Gear choice

-
remytherat

remytherat

Well-Known Member
Joined
Jun 1, 2023
Messages
500
Reaction score
557
Location
Los Angeles
'69 dart
mild 360 magnum: 9:1, cam is 214/221, airgap and 650 eddy
26" rear tire
mix of city and highway driving

I have two rear ends to choose between, both 8.25: 3.21SG and 3.55SG.

On fence about what to pick.

Opinions?
 
The 3.55 are gonna rev more on the highway, if that's acceptable to you then run them if not run the others.
 
you want a hot rod, go for the 3.55's baby!

besides gas will be $0.99 a gallon here in no time!
[tongue planted firmly in cheek]
 
junkyardhero said:
you want a hot rod, go for the 3.55's baby!

besides gas will be $0.99 a gallon here in no time!
[tongue planted firmly in cheek]
Click to expand...
I think you mean $6.99.
I would choose 3.21 (3.23) We don't seem to have as much tolerance for high rpm in this age of o.d. trans.
On the other hand..... with 3.55s and a tall tire, it can act similar to a 3.21, but you can put short tires on it and get more performance than the 3.21s
 
Tough call, I can understand your dilemma... neither one is a bad gear for your intended use.
My guess is to take a long, realistic look at how much highway vs city driving you're actually going to be doing, and base your decision on that.
I honestly think stop and go LA city traffic isn't going to allow for much stoplight fun anyways, and you'll be happier when you get out on the open highway (is there such a thing anymore? Last time I was on an LA highway I spent four hours at an average of 5 mph between Anaheim and Long Beach...). Best bet is to make sure it cools well at idle and has a good radio. :)
 
Because the Dart is a light car [ relative to other models ], I would pick the 3.21
 
3.21 for sure. If you are indeed swapping to an AX-15 you'll want a taller rear end ratio as the 1st gear is very deep, iirc 3.6x:1 and 5th is not a very tall OD ratio at 0.79:1. @75slant6 has one in his Duster and I think he put 2.94s in his car to make 1st hear not useless.
 
I'd go with the 3.21. You can still get decent performance with those gears, and they will be much nicer on the highway. If you are more concerned about acceleration and burnouts, go with the 3.55s.
 
Like @MopaR&D said, if you are installing an ax-15, you definitely don’t want anything lower than a 3.21. I originally had 3.23’s in my Duster with 25.6” tires and first gear was basically useless aside from taking off on a hill. I’ve switched to 2.76’s and it’s MUCH better. In fact, not accounting for torque multiplication from a torque converter, the ax-15/2.76 combo is almost identical in rpm/mph as a 904 with 4.10’s.
 
I'd love to try 2.76 in my Ragtop. We drive 80 MPH here in NE. Seems to be the norm now even though speed limit is 65. I'm no longer a hellion street driving and drive pretty mellow now so I could sacrifice street performance for long highway cruises.
 
Last edited:
remytherat said:
'69 dart
mild 360 magnum: 9:1, cam is 214/221, airgap and 650 eddy
26" rear tire
mix of city and highway driving

I have two rear ends to choose between, both 8.25: 3.21SG and 3.55SG.

On fence about what to pick.

Opinions?
Click to expand...

i'm running a 3.23 with a 225/60-15 and want to go to a 2.76 or gear vendors but thats expensive. the 3.23 runs about 3k at 70 mph. i have a low gearst 904 and a good converter so i'm not worried about it not being peppy still. plus like @Kendog 170 said i basically putt putt around town so i don't need anything more gear.. i'm more focused on road trips these days..
 
MidnightSwinger said:
Smiles per gallon not miles per gallon. The difference between 3.21 and 3.55 won’t break the bank, I’d wager.
Click to expand...

after our recent road trip i can say the car was much more comfortable cruising at 70mph which was about 3000 rpm then it was at 75 - 80mph which was 3400+ rpm. it was even more comfortable at 60-65 mph whid was like 2500-2700 rpm.

it all depends what the intended purpose is i guess. if you are mostly aroud town then hell go 4:10. but if you actually use the car for road trips and frequent the highway then i'd prefer something more in the 2.76 area.
 
abodyjoe said:
after our recent road trip i can say the car was much more comfortable cruising at 70mph which was about 3000 rpm then it was at 75 - 80mph which was 3400+ rpm. it was even more comfortable at 60-65 mph whid was like 2500-2700 rpm.

it all depends what the intended purpose is i guess. if you are mostly aroud town then hell go 4:10. but if you actually use the car for road trips and frequent the highway then i'd prefer something more in the 2.76 area.
Click to expand...
The car was more comfortable or you were more comfortable? It’s absolutely a personal choice thing, I’ve got no problem driving any vehicle in the middle of its rev range.

I have driven 4 cyl commuter cars daily that spin 3,000+ rpm at highway speeds. Motorcycles that rev higher than that at highway speeds and drove trucks professionally that routinely would spin 3500 on the highway due to load weight and terrain.If you have a loud/droning exhaust then I get it. Otherwise rev that puppy.
 
MidnightSwinger said:
The car was more comfortable or you were more comfortable? It’s absolutely a personal choice thing, I’ve got no problem driving any vehicle in the middle of its rev range.
Click to expand...

car was more comfortable.. you could hear it.. sounded much better at 65is then at 80. gas gauge went down much slower at 65 then at 80 too.. :). my exhaust is quiet as hell at just over 50mph up to 100mph. atleast inside the car.
 
abodyjoe said:
car was more comfortable.. you could hear it.. sounded much better at 65is then at 80. gas gauge went down much slower at 65 then at 80 too.. :). my exhaust is quiet as hell at just over 50mph up to 100mph. atleast inside the car.
Click to expand...
How did it sound better?
 
You must log in or register to reply here.
-

Back
Top