3.91 gears - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

rdavis · 09-21-2016, 10:13 AM

I have an opportunity to purchase a 3.91 diff. for a very good price. I would like to hear impressions from those who have gone with 3.91's on a manual trans SS. Thanks

mrvenicess · 09-21-2016, 10:16 AM

I had them on my 2010 SS, best mod I did.

rdavis · 09-21-2016, 10:26 AM

Any negative difference at highway speeds? According to the calculators at 80 mph my rpms will be about 250 higher. Seems like nothing to be concerned about. But I do some traveling from colorado to texas. Still want to be able to comfortably cruise at 80. Thanks

SquawkVFR · 09-21-2016, 10:44 AM

You'd get a lot more better information quicker if you did an advanced search for threads (posts only) under "3:91".

Having said that, it's a great mod the highway cruise is fine and my impression is "VROOOOOOOOOOOOOOOOOM".

olblue75 · 09-21-2016, 12:03 PM

I put them in my 2010 SS M6 and as stated above its the best mod to date, highway speeds are not that bad I travel 30 minutes a day on the interstate at 80-85 and 250 RPMs you are not going to notice. Now if you have a M6 car first gear is a little quick/deep so be prepared to shift quickly if your really on it. Also you'll have to get your speedo re-calibrated or you'll be putting false mileage on it. All in all a good mod if your getting the diff cheap, just remember to drain and flush and put in fresh fluid.

acammer · 09-21-2016, 12:32 PM

Subscribed to hear additional opinions - strongly considering this for a spring modification.

Quote:

Originally Posted by olblue75

... Now if you have a M6 car first gear is a little quick/deep so be prepared to shift quickly if your really on it...

From my experience at the drag strip I think a shorter first gear will benefit the car. When launching I find there is a fine line between too much rpm resulting in wheel spin, and too little rpm resulting in a bog. The solution is working the clutch harder - however a shorter first gear will help leave with a little less RPM and clutch, letting the car hook, and then jump right up into the power. Typically I don't have problems with grip once the car is out 30' - it's just initially getting rolling that it really is a fight between the spin and the bog.

It'll improve RPM at the traps, but maybe hurt mph. Currently I shift to 4th at around 107mph, maybe 1 second before the beams and finish at around 4500rpm. Going to a 3.91 should be me into 4th by 100mph and through the traps at around 5100rpm. Hard to say if that's going to help or hurt trap speed as you'll actually spend more time at the big end with less rpm (into 4th sooner), and thus less hp. The car will crush the 1/8th mile traps on a 3.91 though, that's for sure.

Royal Tiger · 09-21-2016, 02:28 PM

It's my next mod. I can't wait!

frankwjr · 09-21-2016, 02:54 PM

Too bad can't get a group buy for something like this...it's my next mod too...including replacing the stock center section wit tru trak...JPE bearing caps...LPW cover...

CamaroFred · 09-21-2016, 04:40 PM

Quote:

Originally Posted by acammer

Subscribed to hear additional opinions - strongly considering this for a spring modification.

...

It'll improve RPM at the traps, but maybe hurt mph. Currently I shift to 4th at around 107mph, maybe 1 second before the beams and finish at around 4500rpm. Going to a 3.91 should be me into 4th by 100mph and through the traps at around 5100rpm. Hard to say if that's going to help or hurt trap speed as you'll actually spend more time at the big end with less rpm (into 4th sooner), and thus less hp. The car will crush the 1/8th mile traps on a 3.91 though, that's for sure.

If you use 275/40 rears with your 3.45s 3rd will top ~113. Maybe you wouldn't need to hit 4th.

acammer · 09-21-2016, 06:27 PM

Quote:

Originally Posted by CamaroFred

If you use 275/40 rears with your 3.45s 3rd will top ~113. Maybe you wouldn't need to hit 4th.

I didn't experiment with that, but I agree by the math I should be able to finish in third. It wouldn't surprise me to learn there is some error in the stock tach - by that 107mph is 6500rpm in third. Now that I've got my 12.xx slip in hand I can start experimenting some more.

rdavis · 09-21-2016, 07:04 PM

I'm used to a short 1st gear. My 13 5.0 had a 3.66 first gear with a 3.73 rear. 1st didn't last long. Thanks for all the replies.

SquawkVFR · 09-21-2016, 10:08 PM

If you get dealer install (gm parts) you get a one year warranty.

acammer · 09-22-2016, 08:39 AM

Quote:

Originally Posted by rdavis

I'm used to a short 1st gear. My 13 5.0 had a 3.66 first gear with a 3.73 rear. 1st didn't last long. Thanks for all the replies.

