[DKS]

I want to change my 1970 GTO gearing from 3.55 to 2.93 to get the rpm’s down for better cruising. 8.2 10 bolt. I found an Auburn posi carrier that will accept 2.93, 3.08 and 3.36 gears but can’t find the 2.93. Ideas anyone??? I think I might have to settle for 3.08.

[george kujanski]

The 293 is 82% of your 3.55 whereas the 3.08 is 82% .
Assuming starting at 3000 RPM, the 3.08 will probably give you 2580 RPM and a 2.93 will result in 2460 RPM.. not much of a diff.

Go with the 3.08, it seems to be available with Auburn

George

[rohrt]

When I was messing with RPM calculators for a better crusing in my bird I thought the 2:93 gear was the most ideal. However I already had 3:08 gears to use and went with them vs the 3:36 I was running at the time. I can tell I lost some torq off the line but man I really love the way I can cruise now.

[DKS]

Thanks for the input guys. I think I’ll go the Auburn posi and the 3.08 gears.

[grivera]

I cruised 3.08s in my bird for years - really a great all around gear for a non-OD trans

[DKS]

Glad to hear it Grivera. Another endorsement for the 3.08’s. After that I’ve got to get the trans back closer to stock. The previous owner put in a really hard shift kit and 2800 stall converter. Maybe good for the drag strip but super rough around town.

[Gary H]

Who makes a 3:08 for 8.2" BOP? I don't know of anyone.

[track73]

I had a 2.73 from a Camaro and put it in my Transam. The 455 has so much low end torque that you don't really notice it in town with my 4 speed.

[DKS]

Originally Posted by Gary H

Who makes a 3:08 for 8.2" BOP? I don't know of anyone.

Gary H, I don’t know if I would trust Rigid Axle but here’s one if my photo attaches…

[Tandyman]

DKS, I believe you need a BOP 8.2 gearset. Rigid (and pretty well everyone else) lists separate BOP 8.2 gears sets with 3.36 being the minimum .
Glenn

[DKS]

You’re right, I didn’t notice that. Thx

I did find someone who has a 2.93 gear set in their attic from a change long ago. Says they’re in great shape. Maybe I’ll try those with the Auburn carrier that will accept them.

[Skip Fix]

College buddy swapped a 2.56(I think) wagon rear in his '64 GTO so gas mileage was better commuting the 300 miles. Rode in it it would almost idle at 30 mph!

[DKS]

I hope I’m not going too low with 2.93. If I can get them. I just know that the 3.36 would not be enough of a difference from the 3.55’s I have now.

[locomotivebreath]

You mentioned cruising rpm’s , do you mean highway speeds ? Is this a stock engine ? I realize rpm tolerance is a personal threshold but 2.93s seem really tall . I run 3.90s & 4spd with 28 inch tall tires and I don’t think that I would enjoy the car with anything less . This is a mild 406 that I just cruise , not race . 90 percent of my driving is 60mph or less though . The 28 inch tall tires tame the gears up . I run them because I like the way that they fill out the wheel wells on an A BODY , not to reduce the rpm but it’s worth thinking about as an option and easier . I like the RPM calculator on Randy’s ring & pinion sight , play around with different gears & tire heights and see what ya think .

[geeteeohguy]

Your 3.55 carrier will only accept a gear as low as a 3.36. For the 2.93-3.08-3.23 you will need a different carrier. I had the 3.55's changed to 3.36 in my '65 GTO 4 speed car 34 years ago and it made a noticeable difference on the street. Highway cruise speed went from 60 mph to 70 mph at about 2800 RPM. I swapped the entire 3.36 open rear out of my '67 GTO with a TH400 for a free 2.56 limited slip unit (the whole axle assembly) about 15 years ago and love it for an automatic cruiser. The car cruises 80 mph at under 2500 rpm and returns 21mpg at that speed. Also runs cool and quiet. IMO, for an automatic GTO, a 2.93 is about the perfect compromise ratio. For a stick car, I like a 3.23 or 3.08. I drive distances, and don't like being wound up tight in the slow lane.

[Radman]

I have a 3:50 Ford 9 inch, behind a 700R4, and a 389 in one of my Tempests. 4th gear is a .7 overdrive in that transmission. .7 times the 3.50 equals a 2.45 ratio. 27 inch rear tires. 70 MPH is 2000 RPM. 55MPH is 1400 RPM.

[Half-Inch Stud]

We had a 70 400 GTO with the 2.54:1 POSI. Really fun thru 2nd and highway. 1900 rpm at highway speed was the best. MPG was 20 or so.