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Old 07-13-2018, 05:08 PM   #1
GTOROB
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Gears

Having a hard time deciding which gears to go with 373's or 390's.

Doing gears for the short term just to change things up a bit and will be swapping again when my turbos go on.

416 stroker making 523/507

Don't do any drag racing,street car only.

I've never swapped gears before,but have read they really make a difference so wanting to give it a go.

Is there really a much noticeable difference over stock gears switching to 373's?

Last edited by GTOROB; 07-13-2018 at 05:11 PM.
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Old 07-13-2018, 09:14 PM   #2
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I dunno but if my calcs are right the .73s give and 8% increase and the .91s give an 13% increase over stock which I think is 3.46.

Something that's on my list too and based on feedback I've seen I'd go the .73 route. For the M6 cars the .93s make 1st gear useless. For you it should feel like adding a 40 hp or so bolt on. Of course rpm will be higher as will the rpm you cruise at on the highway and mpgs will drop some but doesn't like a factor to you.
When you go forced you'll want to go with taller gears so maybe go all out with the .93s while you're n/a knowing its temporary?
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Old 07-14-2018, 12:37 AM   #3
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I have been thinking about doing 3.91s for a while. Only drawback is I don't want the whining sound. If someone can point me to some Aussie gears I'd be most grateful. Sorry to threadjack.Have you decided where you would get the gears from? By the way, 403ci M6.
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Old 07-14-2018, 08:35 AM   #4
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3.91s
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Old 07-14-2018, 09:06 AM   #5
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Quote:
Originally Posted by HMBLGOAT...View Post
I dunno but if my calcs are right the .73s give and 8% increase and the .91s give an 13% increase over stock which I think is 3.46.

Something that's on my list too and based on feedback I've seen I'd go the .73 route. For the M6 cars the .93s make 1st gear useless. For you it should feel like adding a 40 hp or so bolt on. Of course rpm will be higher as will the rpm you cruise at on the highway and mpgs will drop some but doesn't like a factor to you.
When you go forced you'll want to go with taller gears so maybe go all out with the .93s while you're n/a knowing its temporary?


Yeah I know I'll have to swap again for the turbos. I think I'm gonna go with the 3.90's for the extra get off.
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Old 07-14-2018, 09:07 AM   #6
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Quote:
Originally Posted by Charm City...View Post
I have been thinking about doing 3.91s for a while. Only drawback is I don't want the whining sound. If someone can point me to some Aussie gears I'd be most grateful. Sorry to threadjack.Have you decided where you would get the gears from? By the way, 403ci M6.

I'm buying a used set from my engine builder,my exhaust will overpower the whine if I have any.

Last edited by GTOROB; 07-14-2018 at 12:28 PM.
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Old 07-14-2018, 01:24 PM   #7
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Quote:
Originally Posted by Charm City...View Post
I have been thinking about doing 3.91s for a while. Only drawback is I don't want the whining sound. If someone can point me to some Aussie gears I'd be most grateful. Sorry to threadjack.Have you decided where you would get the gears from? By the way, 403ci M6.

I believe Complete Street Performance has the Aussie gears.
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Old 07-22-2018, 09:54 AM   #8
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I've decided on the 3.90's and have install setup for first of August.
Think I'll have traction issues with 523/507 to the ground?

I have Billet Specialtie 15x10's on the way with 275/50 MT R's.
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Old 07-22-2018, 10:19 AM   #9
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Quote:
Originally Posted by GTOROB...View Post
I'm buying a used set from my engine builder,my exhaust will overpower the whine if I have any.

If it whines, you’ll hear it.
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Old 07-22-2018, 11:04 AM   #10
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Quote:
Originally Posted by jbo'sgoat...View Post
If it whines, you’ll hear it.

No biggie.
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Old 08-01-2018, 07:25 AM   #11
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At what speed do 3.90's top out at around 6500 rpms? Dropping my car off tomorrow for gear install.

Have the option for the 3.73's as well,but leaning towards 3.90's.