Bet that moved off the line quick!

rdavis · 09-25-2016, 04:47 PM

Ok update: This is the gear that should have come in these cars. Feels so much more peppy. Starting to feel like my 5.0 (sorry) Take offs are much easier. Highway is still a piece of cake.2000rpm is still 75mph. All in all very happy. Only downside is that I traded a friend complete differentials & he has urethane bushings in this one. Kind of noisy. Gears themselves are quiet. This might sound stupid but can you get replacement housing bushings from GM? I dont drag race so the factory rubber bushings are fine with me. I just don't like the noise the poly ones transmit.

09-21-2016, 10:13 AM	#1
rdavis Drives: 2012 SS Join Date: Feb 2016 Location: Lubbock Texas Posts: 121	3.91 gears I have an opportunity to purchase a 3.91 diff. for a very good price. I would like to hear impressions from those who have gone with 3.91's on a manual trans SS. Thanks

09-21-2016, 12:03 PM	#5
olblue75 Drives: 2010 2SS/RS Join Date: Dec 2009 Location: Clarksville Tennesse. Posts: 6,064	I put them in my 2010 SS M6 and as stated above its the best mod to date, highway speeds are not that bad I travel 30 minutes a day on the interstate at 80-85 and 250 RPMs you are not going to notice. Now if you have a M6 car first gear is a little quick/deep so be prepared to shift quickly if your really on it. Also you'll have to get your speedo re-calibrated or you'll be putting false mileage on it. All in all a good mod if your getting the diff cheap, just remember to drain and flush and put in fresh fluid. __________________ Orange Krush II 1LE Front sway bar, Splitter, shocks and struts, Z28 dual mode mufflers, Intake, UCA Bushings, and Toresen 3.91 Diff. 1 piece DSS Drive Shaft, ZL1/C7 Calipers, and 32mm JPSS Rear Bar. ASC race spec splitter and wicker. 6th Gen M017 Wheels. Stainless Works 1 7/8 LTs. DSE and PAFDT Suspension components.

09-21-2016, 02:54 PM	#8
frankwjr Drives: 2010 SS 2SS M6 Join Date: Aug 2016 Location: Smithsburg, Md. Posts: 2,445	Too bad can't get a group buy for something like this...it's my next mod too...including replacing the stock center section wit tru trak...JPE bearing caps...LPW cover... __________________ 2010 SS 2SS M6 - Tune by RDP dynoSteve!(Woot) - Daily Driver - *150K!* - All work by me...

09-21-2016, 10:16 AM	#2
mrvenicess Drives: 2013 CRT ZL1 auto Join Date: May 2010 Location: Venice Fl Posts: 1,443 View My Garage	I had them on my 2010 SS, best mod I did.

09-21-2016, 10:26 AM	#3
rdavis Drives: 2012 SS Join Date: Feb 2016 Location: Lubbock Texas Posts: 121	Any negative difference at highway speeds? According to the calculators at 80 mph my rpms will be about 250 higher. Seems like nothing to be concerned about. But I do some traveling from colorado to texas. Still want to be able to comfortably cruise at 80. Thanks

09-21-2016, 10:44 AM	#4
SquawkVFR Account Suspended Drives: 2010 Camaro Join Date: May 2014 Location: Alabama Posts: 1,971	You'd get a lot more better information quicker if you did an advanced search for threads (posts only) under "3:91". Having said that, it's a great mod the highway cruise is fine and my impression is "VROOOOOOOOOOOOOOOOOM".

09-21-2016, 02:28 PM	#7
Royal Tiger Account Suspended Drives: 2013 2SS/RS Convertible Join Date: Apr 2016 Location: Lehigh Valley, PA Posts: 3,873	It's my next mod. I can't wait!

09-21-2016, 07:04 PM	#11
rdavis Drives: 2012 SS Join Date: Feb 2016 Location: Lubbock Texas Posts: 121	I'm used to a short 1st gear. My 13 5.0 had a 3.66 first gear with a 3.73 rear. 1st didn't last long. Thanks for all the replies.

09-21-2016, 10:08 PM	#12
SquawkVFR Account Suspended Drives: 2010 Camaro Join Date: May 2014 Location: Alabama Posts: 1,971	If you get dealer install (gm parts) you get a one year warranty.

09-25-2016, 04:47 PM	#14
rdavis Drives: 2012 SS Join Date: Feb 2016 Location: Lubbock Texas Posts: 121	Ok update: This is the gear that should have come in these cars. Feels so much more peppy. Starting to feel like my 5.0 (sorry) Take offs are much easier. Highway is still a piece of cake.2000rpm is still 75mph. All in all very happy. Only downside is that I traded a friend complete differentials & he has urethane bushings in this one. Kind of noisy. Gears themselves are quiet. This might sound stupid but can you get replacement housing bushings from GM? I dont drag race so the factory rubber bushings are fine with me. I just don't like the noise the poly ones transmit.