3.73 or 3.90 Gears?
Thread Starter
Burning Brakes
Joined: Sep 2004
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From: www.shockerracing.com
3.73 or 3.90 Gears?
My buddy has a 2000 FRC MN6 with heads/cam/headers and he is having his rear end rebuilt. He is trying to decide whether to go with a 3.73 or 3.90 gear. I do not know anyone who has put a 3.73 in a Corvette, it seems the majority go with the 3.90 and love it. Does anyone have any thoughts about the 3.73 gears as far as how it will perform at the dragstrip in comparison to the 3.90? Any help is greatly appreciated!
Race Director
Joined: Aug 2006
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From: Are you fat because you're lazy or lazy because you're fat? San Jose, CA
Cruise-In X Veteran
St. Jude Donor '09
Go with the 3.90, it's not worth going to the 3.73 from the 3.42.
The only reason I can think of against the 3.90 would be if he has a really stout H/C package pushing over 450rwhp.
Either way, 3.90 should be the choice.
The only reason I can think of against the 3.90 would be if he has a really stout H/C package pushing over 450rwhp.
Either way, 3.90 should be the choice.
Le Mans Master
Joined: Jun 2004
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From: The Arid Sunny Desert
Le Mans Master
Joined: Feb 2001
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From: West "By God" Virginia
CI 7-8-9-10 Veteran
I'm in kinda the same boat. After seeing some 410 geared cars run at the CI, I want some gears for my Z. I was originally thinking 390's, b/c the mn12 is geared differently, but I have 450 whp na, and a 100 shot on top of that. So now, I am thinking 373's, even though that is not a huge jump, I think with my cam and my style of driving, 373's would put me in a better rpm range. I don't know, let me know what he decides though and how he likes it!!
Pro
Joined: Jan 2005
Posts: 559
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From: Lenexa Kansas
I have a 99 FRC with a head/cam job (410whp), and I'm thinking about dropping the gears as well, because of those pesky MN12's in the stock Z06's; their gearing gives them a rate of acceleration in a given gear equal to a much higher hp MN6, although they have to go up to the next gear sooner.
I have a neat spreadsheet an engineer buddy of mine worked up for me, and it factors in two cars' torque curves, weights, drag, tire diameter, gears, rear diff's, etc... It gives you an estimated level of acceleration for various setups. I liked the looks of the 3.90's over the 3.73's, because it gets the MN6's gearing more in line with the MN12's.
I have a neat spreadsheet an engineer buddy of mine worked up for me, and it factors in two cars' torque curves, weights, drag, tire diameter, gears, rear diff's, etc... It gives you an estimated level of acceleration for various setups. I liked the looks of the 3.90's over the 3.73's, because it gets the MN6's gearing more in line with the MN12's.
Le Mans Master
Joined: Feb 2001
Posts: 6,777
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From: West "By God" Virginia
CI 7-8-9-10 Veteran
I have a 99 FRC with a head/cam job (410whp), and I'm thinking about dropping the gears as well, because of those pesky MN12's in the stock Z06's; their gearing gives them a rate of acceleration in a given gear equal to a much higher hp MN6, although they have to go up to the next gear sooner.
I have a neat spreadsheet an engineer buddy of mine worked up for me, and it factors in two cars' torque curves, weights, drag, tire diameter, gears, rear diff's, etc... It gives you an estimated level of acceleration for various setups. I liked the looks of the 3.90's over the 3.73's, because it gets the MN6's gearing more in line with the MN12's.
I have a neat spreadsheet an engineer buddy of mine worked up for me, and it factors in two cars' torque curves, weights, drag, tire diameter, gears, rear diff's, etc... It gives you an estimated level of acceleration for various setups. I liked the looks of the 3.90's over the 3.73's, because it gets the MN6's gearing more in line with the MN12's.
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Le Mans Master
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From: In the pit, trying to love someone.
Melting Slicks
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From: Westchester County New York
Le Mans Master
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From: West "By God" Virginia
CI 7-8-9-10 Veteran
Again, I will ask...
^It was a question Mike, not an assumption. Per the chart he has, I would like to know what an mn12 w/373's would be equivilent to with an mn6 w/390's, 410's, or what???
Team Owner
Joined: Jul 2004
Posts: 24,652
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From: NJ
St. Jude Donor '05-'08
Remember with the MN12 it is only the first 3 gears that are affected and then after that it is the same as the mn6.
