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Old 05-05-2010, 09:20 PM
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Differential gears to match Saginaw trans.

ok, I have a 360 chevy that has a dynamic compression ratio around 9-9.5:1 that has most of it's power in the mid to low end of rpms. I'm planning on drifting this vehicle constantly. I have a 4 speed saginaw (no line) high gear ratio trans with the stock 2.73 rear end. I'm trying to find some sort of calculator to figure out what the best set of gears would be to go along with the high gear trans... anyone have any ideas? Thanks!

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Old 05-06-2010, 04:56 AM
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The gear ratios for the Saginaw I have are... "No lines - 1st = 2.84, 2nd = 2.01, 3rd = 1.35 and 4th = 1.00.
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Old 05-06-2010, 06:06 AM
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I got this off of a Lexus forum but anyways this is basic information. Does anyone agree with this or is this aimed towards boosted motors only or is this not even accurate?

"In general, the standard convention is to choose a rear gear that will put your total first gear ratio between 10:1 and 11:1. For the stock 4AT (Gear 1 = 2.804), a total first gear ratio of 10:1 to 11:1 would be achieved with a rear gear of 3.57-3.92." http://www.clublexus.com/forums/perf...my-swap-2.html

If that were true, for my setup I would want a 3.73?

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Old 05-06-2010, 06:13 AM
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^^That's pretty close to the numbers I have as well (1st=2.85, 2nd=2.02, 3rd=1.35, 4th=1.00)
I had a '68 Elky that was a factory 307/2-groove Saginaw, 3.08 non-posi.
The 2-groove (3.11 1st-gear) was a good match for the 3.08 rear. You wouldn't win many races, but it was a good daily-driver set-up. With your 2.85-first, you might want to consider something in the mid-3's rear-gear? That's for streetabilty though. Drifting is another story...
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Old 05-06-2010, 06:19 AM
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Quote:
Originally Posted by Caballerokid
I got this off of a Lexus forum but anyways this is basic information. Does anyone agree with this or is this aimed towards boosted motors only or is this not even accurate?

"In general, the standard convention is to choose a rear gear that will put your total first gear ratio between 10:1 and 11:1. For the stock 4AT (Gear 1 = 2.804), a total first gear ratio of 10:1 to 11:1 would be achieved with a rear gear of 3.57-3.92." http://www.clublexus.com/forums/perf...my-swap-2.html

If that were true, for my setup I would want a 3.73?
If you are looking to get to 10-11:1 you need to go way steeper than a 3.73 with that 2.84 first gear.

EDIT: I was way off with my math, that combo does put you there.
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Old 05-06-2010, 06:31 AM
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That's what I was wondering... do I want to be in that 10:1-11:1 ratio by choosing a rear gear matched with the 1st gear ratio of the trans? Or is that wrong thinking?... and since I am going to be drifting, I need break-wheel power on demand, would I still want to be in that ratio window? Or somewhere completely different? I know this may be kind of an odd request...
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Old 05-06-2010, 06:33 AM
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The tires I have right now have a diameter of 25.57" and a circumfrence of 80.29". Just so I have all the information posted...
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Old 05-06-2010, 06:38 AM
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Trial and error might be your best shot. If you're familiar with the area you're drifting, you'll know at least what gear you should be in (I'm guessing second-gear for a faster course?). But just as a starting-point, a mid-to-high 3-series gear is best for street use.
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