Opinion on rear end ratio choice
 

Hey guys, looking for an opinion on selecting a rear gear ratio. I have a Ford 9 inch with a Dodge Viper T-56 in my 67 Firebird. The motor is a stroked Pontiac (461) with Edelbrock heads.

Transmission ratios in my T-56 should be:
2.66; 1.78; 1.30; 1.0; .74; .50

I'll be using a 285/40/18 rear tire, so about 27"

I ran 4.11 through an online calculator and got the following:



mph/rpm 1000 2000 3000 4000 5000 6000
1st 7.3 14.7 22 29.4 36.7 44
2nd 11 21.9 32.9 43.9 54.9 65.8
3rd 15 30 45.1 60.1 75.1 90.1
4th 19.5 39.1 58.6 78.1 97.6 117.2
5th 26.4 52.8 79.2 105.5 131.9 158.3
6th 39.1 78.1 117.2 156.2 195.3 234.3


What do you guys think? Go with the 4.11 final ratio?

Let me try that chart again so it's easier to read:

I don't really like a 4.11 with that torquey stroked engine and the gear spread between 1st and 2nd in your trans. 1st will be useless and 2nd is a big drop from 1st.

I wouldn't worry about the 2nd overdrive. One overdrive is enough. You have a tall tire compared to many as well.

I'd say something in the high 3's if it were me... a 3.70 or 3.89.

3.89 is the other option I was considering. Thanks for the input, all the "on paper" stuff looks good but it's the actual experience that I'm looking for and appreciate in helping me decide. Here is the same chart, except with a 3.89, will the 3.89 make 6th completely unuseable? I would like to maximize the benefit of all the gears, otherwise why go through the trouble of getting this transmission to fit?

I will whole heartedly disagree with 4.10 not being a good choice with a 27" tire.

I run 4.56's behind my t56 and 406sbc. with a 28" tire it was PERFECT. now that I have went to a 335/30/18 that is only 26" tall, it still works well. although, a 4.10 would be better with my now shorter rear tire.

if you run a big cam with one of those aggressive(read touchy) clutches, you will love the shorter gearing. the low first gear of the t56 coupled with the 4 series rear gear makes the car pull out clean and effortlessly. with my big choppy cam and the original 3.73's, it took more clutch slippage to get the car moving.

Thanks for the input; Do you know the ratios for your T-56? I know that the Dodge version that I have is supposed to be geared differently than some of the others.

What are the rest of the specs on the engine? Mainly where is the powerband. I assume it is carbed so you are not going to want the rpm too low when in overdrive to avoid "lugging."

And what are your plans/goals with the car?

Those are important things too.

Those are good questions :) I'm not sure on exact power because I have not had it dynoed (I will most likely get it dynoed and tuned when I get the car driveable). I based the engine build loosely on one of the "engine recipes" from my pontiac engine building book - should be in the 450-500 hp range. Cam is solid, 525 lift, 280-290 range advertised duration. Yes, it's carbed, Holley 850 double pumper.

For use, mainly street and probably drag strip at first. I do want to get into autocross at some point.

Thanks again

what kind of power is that 461 making?
What will the car weigh with you in it?

3.89 would be a good choice IMO as your engine isn't super high revving..... but it does make a ton of torque down low.

I like this gear ratio calculator:
http://f-body.org/gears/ choose '98 M6 for the transmission

I ended up going with 4:11, guess we'll see how it goes.Thanks for all the input.

If it does not suit you, it's not the worst thing in the world to change out. :)

For sure; The difference between the two isn't all that much, on paper anyways. And I've got no problem swapping gears if I don't like it later on. The 4:11 just seems like it'll get all 6 speeds used more often.

You made the right call with the 4.11 and a 27" tire.:thumbsup: