Your favorite rear end/final drive ratio and why?

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MRGTX

MRGTX

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What did you pick? Why? Are you happy? Do you wish that you picked something different?


About four years back, after saving up a wad of cash, I had the chance to pick out my "dream" rear axle assembly. My vision for my car was to make it as fun as possible on curvy back roads, probably take it to the autocross at some point, and to generally make it exciting and engaging to drive. To me, this usually means higher revs and lots of shifting.

With that in mind, I chose a mechanical limited slip (Eaton Truetrac) with 4.10 gear ratio. After living with it with two different engines and two different transmissions (just did a 4spd swap), I am not sure if I would have been better off with a lower numerical (more highway oriented) ratio. The main problem seems to be the lack of an overdrive gear and engines that don't exactly love to rev. The two 5.9s I have had tend make their power down low where they don't need as much help from the short gears.

My current engine is a Blueprint 408 stroker making about 460 at the crank driving an A833 4spd with stock ratios. There's more than enough power to overwhelm the tires in almost any gear...at least with my 255 no-season BFG T/As.

Would it be more fun with 3.23s or 3.55s? I just don't know and experimenting is outside of my budget currently... I'm hoping to learn from you guys before I invest.
 
I am using a 3:55 limited slip. Engine made 415 hp and 435 ft lbs at the crank. I do VERY little highway driving and a lot of backroad cruising around 60 mph. I honestly couldn’t tell you what RPM I am running at 60 but it’s a decent mix. I am considering going to 3:93 if I ever have time or money but it’s not a huge priority.
 
I had a 4.30 back in my Daytona days and I loved that gear. Of course everything was 1/4 mile racing. 8.40’s@160mph. I almost changed out the 4.88’s in my black small block car but I’m real glad I didn’t because every track I run now runs my class 1/8 mile. Ill had from 3.91’s to 5.57’s in my cars. Last full 1/4 mile pass I made in my small block was a [email protected] but that pass was out of snuff around 900 feet. With a 850 carb and a solid lifter cam she was wound tight. Now I have a roller cam and 1000 plus carb so maybe some test n tune I may see if it has a 9.20 something in it.
 
My favorite for mixed driving with a manual trans. has always been the 3.23 SureGrip 8.75. I've got a couple of extra pumpkins with different ratios sitting around (at one time I had it down to about a half hour to switch center sections- but I'm not that limber anymore :)), but I always seem to come back to the 3.23s. Good enough bottom end, and doesn't protest highway speeds.
 
For a street car? With an automatic 4.10’s. With a stick 4.56’s.

Ignore the tach. These engines were never designed to lumber along at 2200 RPM like a late model engine.
 
Professor Fate said:
My favorite for mixed driving with a manual trans. has always been the 3.23 SureGrip 8.75. I've got a couple of extra pumpkins with different ratios sitting around (at one time I had it down to about a half hour to switch center sections- but I'm not that limber anymore :)), but I always seem to come back to the 3.23s. Good enough bottom end, and doesn't protest highway speeds.
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I agree with you there. I have 3.23's in both of mine. They seen to be a good all around gear. I don't have a performance build under the hood so I don't really need anything bigger.
 
Rat Bastid said:
For a street car? With an automatic 4.10’s. With a stick 4.56’s.

Ignore the tach. These engines were never designed to lumber along at 2200 RPM like a late model engine.
Click to expand...


Back in the 1970’s my Dad borrowed my 340 (4 speed) duster and thought it was a three speed. Ain’t got no time for first gear. Lol
 
Without an overdrive a 3.23 is about as much gear as I feel comfortable with in a car that I intend to drive on the highway. Choosing a gear is no different than choosing to large a carburetor, or to large of a camshaft. It can be fun at first but in time you figure out that you went a little overboard.

Tom
 
Daily driver 8.25 limited slip with 3:55 gears.
A bit over stock 5.9 and 42RH overdrive trans.
I do quite a bit of hiway driving and really couldn’t imagine the 3:55 without the OD as the speed limits are 65 and 75 on the main highways.
The 3:55 is great for kicking around town though.
With the OP’s power level and tire preferences I have to agree with the 3.23 suggestions.
 
MRGTX said:
What did you pick? Why? Are you happy? Do you wish that you picked something different?


About four years back, after saving up a wad of cash, I had the chance to pick out my "dream" rear axle assembly. My vision for my car was to make it as fun as possible on curvy back roads, probably take it to the autocross at some point, and to generally make it exciting and engaging to drive. To me, this usually means higher revs and lots of shifting.

With that in mind, I chose a mechanical limited slip (Eaton Truetrac) with 4.10 gear ratio. After living with it with two different engines and two different transmissions (just did a 4spd swap), I am not sure if I would have been better off with a lower numerical (more highway oriented) ratio. The main problem seems to be the lack of an overdrive gear and engines that don't exactly love to rev. The two 5.9s I have had tend make their power down low where they don't need as much help from the short gears.

My current engine is a Blueprint 408 stroker making about 460 at the crank driving an A833 4spd with stock ratios. There's more than enough power to overwhelm the tires in almost any gear...at least with my 255 no-season BFG T/As.