Street car only with no time at the drag strip,occassional roll races though.
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Old 08-01-2018, 08:22 AM   #12
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Here you go bud, can play around to your heart's content

http://www.wallaceracing.com/calc-rpm.php

EDIT:

This might actually make it easier for what you're trying to do.

http://www.wallaceracing.com/gear-speed.php

@6500rpms

3.46 - 145mph
3.73 - 135mph
3.90 - 129mph
4.10 - 123mph

Last edited by cookmeup272; 08-01-2018 at 08:24 AM.
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Old 08-01-2018, 03:50 PM   #13
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Quote:
Originally Posted by cookmeup272...View Post
Here you go bud, can play around to your heart's content

http://www.wallaceracing.com/calc-rpm.php

EDIT:

This might actually make it easier for what you're trying to do.

http://www.wallaceracing.com/gear-speed.php

@6500rpms

3.46 - 145mph
3.73 - 135mph
3.90 - 129mph
4.10 - 123mph

Thanks!
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Old 08-01-2018, 05:10 PM   #14
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Quote:
Originally Posted by HMBLGOAT...View Post
...For the M6 cars the .93s make 1st gear useless. ...

As someone who has a M6 with 3.91s, I'd disagree.

Quote:
Originally Posted by cookmeup272...View Post
http://www.wallaceracing.com/gear-speed.php

@6500rpms

3.46 - 145mph
3.73 - 135mph
3.90 - 129mph
4.10 - 123mph

Keep in mind the M6 has two extra gears beyond the 1:1 4th gear, so the theoretical top speed is higher than what you've calculated. The 6th gear is 0.57:1.
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Old 08-01-2018, 05:17 PM   #15
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For some reason I completely skipped over the two times he said "no drag racing" because I just assumed he was talking about what speed to cross the 1/4 at in 4th gear, whoops.
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Old 08-03-2018, 07:45 PM   #16
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Dropped my car off to get the 3.90's installed, hope I made the right choice.
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Old 08-03-2018, 09:43 PM   #17
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Quote:
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Dropped my car off to get the 3.90's installed, hope I made the right choice.

Absolutely the right choice, you’re gonna love them. You can roll in 5th at 25mph, didn’t even use 4th gear driving around town or even getting on the freeway. Never really beat on the car much or at all but for a daily and bolt ons only I’d go through tires like a mofo.
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Old 08-05-2018, 02:10 PM   #18
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Got the auto and went with 3.91's a few years ago. It's like night and day compared to the stock gears.
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Old 08-05-2018, 02:39 PM   #19
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Adding a TruTrac as well,car will be ready for pick up mid week.
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Old 08-11-2018, 02:24 PM   #20
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Picked up my car today after install and now have ABS fault and no traction control.

Think I've read issues with axle/stub play with a TruTrac can cause this,but don't know.

Can't figure it out so may just swap TruTrac back out for stock.

Anyone ever had this issue? I never had it before the gear swap.
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Old 08-11-2018, 05:51 PM   #21
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Quote:
Originally Posted by GTOROB...View Post
Picked up my car today after install and now have ABS fault and no traction control.

Think I've read issues with axle/stub play with a TruTrac can cause this,but don't know.

Can't figure it out so may just swap TruTrac back out for stock.

Anyone ever had this issue? I never had it before the gear swap.

The ABS sensors are on the diff. Maybe something worked loose after the install. It is easy enough to check. Take a business card with you when under the car. The gap between the sensor and the star wheel is about the width of a business card. That is how I set mine after installing the Harropp cover.

Check your tail lights, if one is burned out you will get a traction control fault. This happened to me when I did LED bulbs in the tail lights.

How is the performance with the gears? I have a 6-speed with 4.11's, basically stock power train. The difference on the street with the gear is amazing. I am very happy I did it.

With the power you are putting down I am sure you will have some traction issues. :-)

Let us know what you think of the throttle response with the new gear.
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Old 09-30-2018, 01:19 AM   #22
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How are you liking the 3.91s? Is your car A4 or M6?
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