Rear end gear with 727?

[Moparkrazed]

Hey guys, still thinking out my 71 charger build. I’m still between a 440 and 6.4 but my question is if I go with a 727 would I be able to run 80mph without killing the motor with rpm’s. I think the car has 200 something rear end in it now. Would a 727 be ok or should I swap out to a 4 or 5 speed?

 

[RemCharger]

2.76 gear works well for that.

 

[Moparkrazed]

2.76 gear works well for that.

awesome. That is what I was hoping but didn’t know for sure. What would you guess would be the highest to go? Low 300, probably nothing higher than that? Thanks again.

 

[RemCharger]

3.23.
Oh, and a 4 speed has the same final drive ratio as a 727. 1:1

 

[Moparkrazed]

Awesome. Thanks for the info! I’m still pretty far out on getting engine and trans but still want to have a direction and also learn more as I go. I appreciate your replies.

 

[ruffcut]

Many drag racers use a 727 transmission with 4.56 and steeper gears with no problems. Of course they are usually beefed up for racing, but still retain the same gear ratios as a stock 727. On a side note, my max wedge clone runs a 727 and has seen mph in the mid 130's. ruffcut

 

[R/T Boy 67]

Decide on rear tire size, find out for sure what ratio you have, and do the math.

 

[Moparkrazed]

Many drag racers use a 727 transmission with 4.56 and steeper gears with no problems. Of course they are usually beefed up for racing, but still retain the same gear ratios as a stock 727. On a side note, my max wedge clone runs a 727 and has seen mph in the mid 130's. ruffcut

I know the 727s are pretty stout transmissions. I’ve never owned one, just have my 904 in the dart and A 903 ( I think ) in my 66 valiant. But the charger I plan on using a lot more and want to do a lot of road trips. So looking for something that has top end without killing the motor with high sustained rpm’s.

 

[Fran Blacker]

If you run 3.23s with 26" tires I'd say 3200/3300 rpm. How big a tire do you need to get it under 3000rpm. Ran 3.54s with 26" tire 3000rpm at 70 mph.

 

[Moparkrazed]

If you run 3.23s with 26" tires I'd say 3200/3300 rpm. How big a tire do you need to get it under 3000rpm. Ran 3.54s with 26" tire 3000rpm at 70 mph.

Not sure on what size I’m going yet but definitely appreciate you letting know what rpm you are turning with ur tires and gear ratio. Definitely helps me out. Thanks for posting that.

 

[Black_Sheep]

Decide on rear tire size, find out for sure what ratio you have, and do the math.

This, there are all kinds of tire size/gear ratio/RPM calculators online…

 

[Thrashingcows]

I've run both 2.76 and 3.23 in my 68 T/C wagon, 440/727, and 225/70/15 tires, and while the hwy cruising with the 2.76's is a little better the in town and low end pick up is kind of poor, and having the transmission constantly jumping between gears from part throttle kick down pressure being low due to lower RPM's is really annoying. I prefer the 3.23's much nicer all around cruising and Hwy gear and the whole car seems to perform better.

 

[Cranky]

904's and 727's.....and no 903's. Ran a 2.94 behind a 383 and it did good on the highway with 27" tires and wasn't bad in town being a small big block. A 4.56 behind a 340 with 29's was fun in town with a 71 Cuda. Pick your poison. I like deep gears with an OD trans....

 

[Lefty71]

904's and 727's.....and no 903's.

 

[Gus chiggins]

3.23.
Oh, and a 4 speed has the same final drive ratio as a 727. 1:1

Hate to sound like a noob, but what stall torque converter?

 

[fourgearsavoy]

I'd go with 4-speed and 3.23's with a 28" tire. Chargers look good with a larger tire to fill the well.

 

[Moparkrazed]

I'd go with 4-speed and 3.23's with a 28" tire. Chargers look good with a larger tire to fill the well.

I do like that look.

 

[SlinktRR]

I use 3.23 and 3.55 with 499ci and 28" tire. I like the 3.23 most of the time, around 3000rpm at 80mph which is fine with good mufflers that don't drone. I enjoy freeway blasts with 3.23's, definitely no 2.94 or 2.76.

 

[Moparkrazed]

I use 3.23 and 3.55 with 499ci and 28" tire. I like the 3.23 most of the time, around 3000rpm at 80mph which is fine with good mufflers that don't drone. I enjoy freeway blasts with 3.23's, definitely no 2.94 or 2.76.

Thanks for the feedback on it. I’m leaning 440 around 530 or so hp. I do want some fun around town but don’t want to be scared to jump on the interstate to travel a few states as well.

 

[SlinktRR]

With 500hp you will enjoy the 3.23, can keep up with modern traffic pretty effortlessly. 2.76 is just too tall for even a stout motor.