Would it be more fun with 3.23s or 3.55s? I just don't know and experimenting is outside of my budget currently... I'm hoping to learn from you guys before I invest.
Click to expand...
Gear choice is combo dependent not what's popular. Choices are a series of compromises.
 
Daily driver, Shortened Ford 9 inch, 3.70. I don't have to kickdown to pass since Rpms at 55 is at my peak torque.
 
MRGTX said:
What did you pick? Why? Are you happy? Do you wish that you picked something different?


About four years back, after saving up a wad of cash, I had the chance to pick out my "dream" rear axle assembly. My vision for my car was to make it as fun as possible on curvy back roads, probably take it to the autocross at some point, and to generally make it exciting and engaging to drive. To me, this usually means higher revs and lots of shifting.

With that in mind, I chose a mechanical limited slip (Eaton Truetrac) with 4.10 gear ratio. After living with it with two different engines and two different transmissions (just did a 4spd swap), I am not sure if I would have been better off with a lower numerical (more highway oriented) ratio. The main problem seems to be the lack of an overdrive gear and engines that don't exactly love to rev. The two 5.9s I have had tend make their power down low where they don't need as much help from the short gears.

My current engine is a Blueprint 408 stroker making about 460 at the crank driving an A833 4spd with stock ratios. There's more than enough power to overwhelm the tires in almost any gear...at least with my 255 no-season BFG T/As.

Would it be more fun with 3.23s or 3.55s? I just don't know and experimenting is outside of my budget currently... I'm hoping to learn from you guys before I invest.
Click to expand...
I have a similar setup to yours. Was running 3:91"s. Switched to a Dr Diff supplied sure grip with3:55's in a 489 case.

Way more streetable setup with minimal performance loss.
 
I had a 1972 cutlass that I towed with and did a little playing on the street with it. I went from the factory 2.73 to a 3.73 and it didn’t affect gas mileage one bit in hilly Pa. But it sure made a difference in how the car ran. Sure towed good too.

1B989250-168B-4B8C-9E3E-9097B18F2F53.jpeg
 
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Highest possible gear the rear chunk will allow. I have a 2.76 open in the 8-3/4 in my Challenger and a 2.50 in the 9" of my Fairlane. I'm 45 highway minutes from anywhere and like being able to hold the fast lane (75~80mph)without sounding like a NASCAR event at 4k rpm.
 
Ford 9 inch will handle that power and torque. 8 3/4 needs alot of beefing up with sticky tires at that level. A 9 1/4 Chrysler will be too heavy and affect handling.
 
Current combination is a 360/727 in a 75 Dart Sport with 4.10s in an 8.25 sure grip. Way too much gear for what I want or need at this point. I like to drive my car, city and highway, not just 1/8 mile at a time. The gears will be changed in the near future, once I can afford to.
My 70 Dart ran a 360/727 also, but with 3.23s in an 8.75 with a tru-trac, good combination for me and what I need, did a lot of driving and the occasional trip down the 1/4 mile.
I might go to a 2.94 when I swap out the ones in the 75, since I don't plan on doing any racing, just using it for a daily driver.
 
In my 73 Duster 470 auto 391s, 68 Roadrunner went from a 323 SG to a 276 to keep up with normal traffic @ 90 mph. My 67 Chevelle wagon 373s with a TKO for the same reason. 73 VW Thing slug bug 50 hp barn burner= never mind.
 
In my 408 4spd 67 Belvedere I like the 3:23 sure grip. My 65 Dart 273 8.75 3:23 open. For my 69 Dart will have a T56, rear gears undecided. Dustin
 
for a mopar, i choose 3.54 for dana or 3.55 for 8 3/4. for my 69 z28,302, i choose 4.88 or 5.38 for street. with wife driving back and forth to work(7 miles for her).
 
I just love 4.10's for spirited street driving. Long distance highway 3.23's are a good comprised. Put a 3.54 in my 500 inch charger but I'm going back to a 4.10. My 69 340 Cuda 4.10's. I've just been a fan of 3.23's and 4.10's for street driving. And don't use anything smaller than a 27" tire, 28's work find if you've got some hp.
 
I had 2.94s in my Duster (8 3/4) for years behind a ~450hp 360 and 904 with a cheap loose 2600-rpm stall converter. It was really nice for cruising on the freeway at 75-80 mph but off the line was kind of soggy. Last fall I finally put in 3.55s with fresh sure-grip and it's a much better match with the engine's torque curve. I need to put the 2.94 ring gear on to the spare open diff I have and install that back into my 741 case so I can swap that 3rd-member in if I want to go on a longer highway cruise but for going 65-75 mph the 3.55s aren't bad at all, turns around 3400 rpm which I can take for about 30-45 minutes, maybe an hour max but this car isn't as street-friendly as it used to be.

3.23 or 3.55 gets my vote for best all-around highway-friendly ratios, if your tires are in the 27-28" diameter range. I tried 4.10s once and they sucked on the freeway, 4k rpm was too much for me to handle I was stuck going 55 mph and getting passed by everyone. Engine ran hotter too spinning that fast, at that time I had a milder 360 that ran out of breath at 5k rpm.

I'd personally only bother with 3.9x-4.xx ratios on a more drag-oriented car with an engine that made power well past 6k rpm, and/or with overdrive.
 
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