[1966 chevelle 502]

Hey guys.

I have just made an order for my street / strip ( mostly strip )on a complet M9 rear end for my 70 chevelle. I decided to go with the 3,89 gear ratio but now i´m wondering if it should have been a 3,75 or maybe even a 3,50 gear ratio instead.

So I thougth maybe you guys could help

The car is ligthend but dont got the exact weigth on the car ( kirkey seats , removed collision doorbars , bbc with aluminum heads , aluminum radiator, removed front inner wheel whels , removed ac + power steering )

It has a 582 bbc with peak hp at 6000rpm and want to cross the 1/4 mile at MAX 6400rpm in third gear ( 752 hp on motor and 733 tq on motor ) th400 and going to run 28" drag radials. Mostly going to run 1/8 mile but a couple of times a year it will see the 1/4 mile track.

Wich would be the better rear gear-ratio choice

Thanks

 

[mfret1970]

You did mention this car May see some street time as well, so I think I'd gear for street time/1/4mi versus gearing it to run quickest in the 1/8. Do you have the dyno sheet? There are a number of calculators online. You want to gear it so you're just passed peak hp as you cross the stripe. So, if it peaks at 6200rpm you would want to cross at around 6600. With 750hp, you've got the nuts to run mid to low 10's, so I'd probably use a mph figure of 135mph to plug into the calculator. Whatever gear puts you at 135mph at an rpm just over peak hp is where you'll want to be.


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[72BBMonte]

Do you know where motor made peak power and how many rpm you are willing to turn it? Of the three choices you gave the gear you bought is best IMO for strip use without further data. :thumbsup:

 

[1966 chevelle 502]

Thanks for the quick respons guys

motor data:

It has a 582 bbc with peak hp at 6000rpm and peak tq at 4800rpm , want to cross the 1/4 mile at MAX 6400rpm in third gear ( 752 hp on motor and 733 tq on motor )

Thanks

 

[1966 chevelle 502]

You did mention this car May see some street time as well, so I think I'd gear for street time/1/4mi versus gearing it to run quickest in the 1/8. Do you have the dyno sheet? There are a number of calculators online. You want to gear it so you're just passed peak hp as you cross the stripe. So, if it peaks at 6200rpm you would want to cross at around 6600. With 750hp, you've got the nuts to run mid to low 10's, so I'd probably use a mph figure of 135mph to plug into the calculator. Whatever gear puts you at 135mph at an rpm just over peak hp is where you'll want to be.

So I tried the online wallace racing calculater and it seems like the 3,89 ratio would be fine.

Thanks :thumbsup:


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Do you know where motor made peak power and how many rpm you are willing to turn it? Of the three choices you gave the gear you bought is best IMO for strip use without further data. :thumbsup:

I think 6400rpm is around MAX that i would want to rev it and with my peak hp at 6000rpm it seems like the 3,89 is the way to go.

Thanks

 

[CDN SS]

What size rear tire ? 3.89 look right to me with at least a 28" tire for sure with 30" you can adjust with tire height find a calc and do the math then you know for sure

 

[1966 chevelle 502]

What size rear tire ? 3.89 look right to me with at least a 28" tire for sure with 30" you can adjust with tire height find a calc and do the math then you know for sure

The tires are 28" MT drag radials. Just did the online calculater and just like you and the other guys say it looks like the 3,89 ratio is the way to go.

Thanks

 

[crazydavey]

The tires are 28" MT drag radials. Just did the online calculater and just like you and the other guys say it looks like the 3,89 ratio is the way to go.

Thanks

3.89's with a 29x10.5 on mine is pulling about 67/6800 at the stripe on a good pass.......

 

[mfret1970]

I think 6400rpm is around MAX that i would want to rev it and with my peak hp at 6000rpm it seems like the 3,89 is the way to go.

Thanks

Sounds good. Now get it to the track and let us know how it runs!


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[1966 chevelle 502]

3.89's with a 29x10.5 on mine is pulling about 67/6800 at the stripe on a good pass.......

I dont think my car will ever run as good as yours Davey :thumbsup:

Is it possible to fit a 30" tire i a stock 70 chevelle rear wheel well ? Then I could run 30" tires when I run the 1/4 mile so the rpm dont get to high.

 

[1966 chevelle 502]

Sounds good. Now get it to the track and let us know how it runs!


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I sure will :yes:

 

[crazydavey]

I dont think my car will ever run as good as yours Davey :thumbsup:

Is it possible to fit a 30" tire i a stock 70 chevelle rear wheel well ? Then I could run 30" tires when I run the 1/4 mile so the rpm dont get to high.

well Jimmi is those power numbers are correct it should run very good...I think you would be pulling close to the same rpm's. A 30" tire would be very tight, some of the guys are running a 29.5 but with a radial that doesn't "grow". If you want to keep it below 6400 I would go with the 73's...

 

[1966 chevelle 502]

well Jimmi is those power numbers are correct it should run very good...I think you would be pulling close to the same rpm's. A 30" tire would be very tight, some of the guys are running a 29.5 but with a radial that doesn't "grow". If you want to keep it below 6400 I would go with the 73's...

I think that I will try with a 28" drag radial and the 3,89 when I run the 1/8 mile and for the 1/4 mile track i will run a 29,5" radial and if it pulls to many rpm´s on the 1/4 I guess Straub will have to make me a cam and lifter deal :thumbsup:

I got the power numbers from the engine builder ... havent dyno the motor my self.