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Does changing the rear gear ratio change the RWHP #?

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Old 01-18-2004, 07:09 PM   #1
mowrey96
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Default Does changing the rear gear ratio change the RWHP #and/or torque?

Does changing the rear gear ratio change the RWHP # and/or torque?

I assume that it would, but thought I would ask.

:steering:


[Modified by mowrey96, 7:11 PM 1/18/2004]
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Old 01-18-2004, 07:21 PM   #2
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

No,sir.Changing the gear ratio will not increase your horsepower.It allows you yo use your power at different ranges. :chevy :chevy :flag :chevy :chevy
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Old 01-18-2004, 07:22 PM   #3
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

Yes it does! I dynoed over 350 before I went from 3.42's to 3.73's, now I am around 340.
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Old 01-18-2004, 07:23 PM   #4
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (wallstAL)

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Yes it does! I dynoed over 350 before I went from 3.42's to 3.73's, now I am around 340.
Yep, you will lose RWHP going to taller gears. But, it sure doesn't feel like it!!!!
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Old 01-18-2004, 08:00 PM   #5
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (C5 StockSwap)

Can anyone explain the reason for this?
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Old 01-18-2004, 08:24 PM   #6
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (jmzvet)

ttt, since I would like to know also :confused:
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Old 01-18-2004, 08:48 PM   #7
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (jmzvet)

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Can anyone explain the reason for this?
That's an easy one: More friction loss :yesnod:
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Old 01-18-2004, 09:07 PM   #8
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (C5 StockSwap)

Your damn skippy. You do dyno lower #'s, but a dyno is not the street. Your not turning rollers on the street via rotating mass. back in the day a buddy had a tunnel rammed 327 with two 600 cfm holleys solid cam etc, we couldn't get it to stop boging on the dyno when we shifted it but on the street there was nothing but power.
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Old 01-18-2004, 09:28 PM   #9
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

Changing to a lower gear, 3.73, 4.10. or higher, increases the torque multiplication force applied to your rear wheels, but lessens the horsepower. Lower gears increase the rate at which power is applied, i.e., faster acceleration. Going to a higher gear reduces the rate of change , but increases the amount of power (power is a function of time) that can be put down, faster top speed, less change of rate (acceleration). It is just a simple engineering trade-off associated with auto dynamics.
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Old 01-18-2004, 10:19 PM   #10
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (Vette Lag)

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Changing to a lower gear, 3.73, 4.10. or higher, increases the torque multiplication force applied to your rear wheels, but lessens the horsepower. Lower gears increase the rate at which power is applied, i.e., faster acceleration. Going to a higher gear reduces the rate of change , but increases the amount of power (power is a function of time) that can be put down, faster top speed, less change of rate (acceleration). It is just a simple engineering trade-off associated with auto dynamics.
:iagree: :hurray: :hurray:
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Old 01-18-2004, 10:26 PM   #11
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

I think it also has to do with your 1 to 1 final drive ratio--bottom line no it does not affect your hp or tq it only appears to because it distorts the dyno readings, dyno in 3rd gear than dyno in 5th and see the diff-342 to 373 has shown about an 11rwhp loss, to 390s about 15 and 410s about 20---
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Old 01-19-2004, 01:45 AM   #12
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

Yes RWHP/RWTQ will change.

The engine will still be producing the same power, but when you go to a lower differential gear, the dyno will always show more torque and less horsepower.
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Old 01-19-2004, 11:51 AM   #13
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

Interesting responses. Didn't know you would lose HP, but it does make sense.
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Old 01-19-2004, 12:12 PM   #14
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (JDs00PewterCoupe)

With taller rear gears, the RWHP 'sees' more of the rotational inertia (of engine and driveline) than with standard gears. So, just like the HP numbers out of 1st and 2nd gears are lower than the HP numbers out of 4th, taller rear gears opperate similarly.
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Old 01-19-2004, 12:20 PM   #15
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (mowrey96)

HP is a measure of work done over time. Torque is instantaneous twisting force. So, with 4:10 gears the engine will have to do a little more work to move the wheels the same distance is would for 3:42 gears. Torque, on the other hand, will increase because the instantaneous twisting force of the bigger axle gear will be greater for the same amount of force applied to the pinion. You can gage it by the length of the skidmarks it puts in your shorts after you put 4:10's in. :reddevil
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Old 01-19-2004, 12:38 PM   #16
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (NEPTUNEBILL)

Quote:
but a dyno is not the street.
ding... ding... ding; we have a winner!
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Old 01-19-2004, 12:57 PM   #17
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (Mike Mercury)

My theoretical view: I believe with a smaller pinion gear relative to the ring gear, one has smaller area of instantaneous contact for given load. This leads to thinner film thickness of the lubricant. Thinner film thickness for given speed leads to higher velocity gradients across the gear lubricant. Higher velocity gradients for given viscosity means more shear losses. And that COULD explain the hp loss, yet not enough to offset the increased torque multiplication of a higher ratio gearset at lower wheel or road speeds.
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Old 01-19-2004, 01:14 PM   #18
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (ArKay99)

Quote:
You can gage it by the length of the skidmarks it puts in your shorts after you put 4:10's in. :reddevil
Now that is funny! :lolg: :lolg: :lolg: :lolg: :lolg: :lolg:
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Old 01-19-2004, 01:34 PM   #19
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (STAGED)

Quote:
My theoretical view: I believe with a smaller pinion gear relative to the ring gear, one has smaller area of instantaneous contact for given load. This leads to thinner film thickness of the lubricant. Thinner film thickness for given speed leads to higher velocity gradients across the gear lubricant. Higher velocity gradients for given viscosity means more shear losses. And that COULD explain the hp loss, yet not enough to offset the increased torque multiplication of a higher ratio gearset at lower wheel or road speeds.
Gearing is simply a matter of leverage. Albeit, continuous. :)
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Old 01-19-2004, 03:36 PM   #20
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Default Re: Does changing the rear gear ratio change the RWHP #and/or torque? (ArKay99)

You realize of course that the gearing differences are accounted for on the dyno. The goal of course is to dyno with a overall drive ratio of 1:1 for the most accurate comparison, but you enter all the info into the dyno computer and it eliminates gearing from the equation. It my opinion that the small loses from gear changes are frictional due to the higher engine/gear box/ driveshaft speeds required for any wheel rpm.
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