stall, and 295/50/15 BFG's.

@ 70 mph it's around 3200 rpm, on the back roads which are 45 mph zones it's under 2500 rpm.

I don't mind driving it on the interstate, but it does get annoying. Farthest trip I've taken was about 35 miles (70miles RT) and that's enough for me.

But the way I see it, it's not a daily driver for me anyway, just a fun car. I don't have to drive it 100 miles one way and as little cruising as I do in town, the 3.55's are suffcient.

I have an '89 Diplomat AHB that has 2.94's and it is much more relaxing to drive it on the interstate. Around town though the car really isn't the dog you think it would be, but, it has the A999 in it which I think may have a lower first gear.

If I did build another car to do it all with, I would consider the 518 swap if I had an automatic, or saving up and spending the dough for the Keisler if I had a manual.

29 inch tiers and a comp cam extreme energy 230/477

I'm on 3.55 with 255/60R15. I had 3.23 on same wheels. Got plenty happy and variation is not that BIGGER to get worried.

Both of them works for cruise, then mileage is what you will need to think. Myself I don't care the 10% mileage change ( Ok I pay US$ 3 to fill my tank on a 74 Charger, so who cares milage LOL ). I mean 10% cause that's more less the gear variation.

overall, 3.23 is the best gear setup for highway to win torque from 2s gears. For street, both works great really. If you are going down from 4s, I think 3.55 is the best to keep some of the high gears you had and FEELS you are not loosing a lot.

I went from 3.23 to 3.91's with 28" tall tires in the Duster and it was like night and day. LOVE it. I do a lot of freeway driving too, and it doesn't bother me a bit. Maybe my tolerance is higher than most, lol.

I also have an efficient PTC converter, which lowered my RPM by a couple hundred compared to the stock converter.

Keisler Tremec TKO, 3:54, 14's. Sweet-spot cruising all day long.

I'm running a 28" tall tire with 4.10 gears behind an A500 overdrive trans. Runs a tick under 2500 RPM at 70. OD was one of the best modifications I made to my car.

I have a 2.26 ration in overdrive.(3.23 axle) Very relaxed cruising at 70 MPH, about 1900 RPM and good gas mileage.

I'm running a 518od and 3.91 gears with a 28" tire at 2200rpm at 70.

Well . . it certainly all depends what you use your car for . . . in my 74 Duster360 (stock), before going to Carlisle years ago, I swapped out the 8.25" rear end (complete) that had 3.55:1 gears, for another that was 2.45:1 gears !!! Yes, that high . . . with the 360, 727auto, 235/60/14 tires, cruising 70mph = 2500rpm !

With the torquey 360, it has no problem spinning the right rear (yeah a one legger), and love the passing power on the highway !!! Not to mention getting 22mpg @ 70mph !!!!

As I have always said, you have to build the car for you . . .for what you want to do. I like driving LONG distances to car shows, not being a drag racer or street fighter. So the car works for me !! Course I miss my big ole C Body for long distance cruising . . . .

Just my

Cheer

Mark
A12rag

Stumpy, is yours a 3 wire?

I had 3.23 to 4.30 in my purple car over the years. At first you think you are going to drive it a lot,but now if I put 500 miles a year on it its a lot. I ended up putting a 4.10 Dana in it and love it. My blue car has 3.55 in it,but I drive it more,about 2000 miles a year. If I ever get the 70 done it going to have a 3.54 Dana in it.Because thats what I have for it. If you are going to drive a lot,2500 miles or more then go with 3.23,but I bet you will end up changing to 4.10 because these old car do alot of sitting and 4.10 are a lot of fun on the street. Just my

Yes it is. The switches I used give me a lock up at 50 and od at 55. I also have an on-off switch hooked up to the vacuum switch that kills both.

With the tourque of a True 10:1 + 440 c.i. or bigger ~28" tire the 3.23s are a very good choice.You can still get it out on the interstate. And roast the tires around town at will. And no overdrive needed for 140+ top end!

With an A-518 doesn't it downshift out of overdrive when vacuum goes to zero ? If so how do you go 'full-throttle' while in overdrive ?? Will the transmission even go into overdrive while under full throttle ?

If you stomp the gas it will come out of OD but if you ease into it no problem.