Differential Gear Ratio Question

[RCE1962]

Q1. What gear ratio tends to be the "favorite" here for cars with the 409.

I understand that these preferences change depending on various engine builds, torque and max RPM, as well as, "Automatics and Standards".

Currently, the car is just driven a few times on weekends in the summer and will eventually be taken to the local strip every once in awhile....so higher "numeric" gears are OK with me. Would prefer good launch versus highway gears and MPG based on limited use.

Q2. Will stock rear-end be OK or should I consider some of the aftermarket parts for this?

The transmission is not orginal to the car. : A tranny shop here has decifered the 4-speed, that the previoius owner installed, and it is a Close-Ratio Borg Warner T-10 built in 1978. VIN stamp is 28N139114. The first digit represents Pontiac and the second digit 1978 the third figure "N" represents "Norwood Ohio as a Plant Code" They will get back to me about 1st gear but probably 2.43.


Thanks

Ron

 

[chevykid]

Q1. What gear ratio tends to be the "favorite" here for cars with the 409.

I understand that these preferences change depending on various engine builds, torque and max RPM, as well as, "Automatics and Standards".

Currently, the car is just driven a few times on weekends in the summer and will eventually be taken to the local strip every once in awhile....so higher "numeric" gears are OK with me. Would prefer good launch versus highway gears and MPG based on limited use.

Q2. Will stock rear-end be OK or should I consider some of the aftermarket parts for this?

The transmission is not orginal to the car. : A tranny shop here has decifered the 4-speed, that the previoius owner installed, and it is a Close-Ratio Borg Warner T-10 built in 1978. VIN stamp is 28N139114. The first digit represents Pontiac and the second digit 1978 the third figure "N" represents "Norwood Ohio as a Plant Code" They will get back to me about 1st gear but probably 2.43.


Thanks

Ron

Sounds like your trans is out of a Trans Am thats what Pontiac used in the Bird in the mid 70's. I really like a 3:55 behind a 409 and a 4-speed.

 

[jim_ss409]

3.55's are a pretty good all around ratio. 4.11's would be perfect around town but when you hit the highway it feels like you're driving in second gear. If you go the other way, like 3.08's it will be fine on the highway but it will be sluggish off the line. Wide ratio transmissions have a lower first gear so they work better with "highway" gears like 3.08's but with a close ratio transmission lower gears like 3.55, 3.73, 4.11 or 4.56's work better. A 2.43 first gear is fairly low, for a close ratio transmission, and your cam's not too wild so you might be able to get away with a 3.36 or a 3.08 rear end but I think 3.55's or 3.73's would probably be the best compromise.
The rear end will probably be fine as long as you don't abuse it too much.

 

[Impalaguru]

I had a 3:08 in my car for a brief period of time (only becasue it was a junk center section) and I felt very little difference comming off the line as compared to my 3:36. I only gained about 225 rpm on the highway. I have a pretty short tire (215 70 14). I plan to put a taller tire on the car. The 3:36 is a nice gear, though.
Ross

 

[RCE1962]

Thanks for the info so far guys.

So that's two opinions that agree about the 3:55's..... with one opinon regarding a "maybe" regarding 3:73's and no more than 4:11's.

Anyone else running similar or different?


RCE1962

 

[RCE1962]

The range now widens to 3:36 gears as a preference.


So...3:36 to 3:73 is now the "normalized" range so far. The overall range of gears presented reflect a low of 3:08's to a high of 4:11's


Can these gears beat the gearing in typical pony cars? All else being reasonably equal?

Ron

 

[Ronnie Russell]

Ron, I would vote for the 3.55 as the best all purpose gear, however, since you say you only drive a few weekends during the summer, I would pick the 3.70........... .

 

[Tom Kochtanek]

Good advise!

Ron, I am running a 3.36 posi in my '62 and I bet you would be happy with higher numeric gears, although these perform just fine for me (now).

I am using the stock wheels with 14" radials and the engine is a bit aggressive, being a solid lifter stroker with a CPG-selected pistons and camshaft . I can literally rip the rear skins off if I wanted to (tires are the weak link in my drive train), but she drives well around town, and is very smooth on the freeway. Won't win any trophies coming out of the hole, and probably not as aggressive in street driving (beating those Mustangs!), so the suggestions that gear from 3.55 to 3.70 (and perhaps up) seem best suited for you.

The next one will likely have 4.88s in the rear, but that's another story...

Cheers,
TomK

 

[models916]

fours

I run a 4:11 posi on my t400. 2400 stall, stroker 385. Seems just right around town. I tried to use the 4:88 that was in the car from the SBC, but seemed to waste the huge torque that the W was making. Anything less than 3:70 and the Stangs will blow by you real quick or you go up in smoke.

 

[MRHP]

I am running 4.11 in my 62. 27 inch tire and a t 10. I can run 60-65 without a problem, but rpm is 3000-3200. A little high but I like the acceleration. Still can run 120-130 mph for short periods. Like when passing two vettes and a 440 6 pack challenger! I get out of the throttle in high gear around 6500.

 

[MRHP]

Gears

Little update. Last year with 3.36 gears I was getting 13 mpg. Now woth the 4.11 gears I am getting 9. I thought it would be worse! If you were not going to the drag strip, 3.55 or 3.70 would be a nice street gear. I have yet to make it to the track. I still like my 4.11 gears but the speed limit around here is 55. No freeway briving. If I had freeway driving the 3.55 or 3.70 wound be manditory. Hope this helps! Brian

 

[dq409]

Ron, I would vote for the 3.55 as the best all purpose gear, however, since you say you only drive a few weekends during the summer, I would pick the 3.70........... .

I thought that it was common knowledge that the 3:70 gears were weak.

If you only drive a few weeks and want to run with the "stangs" I wouldn`t use any gear higher then a 4:11 !!!,,dq

 

[Ronnie Russell]

dq, I have never used a 3.70, but intend to in my current car. Is there a problem? If so, can you give more details? Thanks.........

 

[Dond409]

I have also heard that the 3.70's were weak. As in easy to break. I had 3.55's in the wagon. They are a good street gear. I went 12.76 with them @ 108.

 

[dq409]

dq, I have never used a 3.70, but intend to in my current car. Is there a problem? If so, can you give more details? Thanks.........

I think it was Aubrey that commented on them several times.
Something about the ring gear detraction and breaking,,, OZ?????

 

[CDNpontiac409guy]

Been my experience, DQ .
I don't know if it's the pitch on hte teeth, or what... but they don't take NUTHIN':eek: !!!

3 sets... even a small block... sheered teeth off, and broke nothing else.
3.08's seem to have a similar "condition".

3.55's, for me, have always been industructable.

 

[models916]

No probs

Not going to have ring and pinion problems if you use Richmond Gear.

 

[RCE1962]

Gentlemen....this is exactly the information I was looking for. Thank you.

Ron