I have 3.73s because I road race. I tried 4.10s, but they are just not good on a road course. If I wasnt doing road racing though I would have 4.10s in the car because they are more fun on the street.
I have 3.73s because I road race. I tried 4.10s, but they are just not good on a road course. If I wasnt doing road racing though I would have 4.10s in the car because they are more fun on the street.
Pro
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From: Orlando FL
Race Director
Joined: Mar 2007
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From: Marlton. Increasing performance one speeding ticket at a time! NJ
1st 2.66 = 9.92/10.37/10.9
2nd 1.78 = 6.6/6.94/7.63
3rd 1.30 = 4.85/5.07/5.33
4th 1.0 = 3.73/3.9/4.1
5th .74 = 2.76/2.88/3.03
6th .50 = 1.87/1.95/2.05
Rev. 2.9
MN12 @ 3.42/3.73
1st 2.97 = 10.16/11.08
2nd 2.07 = 7.08/7.72
3rd 1.43 = 4.89/5.33
4th 1.0 = 3.42/3.73
5th .84 = 2.87/3.13
6th .56 = 1.92/2.08
Rev. 3.28
Depends on the gear, but 3.42 on the MN12 falls somewhat between 3.73 and 3.90 on the MN6 with 2nd being much shorter and 4th much taller. For 1/4mile acceleration purposes, I think it compares more closely to 3.90's on the MN6.
Last edited by nj02vette; Jun 2, 2007 at 10:40 AM.
Race Director
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From: Marlton. Increasing performance one speeding ticket at a time! NJ
Drifting
Joined: Dec 2001
Posts: 1,808
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From: Little Rock, AR
MN6 @ 3.73/3.90/4.10
1st 2.66 = 9.92/10.37/10.9
2nd 1.78 = 6.6/6.94/7.63
3rd 1.30 = 4.85/5.07/5.33
4th 1.0 = 3.73/3.9/4.1
5th .74 = 2.76/2.88/3.03
6th .50 = 1.87/1.95/2.05
Rev. 2.9
MN12 @ 3.42/3.73
1st 2.97 = 10.16/11.08
2nd 2.07 = 7.08/7.72
3rd 1.43 = 4.89/5.33
4th 1.0 = 3.42/3.73
5th .84 = 2.87/3.13
6th .56 = 1.92/2.08
Rev. 3.28
Depends on the gear, but 3.42 on the MN12 falls somewhat between 3.73 and 3.90 on the MN6 with 2nd being much shorter and 4th much taller. For 1/4mile acceleration purposes, I think it compares more closely to 3.90's on the MN6.
1st 2.66 = 9.92/10.37/10.9
2nd 1.78 = 6.6/6.94/7.63
3rd 1.30 = 4.85/5.07/5.33
4th 1.0 = 3.73/3.9/4.1
5th .74 = 2.76/2.88/3.03
6th .50 = 1.87/1.95/2.05
Rev. 2.9
MN12 @ 3.42/3.73
1st 2.97 = 10.16/11.08
2nd 2.07 = 7.08/7.72
3rd 1.43 = 4.89/5.33
4th 1.0 = 3.42/3.73
5th .84 = 2.87/3.13
6th .56 = 1.92/2.08
Rev. 3.28
Depends on the gear, but 3.42 on the MN12 falls somewhat between 3.73 and 3.90 on the MN6 with 2nd being much shorter and 4th much taller. For 1/4mile acceleration purposes, I think it compares more closely to 3.90's on the MN6.
Good news! I just bought 3.90's and was wondering about top speed. Since 5th gear is almost identical, MN6-3.90 to MN12-3.42 then my top speed in 5th should be roughly the same as a Z06 if I raise the RPM limiter to the Z06 redline. Cool!
Instructor
Joined: Dec 2004
Posts: 184
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From: Middletown DE
I am on the fence between 3.90's and 4.10's. I currently have about 405 rwhp, with plans to do heads down the line. Looking for mostly spirited street driven fun
Any opinions?
Also, I have read some posts that say 1st gear is useless with 4.10's ??
Any opinions?Also, I have read some posts that say 1st gear is useless with 4.10's ??
Le Mans Master
Joined: Jun 2002
Posts: 8,352
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From: In the pit, trying to love someone.
With power adders or heads/cam, yes. On a basically stock or bolt on car, 4.10's are fine. I have 3.90's right now and I'm thinking of going down to 3.73's or back to 3.42's with the extra torque from my stroker.