Rear end ratios

[Pontiacgoodolddays]

Hello All,
I’m looking for gear ratio suggestions, I think to be more specific…the sweet spot. But first, we must qualify the information request with more data! Our subject vehicle is a 1970 Firebird, which will be running a 461 cubic inch (give or take) Poncho. It’s a very popular build and usually folks have great success with it. I’m figuring based on what I’ve read, the engine will come out to about 525 HP and about 575 Ft. lbs. of torque.  The transmission will be a beefy Turbo 400 with a gear venders OD unit hung on the back of it. The rear end will be a Moser 12 bolt “Muscle Pak” using an Eaton TrueTrac differential. The car is pretty much a “Saturday Night Special”. It might get driven 4 times a month in summer, and never in the winter!  So, based on that what do the older wiser gear heads suggest for me? Thanks in advance for the help! - Tom

[firebirdparts]

Would this be .78 to 1?  I am looking at their website.

I would think 3.73 would be pretty nice.  You could do something like 4.11, but I think that's kinda slow for a big Poncho engine.

[737driver]

I’d agree with 3.73 or even a 3.55 . I’d even recommend a 3.23 ratio as well.
Jim

[Wallington]

use the torque, weird to have all these specs and not already worked out that also.

[Pontiacgoodolddays]

Thanks for the replies! Yes, the GV OD is.78 to 1. The torque should come out to about 575 ft lbs. I'm thinking of a 3.42, it seems that would be reasonable. The 461 ought to develop plenty of low end grunt, anyone want to vote against the 3.42? - Tom

[firebirdparts]

I think with the GV 3.42 is going to be 2300 ish on the interestate.  So by modern standards that's still turning pretty fast.  Nice middle of the road number.

[Pontiacgoodolddays]

Yeah, that's bearable...3.42 it is!

[darrylta]

I settled for 3.50 rear gear with a T56 Mag transmission , with 5 & 6 gear  being  overdrives.
The 3.42 diff gear sounds about right.
Hard to beat a stroked Poncho!!
Darryl

[JohnnyBertone]

Currently running factory 3.42s with 29” tires behind my t-10 and 468. Burns the tires all of 1st and 2nd gear but is a rocket ship in 4th when you stomp on it. Was considering moving down to 3.23s or even 3.08s since the motor still had enough power to move and does not need gears to help it