gear ratio formula
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Joined: Nov 2011
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From: Indiana
gear ratio formula
having an old man moment but can not remember if I'm thinking right or not. At one time I thought I read that to get optimum performance the 1st gear ratio multiplied by rear ratio was suppose to be around 10 for 4 speed transmissions. Is this correct or am I thinking of some other formula? Thanks, Tom
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Advanced
Joined: Nov 2011
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From: Indiana
Thread Starter
Advanced
Joined: Nov 2011
Posts: 95
Likes: 6
From: Indiana
Burning Brakes
Joined: Oct 2009
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having an old man moment but can not remember if I'm thinking right or not. At one time I thought I read that to get optimum performance the 1st gear ratio multiplied by rear ratio was suppose to be around 10 for 4 speed transmissions. Is this correct or am I thinking of some other formula? Thanks, Tom
Thanks
Drifting
Joined: Oct 2012
Posts: 1,524
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From: Medina Ohio
Burning Brakes
Joined: Oct 2009
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less than 10 = better for highway
more than 10 = better off the line
Is this correct?
Thanks
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Drifting
Joined: Oct 2012
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From: Medina Ohio
So say you had a TH350 trans and a 3.08 rear end. First gear in a Turbo 350 is 2.52. Literally multiply it by the rear gear, say 3.08 = 7.76 (Dog off the line, great highway)
Same trans with a 3.73 gear = 9.39 (pretty good off line performance, a bit high on the highway) ...with 4.11 = 10.35
Once people grasp the final drive ratios (in first and last gear), its easier to see the benefits of the OD trannys. With the TKO, you can have a fairly mild rear end, still have great off the line and low cruise RPM.
TKO 600 5 speed
2.87 x 3.36 = 9.64
2.87 x 3.55 = 10.18
2.87 x 3.73 = 10.70
etc. etc. etc.
You can use the same multiplication formula for final drive ratio in your highest numerical gear. 3rd in a 3 speed etc. The 3 speed autos, and 4 speed sticks are 1:1, so whatever your rear gear, is your final drive. With the OD, take its ratio (either .64 or .82 for the TKO 600) and multiple it by the rear gear.
.64 x 3.55 is like a 2.27 rear gear on the highway in a 3 or 4 speed car.
.82 x 3.55 = 2.91
Last edited by Ibanez540r; Nov 21, 2016 at 01:32 AM.
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From: Corsicana, Tx
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You're asking about 1st gear. Once you shift..it doesn't affect the top speed. I know what you're talking about, but just wanted to clarify things. "IF" you can get more first gear in the trans it allows you to play with rear gears a little more unless the gear spread gets too large on the shifts. There are some BW Super T-10's with a 2.88 first gear that helps with 3.08's.
Meaning...you can use a trans with a lot deeper 1st gear and still have the 3.08's and have best of both worlds. That's where the Richmond 5 and 6 speeds come in.
I've got 3.07 rear gears....but I've also got a 3.39 first gear. Makes for a 10.4 first gear ratio. I wish it had a little more, but I've got 28" tall tires too.
Of course I've also got 1140 RWHP to help it along!!
JIM
Meaning...you can use a trans with a lot deeper 1st gear and still have the 3.08's and have best of both worlds. That's where the Richmond 5 and 6 speeds come in.
I've got 3.07 rear gears....but I've also got a 3.39 first gear. Makes for a 10.4 first gear ratio. I wish it had a little more, but I've got 28" tall tires too.
Of course I've also got 1140 RWHP to help it along!!
JIM
Instructor
Joined: Sep 2015
Posts: 216
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From: Haverfordwest Pembrokeshire
Have a look at Autogear, I've just put one of their M22W sets in my Muncie to go with a 3.55 rear in my 350/350 gives a first gear figure of 9.088 so your 454 should be happy with that combination.
Had to change as Muncie needed a rebuild and I had a 4.56 rear end which was like driving round in 2nd gear all the time, great for takeoffs but no fun on the open road!
Just finished putting the gearbox back together next job is the diff once the gearbox is back in the car.
Graham
Had to change as Muncie needed a rebuild and I had a 4.56 rear end which was like driving round in 2nd gear all the time, great for takeoffs but no fun on the open road!
Just finished putting the gearbox back together next job is the diff once the gearbox is back in the car.
Graham
Safety Car
Joined: Sep 2007
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From: Indy Indiana
the factory built mostly 3:08 or 3:36 with the 2.52 1st gear muncie.
comes to 8.46 or 7.76 . not the 10 as suggested above. it you want good all around compromise, then around 8 is what you want.
with a multiple equal to 10.. then 1st gear is pretty much just a granny gear..
comes to 8.46 or 7.76 . not the 10 as suggested above. it you want good all around compromise, then around 8 is what you want.
with a multiple equal to 10.. then 1st gear is pretty much just a granny gear..
Thread Starter
Advanced
Joined: Nov 2011
Posts: 95
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From: Indiana
the factory built mostly 3:08 or 3:36 with the 2.52 1st gear muncie.
comes to 8.46 or 7.76 . not the 10 as suggested above. it you want good all around compromise, then around 8 is what you want.
with a multiple equal to 10.. then 1st gear is pretty much just a granny gear..
comes to 8.46 or 7.76 . not the 10 as suggested above. it you want good all around compromise, then around 8 is what you want.
with a multiple equal to 10.. then 1st gear is pretty much just a granny gear..
Team Owner
Joined: Apr 1999
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From: Reno Nevada
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It is not cheap to change rearend gear ratios. I just did one for a client and I had over $1300 in just parts. Went with US gears, eaton posi unit was $680, complete bearing/shim kit was $250.
Here is an example of prices. https://www.ringpinion.com/DiffWizard.aspx just put in your year and model.
Like jim above said the better choice in transmissions is something with lower first gearing like the richmonds.
I went with OD transmissions and 4.11 rear end for over 20 years. My 5 speed TKO 600 has a 2.87 first and combined with a 4.11 makes for 11.7957 first gear ratio. It really worked well with my 427ci. I personally like over 10 because you hardly have to slip the clutch to take off and never bog the engine.