Acceleration difference with diff ratio's?

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Sep 22, 2009 | 02:01 PM

corvettedave383

Thread Starter

Burning Brakes

Joined: Apr 2008

Posts: 825

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From: Glasgow, Scotland

Acceleration difference with diff ratio's?

Anyone know the acceleration difference bewteen a 3.08 and a 3.55 diff ratio??(running a 350 turbo auto, with 450bhp 383)

cheers

dave

Sep 22, 2009 | 02:42 PM

bashcraft

Le Mans Master

Joined: Jan 2006

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From: Butler Pa

About 15% better.

Sep 22, 2009 | 04:25 PM

Glensgages

Race Director

Joined: Jan 2003

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From: State of Confusion

kind-of an open-ended question ('acceleration difference' ?), but I'll throw a few examples out.

My old Z28 came with 3.42 gears, and we got it to run 14.40s @ 97 MPH in the 1/4-mile:
a swap to 4.11s (and nothing-else) resulted in 14-teens at the same MPH

My '82 (2.87:1 gears) ran 16-ohs @ 82 MPH when it was dead-stock (heat of Summer, though), and after a late-October switch to 3.73s, it ran 15.20's @ 89 on a cold day in Taxylvania

hope this helps!

Sep 22, 2009 | 04:45 PM

captl27

Instructor

Joined: Jan 2006

Posts: 228

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From: Warwick New York

Of course you will have better acceleration but there are more variables. Does the trans have work. what tires are you running and whatever you add to the bottom end you take from the top. In your case I guess the top will not be a big loss. I think you will be happy with a change like you are talking about. He is a calculator that you can stick different gear ratios in and find out different information. Just stick in a 5 speed trans and use 4rth gear it is probably 1 to 1 like your auto.
http://www.keislerauto.com/speed_analyzers.php?sa=gm_5

Sep 22, 2009 | 06:17 PM

Ganey

Race Director

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From: CORVETTE 77 385 C.I. TEXAS

Dave

In a 1/4 a few tenths faster assuming you have traction- so you should consider current traction.

Sep 22, 2009 | 08:10 PM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

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From: Crossville TN

It will be better....until the tranny breaks. Hopefully, that THM350 has been beefed-up. If not, 450HP will mess it up pretty quickly. Sounds like fun, though.....

Sep 23, 2009 | 01:16 PM

corvettedave383

Thread Starter

Burning Brakes

Joined: Apr 2008

Posts: 825

Likes: 40

From: Glasgow, Scotland

Thanks guys for your thoughts, my old diff has got loads of problems, leaking front seal, one of the holes for mounting the leaf spring to the diff, is broken, the yokes are flopping about everywhere, so overdue for a newer one

cheers

dave

Sep 23, 2009 | 02:49 PM

larrywalk

Melting Slicks

Joined: Oct 2002

Posts: 2,317

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From: St Louis MO

Quote:

Originally Posted by corvettedave383

Anyone know the acceleration difference bewteen a 3.08 and a 3.55 diff ratio??(running a 350 turbo auto, with 450bhp 383)

cheers

dave

The difference between the ratios is 15%, so there will be that much more torque available. Whether or not you can put it all to the ground is another matter.

I ran a simulation program recently to figure whether I ought to get a lower rear end gear instead of my 3.08. With my setup (see my profile), I've done a best of 11.599 at 118.9, but the program predicted approximately a .1 second improvement with each 10% reduction, i.e., 11.50 with a 3.36; 11.40 with a 3.70, and 11.30 with a 4.11. However, the speed leveled off at 120 with no further improvement.

In another consideration besides putting it all down is the strength of the rear end parts - I'm not yet ready to step up to a custom rear end setup.