Favorite gear ratio for street car

Favorite gear ratio

  • 4.10

    Votes: 5 13.5%
  • 3.91

    Votes: 14 37.8%
  • 3.73

    Votes: 18 48.6%

  • Total voters
    37
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Wvbuzzmaster

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I have a 1972 Duster with a mild (350-400 hp) 1969 340 with X heads and Purple camshaft. It is mated to a 727 and 8-3/4 Sure Grip with 27” tall rear tires.

Have been chasing driveline vibration and finally located a contributor... chipped tooth on the pinion gear and loose pinion nut... so guess I am rebuilding the rear differential. It is a 489 case with working Sure Grip, and DoctorDiff has all the parts.

Currently a 4.10 but thinking about going to 3.91... any opinions on what everyone likes for a cruising gear for just local driving and some highway driving around 65 mph. Not a race car, but I do like a good launch still. So who has opinions.
 
I have a 1972 Duster with a mild (350-400 hp) 1969 340 with X heads and Purple camshaft. It is mated to a 727 and 8-3/4 Sure Grip with 27” tall rear tires.

Have been chasing driveline vibration and finally located a contributor... chipped tooth on the pinion gear and loose pinion nut... so guess I am rebuilding the rear differential. It is a 489 case with working Sure Grip, and DoctorDiff has all the parts.

Currently a 4.10 but thinking about going to 3.91... any opinions on what everyone likes for a cruising gear for just local driving and some highway driving around 65 mph. Not a race car, but I do like a good launch still. So who has opinions.
Do your homework and figure what you'll be turning at 65. Wallace calculators have a program for that if I remember. If you put a big gear in it, can't hook it up, and are taching 4000+ r's at 55 you have the wrong gear.
 
questions:
  • Do you know what your 60 ft/1/8 mile and 1/4 mile times are now?
  • Does the car hook up good now?
It's all what you can stand to listen to while going down the highway. If there is a lot of highway driving at 65 mph, I'd go with 2.94's. But that's me.
 
My 68 GTS, 340 4 Speed, 284/484, 10.5 cr, headers, LD340 and holley 3310-2 carb, MSD-5C. I ran a 4:30 gear with G70-14 tires.

The car now has stock intake and manifolds, same cam and AVS and I’m going from the stock 3.23 gears to 3.91’s. I feel a 3.91 is the best 340/4speed gear.

Cliff Ramsdell
 
I’ve only owned the car two months and put 25 miles on it. Highway use is low maybe 15% of total driving, but longest highway trip would be about 30 miles. With 4.10s it did good but I the car started with a lot of problems... been chasing the non mechanic repairs out if it. So far I could have started with a better car for what I am spending to save this one. I just installed new Espo 6 leaf +2 springs since the old ones were wrapped badly from not me. So as far as hooking up im good with a nice feeling launch, if that makes sense... i ran the math and 4.10s at 65 is 3300 rpm, 3.91 is 3100 rpm, snd 3.73 is 2900 rpm, not big changes but whatever. I like how the lower gear ratios feel, just wondered if going to 3.91 was smart... not a racecar, but want it to feel like it can run high 11 or low 12 quarter mile, but nice street car manners.
 
My 95 5.2 Dakota has factory installed 3:91s & It cruises well, around 3200rpm at 70-80 mph, but I do have the O.D. 4th gear & that helps a lot. I like the 3:91s for the street. If the motor is built right, you won't have any problems. It will run at 4000 rpm all day long, easy.
 
I love 3.23s as an all-around street/cruising gear, but you're running a somewhat tall tire- I'd look into 3.55/3.73s.
 
My favorite street gears are 4.30's with a T56 and a .63 overdrive 6th gear. 2,200 @ 65 mph.

But realistically, with a standard 1:1 final gear transmission I wouldn't go higher than 3.55's with the freeway driving I do. Even when I was running 3.55's with a 26" tall tire it was a lot. Even with a 4 speed and no converter losses. But the freeways here don't make 65mph easy, I figure my freeway speed at 70mph at least. Nobody does 65 and gets out of the slow lane.

I’ve only owned the car two months and put 25 miles on it. Highway use is low maybe 15% of total driving, but longest highway trip would be about 30 miles. With 4.10s it did good but I the car started with a lot of problems... been chasing the non mechanic repairs out if it. So far I could have started with a better car for what I am spending to save this one. I just installed new Espo 6 leaf +2 springs since the old ones were wrapped badly from not me. So as far as hooking up im good with a nice feeling launch, if that makes sense... i ran the math and 4.10s at 65 is 3300 rpm, 3.91 is 3100 rpm, snd 3.73 is 2900 rpm, not big changes but whatever. I like how the lower gear ratios feel, just wondered if going to 3.91 was smart... not a racecar, but want it to feel like it can run high 11 or low 12 quarter mile, but nice street car manners.

You're not accounting for converter slippage, 65mph @3,300 with your set up is 0 converter loss.

