Advice on potential gear swap

-
mmdoctor

mmdoctor

Well-Known Member
Joined
Aug 25, 2010
Messages
57
Reaction score
0
Location
Washington State
Guys, newbie here. Looking for some advice on a potential rear end change. Been running a 3.91-SG last few years (741 case) but end up driving car much more on the highway than originally planned. Considering going to a 2.94 (maybe 2.76) and have a lead on a NOS ring/pinion set. Realize this is quite a dramatic change and just wanna make sure I'm not going to be causing more problems than it's worth (having to change TC, shift linkage, etc) simply making this swap. This is a weekend cruiser only that will never see the track.

Would also consider going to an OD unit (Gear Vendor?) if that's gonna be an easier/safer change but haven't researched this route enough yet.

Thanks all in advance for your help!

276/283 adv, 222/230 at .050, .571/.581, 108 LSA
727 (non-lockup) with 4.2 ratio 2nd gear
9.5" Dynamic TC with 3000 stall
TF-2 shift kit
B&M tranny super cooler
275/60/15 BFG drag radial rear
 
If you only drive casual street and are concerned about gas mileage, then the ratio's you've selected are good. If you are unconcerned about stoplight acceleration, then those ratio's are good. I was there when these cars were new and gear sets were poor. We did many rebuilds. So I would not be in favor of buying any NOS gears. I would buy from Yukon. 3.23 gears are a popular compromise.
 
I have a GV Overdrive and it's been in the car for 20+ years. Once you this route, you'll never go back. I run the interstate with 4.11 gears effortlessly.
 
2.94 gears are my favorite gear sets with the 741 case > for cruising and at today's highway speeds.

Stock '69 318 with added Edelbrock 1406 4 barrel, 727 trans and the 2.94 gears.

Pass anything you want, the light weight Torq Thrust II aluminum wheels helped performance a lot. Less rotating mass to spin up.

Resized_20190721_191121_2357.jpeg



☆☆☆☆☆
 
Definitely think 2.94 is gonna work best for my application now. Again, just want to make sure this swap is going to be as simple as just changing out ring/pinion, new gasket/fluid, etc without having to modify anything else (new TC with different stall, modifying shift linkage, etc).
 
i think the best compromise gear is always 3.23, but i can certainly see the appeal of a 2.94 and i don't think i would personally go to a 2.76 unless i was specifically building a car for long haul road tripping.

given your cam specs, with those long legs it'll change the overall behavior of the ride for sure. while you won't have to mess with anything else (shifter, converter, ect) you'll likely need to adjust your tune to accommodate.
 
I would no go to high of a ratio with that converter. Getting the converter up close to its rpm stall at highway speeds would be good. If not you'll be slipping it to hard and make hydraulic heat.
 
Yes Oldmanmopar, current stall of TC is my biggest concern here. So in your opinion, what's 'too high' of a ratio? I do have a aux tranny cooler and a trans temp gauge to keep an eye on it, but don't wanna be creating more problems than it's worth. Also have seen a 3.08 (harder to find) and 3.23 to consider, but that would be as far as I would go.
 
oh, btw i hadn't caught that you're running a 28" tall tire. with a 2.94~3.23 gear that maths out to 75~85mph speed at 3K

newer converters are built for this type of driving, but i still would keep it in mind in that heat is the enemy of transmissions and all that. and operating something right in the window of "on and off" isn't always the greatest for longevity.
 
What's your cylinder pressure?
To pull 2.94s off the line, yur gonna need a lotta pressure.


I have a similar cam in my 360 and it likes a minimum of 180psi for bottom-end torque and a starter gear of 10>11:1.
IDK what a 4.20 ratio Second gear is except maybe a typo, but no matter,
IMO
2.94s are gonna suck with your combo.
I mean suck at take-off.
By the math, 65 will be around 2380 at zero-slip, maybe 2500 on your tach. So you can tune the ignition for that. So that end is fine.
But take-off is sure to be a lil soft
 
Yes, take-off definitely gonna be soft but not hot rodding/racing at all. Really just going to local car shows but some are a little farther away and require longer/freeway drives.

Few more engine/tranny specs I should have included earlier are listed below.

360 mag - 30 over
370hp @ 5300rpm (estimate, car has not been on dyno yet...plan to dyno soon though)
9.5:1 comp
Upgraded/aluminum planetary gears, servos, and accumulator (front & rear) in 727
 
You must log in or register to reply here.
-

Back
Top