Rear gear change and drivability.

[EFI-Cuda]

I am looking for input and advice on a rear gear change and it's effects on daily drivibility.  

I currently have a Cuda with 3.23 rear gears, an A-518 automatic (the 727 with overdrive) and a mildly modified 360.   The car feel heavy and a bit sluggish while doing normal light to light part throttle street driving.   After all,  the Cuda does weight 3600 pounds.    I know that going with 3.91's or 3.55's will make the car feel better from light to light, but at what cost to highway rpm's and gas mileage?    

If any readers have changed from lower to higher numerical gears, I would like your input of how your mileage and daily driving was affected by the change.   Often, the discussion about a rear gear change centers around performance and quarter mile times instead of daily drivability, highway rpm's and gas mileage.

I appreciate your comments and input.

[Rev-It-Up]

Look forward to the responses on this one.  We also have 3.23 gears and a 727.  We're not going to race it, just street driving.  Wasn't planning on changing it out, but be interested in the answer.

[EFI-Cuda]

By the way, back many years ago when I was in college, I had a Dodge Challenger with a 318 and a 2 bbl.     I changed to a 4 bbl holley and switched the rear gears from whatever was in the stock rear end that I broke to 3.91's and the car just flew.  I remember that the car became an animal with the rear end change.    Now, back then I was a young college student, I was only concerned with speed, so I made no observarions whatsoever regarding daily drivability or gas mileage, and besides, I had no idea what gears were in the Challenger's rear end to begin with.    So I don't doubt that there will be a performance gain from changing gears.

Since I have now touched on topic of performance,  does anyone have any documented quarter mile time differences that resulted from a rear gear change?

[MEK-Dangerfield]

The big question here is just what do you want to do with your car? If you are doing any racing, then that 3:23 is no good. I have that in my car and I just love it. I have a 440, but I just cruise the highway on nice sunny days. Don't go above 3:55 if you are like me. If you go to a 3:91, or 4:11, the engine would be screaming at highway speeds. Probably pushing 5000 RPM's. That won't help gas milage . Anyway, the higher gear ratios will help performance, but I don't think that is the way to go for a car you aren't racing. That's just my opinion.

 1974 Cuda360,
   Have you ruled out other problems for the sluggishness? Like a bad carburetor?

  Mike

[Carlwalski]

Sounds like you get out enough not to install 4:10's, plus the highway can kill you with gears like that LOL.

I have 3:55's and a TF-727 it's the best combo, the best of both worlds, quick around town and deadly on the highway. Highway rpm's are around 2-2,500 no vibrations and it really wants to dance on the Highway but I can't afford the tckets as of now.

I'm not changing my 3:55's, if I did 3:91's would be OK, but I drive heaps so I want it just right  

[DodgeFreak]

I haven't had these gears but from what i read and what i know........if your looking for quick light to light but good gasmilage on the highway go 3:55..i think they would be the best all around 3:92s wouldn't hurt either since you have the OD in the trans.  4:10s would be pushing it i think...

[moparbowhunter]

the O/D trans will help you out on the hiway if you go to a deeper gear. but it depends mostly on what you are gonna do with the car. just cruise or lots of hiway driving or just playing in town light to light. i would assume that because you have the O/D you do take some trips on the hiway. i thikn id go with the 3.55 if that is the case. you will still ahve some decent power at the low end but you can still go out on the open road and not run your motor to death, which the O/D will help you out a lot. i dont knwo any specs for milage and rpm's with your setup. IMO i would hit it with the 3.55 so you have the best of both worlds. if you wanna hit the strip quite a bit and still hit the open road id go with the 3.91 cuz you will have the good launch but that will hurt your milage on the hiway.  i hope this helps.  

[DodgeFreak]

Now that i think of it.............if the gear ratio in the 518 as it is in my dads truck at 60 with the od off and 3:55 gears its around 3grand........SOOOO 3:91 gears wouldn't be to bad...i am thinking more 3:91 because with the OD you will be around 2 grand alittle more which isn't bad.......enless i am figuring things wrong... :-\which i probably am...just my other .02 worth of useless knowledge.

[Chryco Psycho]

Does anyone know the exact ratio of the 518 od  gear so we can give some real rpm scenarios ?
if the od gear is around .7 you have the equivalent of a 2.73 rear gear in od on the highway using the 3.91 rear

[EFI-Cuda]

I did some checking and found that the gear ratios on the A-518 transmission are:

A-518         2.45,  1.45,  1.00,  0.69

So if I changed from 3.23 rear gears to 3.91 rear gears, how much difference would this change make on the highway?      How would my cruising rpms change?    

I am already certain that the vehicle's performance would noticably improve with such a gear swap.     I am trying to assess the impact of such a change on daily drivability, gas mileage and highway rpms.

By the way, thank you all for your responses.    I value your input.

[keith]

i would advise you not to go to 3.91 in your rear. stick with 3.23 or go to .55's. your highway travel will suck with .91's.

i have 3.91's and i love them in town but i can't drive my challenger very far on this gear. i don't like putting that kind of wear on the engine, transmission or the gears for long periods of time. i'm actually planning on grabbing some 3.23 or .55's for a change.

imo your money would be better spent on a posi unit swap.

[moparbowhunter]

what tranny are you using keith?

[DodgeFreak]

according to his sig its the 727 which would be why his engine is screaming with 3:91s...but 1974cuda has the 518 which has the OD...enless keith switched trans ...

[Chryco Psycho]

the 3.91 will be perfect with the .69 ratio over drive , you could even use 4.30, with the od you would have the equivalent of 3.01 rear gears in OD

[Carlwalski]

  Man that sounds good!!! Can you buy an aftermarket Over Drive kit for a 727?? Like 4 gears pretty much?