It just depends on the driving you do, if 30 minutes is the farthest you'll ever drive it and that's highway and not freeway you can make the 4.10's work. But you're not gonna wanna drive it for an hour on the freeway anywhere. If you have a freeway commute you'll want higher gears. I ran 2.76 gears in my Challenger forever before switching to 3.23's. It wasn't fast off the line, but I was daily driving it and it worked great. And it would still do a peg leg burnout with it's stock 318 and the hockey puck 245/60/15's that were on it.
 
Like the man said: it's all about what you can put with. I have had,
2:94's, outragous top end! 110 mph in 2nd gear.
3:23,s., very driveable anywhere.
3:55's, better off the line, gas milage gors to SH**. 55-60 mph is about it with out pushing cruising rpm.
3:73, 3:91's, At this point I was off the main highways on secondary roads 45-55 mph.
5:13's, City driving cruise speed about 45-55 at best. but 0-60 mph is amazing.
 
A 4.10gear with a tall tire has the same rpm per mile as a 3.90 gear with a short tire . Likewise a 3.90 gear with a tall tire has about the same rpm per mile as a 3.70 gear with a short tire . Can you see where I'm going with this ? Much easier to change the height of the tire than the ring & pinion to find the sweet spot . If you live in the mountains I suggest a 3.90 gear so you can vary the height of the tire for hills or flats . Good luck , happy 2021
 
The 68 Barracuda in my Avatar has 3.91. Thou in my much younger years I had a 70 340 4 speed Duster with 4.30 gears that I really liked.
 
Ya, I am aware a lot of factors involved in this. Running the 284/484 cam with a 727 automatic. If my 4.10 was ok I would run it but since I have to replace it gives me this opportunity to either stick at 4.10 or go to a 3.91. Not sure 3.73 is aggressive enough for the way I want the car to feel when getting into the throttle but I know the 4.10 does. I also know like 72blunblu stated all my rpm calcs don’t account for converter slip. This is the main reason im considering going to 3.91 given that i may want to run some highway and know thats a couple hundred more rpm higher if accounting for converter slip.
 
Ya, I am aware a lot of factors involved in this. Running the 284/484 cam with a 727 automatic. If my 4.10 was ok I would run it but since I have to replace it gives me this opportunity to either stick at 4.10 or go to a 3.91. Not sure 3.73 is aggressive enough for the way I want the car to feel when getting into the throttle but I know the 4.10 does. I also know like 72blunblu stated all my rpm calcs don’t account for converter slip. This is the main reason im considering going to 3.91 given that i may want to run some highway and know thats a couple hundred more rpm higher if accounting for converter slip.
I think you have answered your own question. You could live with 4.10 (lots cant), and like the idea of 3.91. So, go with 3.91!
I used a roadrunner with factory 4.10s as a daily driver, work commute car for years, and it was tolerable because of a quiet factory exhaust. Most that dont like that much gear, dont like it because of too much noise.
I have 3.91 on a locker in my bracket/street car, cause it was just as quick as with the 4.10 and 4.56 that i used to have in it.
I have 3.50s in a nine in my other car, for potential nitrous use, to avoid running out of rpm at the track. If a car picks up 10 mph or more from nitrous, (very easy to do),too much gear can be really bad.
 
I think you have answered your own question. You could live with 4.10 (lots cant), and like the idea of 3.91. So, go with 3.91!
I used a roadrunner with factory 4.10s as a daily driver, work commute car for years, and it was tolerable because of a quiet factory exhaust. Most that dont like that much gear, dont like it because of too much noise.
I have 3.91 on a locker in my bracket/street car, cause it was just as quick as with the 4.10 and 4.56 that i used to have in it.
I have 3.50s in a nine in my other car, for potential nitrous use, to avoid running out of rpm at the track. If a car picks up 10 mph or more from nitrous, (very easy to do),too much gear can be really bad.
It’s a Mopar with a lopey cam, where else would the magnificent sound come from than the true dual exhaust lol. I guess I am overthinking this again but finding the chipped tooth is not an option but to replace and having not logged a lot of miles like I had expected to see if 4.10 was all I thought it would be in this application, it definitely put me at a disadvantage having the option to stick with door number 1... or switch to door number 2... ahhh, the overthinking.... lol
 
I drive my dart on the street. I drive it about an hour down the highway to the dragstrip. Race all afternoon and drive it back home. I run a 27" tall ET street with 3.73 gears. My combo is a mild 408, 727 trans and a 3300 stall convertor. Its not too bad on the highway but its a noticeable difference from the 3.55's I had. I dont regret it at all.
 
I have to say the 3:91 was my favorite. I also used to drive it to the track, race all day and then drive home. I tell ya humming down the interstate at 6:30 am. was a sweet sound.
 
Depends on the tire height. A car with 4.10's will act much differently with a 25" tire than with a 30" tire.

I prefer tall rear tires. Assuming a 1:1 transmission ratio, 3.91's on a street car with a 28" tire provides a good combo of fun and keeps RPMs tolerable IMO.
 
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