Need help with rear axle ratios

[IH2LOSE]

Some of you guys know I am building a hybrid car.I need to determin a nice rear axle ratio.

My 66 presently has a M21 with 4:11s in it and I love the out of the hole pull but hate the highway RPMS. I have a 3:36 I plan on installing as soon as I get a free week end. I never drove the car with the 3:36's and I am hoping I like it.

Anyways I am building the hybrid car as a cruiser. I am installing a 700R trans and the ratios are (1st 3.06:1) I was told this is a real low gear,(2nd 1.62:1), (3rd 1:1), (4th 0.70:1) I hope to be running the tires off of my C5 P275/40ZR18 REAR (Hopefully John Magraw had said they may be TOO BIG) if they dont fit then I would use P245/45ZR17 I had thought i would be using a 3;73 rear to take advantage of the over drive of this transmition but it seems the steepest stock ration of a dana 44 is 3:55's does anybody know what rear ratio I would use to give the same out of the hole pull my 66 is giving me with the 4:11 I have in it now.

Does anybody know what the first gear is in my M21 (it was rebuilt to stock specs by Ed Hartnet)

Thanks Again

 

[Sky65]

I beleive the M21 gear ratios are 1st 2:20:1, 2nd 1.64:1, 3rd 1.28:1, 4th 1:1

This site may help you with your final drive ratio. I use Tire Rack to get the tire diameter number.

http://www.quiknet.com/~ke6vut/rpmcalc.html
http://www.tirerack.com/

 

[Gerry]

You can also look at www.keislerauto.com for neat calculations of gear ratios and speed.

Best regards,
Gerry

 

[John Mcgraw]

Larry,

Even with 3.36 gears, the final drive ratio will exceed the drive ratio on your M21 with 4.11 gears! The final drive ratio of this setup in first gear is 9.042:1 while the final ratio of the R700 with 3.55 gears is 10.969:1. I went to 3.54:1 gears on my 59, but this is probably overkill for a cruiser. The rear came with 2.59:1 gears in it and I just could not leave them in!

Regards, John McGraw

 

[Mikey1]

Chekout for the right combination of gearbox and axle ratio.

If you use a 6spd Keisler/Tremec combo and a 2.73 rearend you are able to have a nice accelaration and good highway cruise low rpm's.

 

[Gerry]

If the car is a midyear then the six speed will not fit without cutting, however the five speed will and gives the best of all worlds with a 3:36, 3:54 or 3:70. That's what I am putting in my 67 BB.

Best regards,
Gerry

 

[00fxd]

Gerry I can't find the calculator on the Keisler site. I've used it before but maybe it's gone?

 

[Islander]

Gerry I can't find the calculator on the Keisler site. I've used it before but maybe it's gone?

Try this link and scroll all the way down past the picture of the tranny:

http://www.keislerauto.com/gm/transmissions/corvette_63-67.asp

 

[00fxd]

Thats it Islander, Thanks. Looks just like my car too!

 

[Mikey1]

Chekout for the right combination of gearbox and axle ratio.

If you use a 6spd Keisler/Tremec combo and a 2.73 rearend you are able to have a nice accelaration and good highway cruise low rpm's.

Yes...you are right.....but IH"LOSE was talking about a hybird car with an R700 tranny. So that was just a proposal of doing it another way.

Maybe a good rule of thum is that for a good acceleration your total 1st gear ratio should be something like 10ish (multiplied...).

 

[bossvette]

I have a Tremec TKO 5 speed and 3:36 and first gear is fine

 

[IH2LOSE]

So do you guys think I should stay with a set of 3;36's Max I really want a highwath cruiser in top gear But a real hard lanch stop light to stop light.



The next thing I need some type of an understanding on is the stall of a torgue converter.

 

[Mikey1]

Do you still want to stick with the R700 or are you prepared to change to a manual gearbox ?

 

[bossvette]

So do you guys think I should stay with a set of 3;36's Max I really want a highwath cruiser in top gear But a real hard lanch stop light to stop light.



The next thing I need some type of an understanding on is the stall of a torgue converter.

2000 RPM is in the neighborhood of 75mph with 3:36 and 275-60 -15 on the back as far as stall pick the converter company you want to deal with and call them with the details of your car and how you intend to drive it. they know the best and won't steer you wrong.

 

[John Mcgraw]

Larry,

I would think that the 3.36 or 3.54 would get you all the first gear grunt you will ever need, especially with that monster bigblock. If it was going to be a stop light bandit that seldom made it to the highway, then 3.73 would be more in line.
Regards, John McGraw

 

[IH2LOSE]

Larry,

I would think that the 3.36 or 3.54 would get you all the first gear grunt you will ever need, especially with that monster bigblock. If it was going to be a stop light bandit that seldom made it to the highway, then 3.73 would be more in line.
Regards, John McGraw

Thanks guys 3:36 or the 3:54's it will be.

As for the auto over the stick

I have a failing knees so an automatic is mandatory for future use.I could not drive my 66 for about 9 months after my last surgery.

 

[Gerry]

Thanks guys 3:36 or the 3:54's it will be.

As for the auto over the stick

I have a failing knees so an automatic is mandatory for future use.I could not drive my 66 for about 9 months after my last surgery.

Good luck with your hybrid, I think the 3:36 will do you fine especially as others have said "with that torque monster motor".

Best regards,
Gerry

 

[IH2LOSE]

Well I have my dana on order for a pick up in carlilse.I hope I did not make a mistake but the fellow who is warming up the engine said I HAVE to go with the 3:73's because other wise the engine would constantly be "lugging" with the lower rear end gears gears (below 3:73'S).

He explained the car would be a dog.I explained I wanted a cruiser and he said I should then build a cruser motor (whitch he said would be a low compression 454)And that the LS6 motor would better serve a racer.He also had reservation of the 700r4 behind the motor but I WILL NOT visit that again.

He also explained no mater what big block I used I would have a great out of the hole pull with the 700r4 trans but with the high gears its going to lug on the highway and will always be in the wrong rpm range.He said even with the taller rear gear we ordered I will still be "lugging at high way speeds"And I will always be pulling it down to a lower gear.( funny what he is explaining is excactly how I feel driving my C5 that is an automatic) So I ordered the 3:73's