3.42 rear end?
Thread Starter
Intermediate
Joined: Jun 2003
Posts: 48
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From: Glendale Ca.
3.42 rear end?
I own a C5 with automatic transmission. It has 3.15 gears. If I install a 3.42 rear end, will it dramatically give me more acceleration on the bottom end? Does anyone know how this change will affect the top end? At 75 mph, what will the tach read?
Thanks...;
Thanks...;
Le Mans Master
Joined: Oct 2001
Posts: 5,577
Likes: 3
From: Southern Maryland Maryland
Originally Posted by 2k1 VET
I own a C5 with automatic transmission. It has 3.15 gears. If I install a 3.42 rear end, will it dramatically give me more acceleration on the bottom end? Does anyone know how this change will affect the top end? At 75 mph, what will the tach read?
Thanks...;
Thanks...;
Racer
Joined: Mar 2006
Posts: 464
Likes: 0
From: silverdale washington
I dont think you would be happy w/ a 3.42, Id go at least 3.73.
Anyways i was going to figure it out but i cant find the a4 gearing specs, you can take new gear divided by old gear and get a ratio 3.73/3.15 = 1.184 now multiple that by your rpm and that how many rpm for the same mph with new gearing.
Anyways i was going to figure it out but i cant find the a4 gearing specs, you can take new gear divided by old gear and get a ratio 3.73/3.15 = 1.184 now multiple that by your rpm and that how many rpm for the same mph with new gearing.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
3.15 to 3.42 is the least amount of change one can make... 8.6%
but it all depends on your goals. I did that exact same change and am happy where it took me. But your goals may be different.
but it all depends on your goals. I did that exact same change and am happy where it took me. But your goals may be different.
Drifting
Joined: Mar 2003
Posts: 1,398
Likes: 1
From: Kingsport TN
I have 3.42 and in OD I recall I was running about 2400 on my tach if that helps. I have a blower so I'm set as far as my rear gears, however, if I didn't have a blower, I'd definitely want the 3.73 rear.
Racer
Joined: Jun 2004
Posts: 433
Likes: 0
From: Brookfield WI
I'm at 2,450 rpm (A4 w/3.42) at 75 mph.
When I just had the cam (367 rwph, 356 rwtq) the gears did not seem to do enough (I also started with 3.15). After adding heads and a Fast 90 (now at 423 rwhp and 391 rwtq) I'm glad that I didn't go any lower.
My tires will break free with ease up to just under 100 mph (things you find out by accident - not by trying) without downshifting. If you get a downshift it definitely breaks loose. And, trying to launch without spinning my tires leaves 40' - 60' posi marks. BTW, I have Z06 rims and F1 Supercar tires, and a stock TC.
With a stock or barely modified engine you might want to consider the 3.73 gears (unless you do a lot of highway driving - in which case the higher engine rpm might bug you a bit). The more HP you have the less you will appreciate lower gears. Just my $0.02.
Chip
When I just had the cam (367 rwph, 356 rwtq) the gears did not seem to do enough (I also started with 3.15). After adding heads and a Fast 90 (now at 423 rwhp and 391 rwtq) I'm glad that I didn't go any lower.
My tires will break free with ease up to just under 100 mph (things you find out by accident - not by trying) without downshifting. If you get a downshift it definitely breaks loose. And, trying to launch without spinning my tires leaves 40' - 60' posi marks. BTW, I have Z06 rims and F1 Supercar tires, and a stock TC.
With a stock or barely modified engine you might want to consider the 3.73 gears (unless you do a lot of highway driving - in which case the higher engine rpm might bug you a bit). The more HP you have the less you will appreciate lower gears. Just my $0.02.
Chip
Team Owner
Joined: May 2005
Posts: 23,682
Likes: 9
From: Flagstaff Az.
3:42s
You will get many different answers from different members. I went from 3:15s to 3:42s and a 3500 stall convertor. I personally would not go to 3:73s or lower as I drive a fair amount of highway miles. The change in rpms was very noticable to me. You might consider the hi-stall convertor because the labor isn't that much more with the rear end dropped. You can get $400-500 for your old 3:15s(depending on the miles) as they are sought by people who have the 2:72s in their a4 cars.
Le Mans Master
Joined: Aug 2003
Posts: 9,298
Likes: 4
From: American Canyon Lethal Injection
A4 C5 I went from the 2.72 to 3.15 to 3.42s. If I had went right to the 3.42 I would have appreciated the 3.42s more, but I'm happy with the 3.42s. I can feel the improvement when in D3, it's a faster launch. In D at 75/80 MPH I'm doing 2300 to 2500 RPMs. The best feeling and improvement is going from 70 to 100+ MPH. it happens in a flash
Last edited by SLPRC5; Oct 16, 2006 at 10:34 PM.
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Safety Car
Joined: Jul 2002
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From: Fishing Somewhere Cold
St. Jude Donor '11-'12-'13, '15
I went from 2.73 to 3.42 and added a sy3500....it was dramatic for me!!
However like most have stated above, not sure if it is worth it starting with the 3.15's. Good luck with your decision
However like most have stated above, not sure if it is worth it starting with the 3.15's. Good luck with your decision
Burning Brakes
Joined: Feb 2005
Posts: 752
Likes: 1
From: Tulsa OK
I went from 3:15 rear to a 3:42.
Noticeable change in acceleration - car pulls much stronger. It will break lose from 1st to 2nd and 2nd to 3rd at WOT. Rpms at 75 are between 2200 and 2400 in overdrive. Mileage is about the same.
Plan to do a stall next. I recommend you do the rear and stall at the same time. I was told to do it that way but didn't listen and now I'm going to pay the same labor as the rear install all over again.
Noticeable change in acceleration - car pulls much stronger. It will break lose from 1st to 2nd and 2nd to 3rd at WOT. Rpms at 75 are between 2200 and 2400 in overdrive. Mileage is about the same.
Plan to do a stall next. I recommend you do the rear and stall at the same time. I was told to do it that way but didn't listen and now I'm going to pay the same labor as the rear install all over again.
Team Owner
Joined: Apr 2001
Posts: 54,204
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From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by Whiteonrice
At 70 mph in third with an A4 (1:1) no OD or 4th in a MN6 the tach will tell what rearend you have approximately. 2.73 = 2,730 3.42 = 3,420 etc.
Rick
Rick
Race Director
Joined: Dec 2003
Posts: 10,455
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From: MI
Originally Posted by Whiteonrice
At 70 mph in third with an A4 (1:1) no OD or 4th in a MN6 the tach will tell what rearend you have approximately. 2.73 = 2,730 3.42 = 3,420 etc.
Rick
Rick
Team Owner
Joined: Apr 2001
Posts: 54,204
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From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by TYSON1997
it would drop 433 rpm w/ 3.15 and 399rpm w. 3.42
anyways... take any 2.73 RPM in any tranny gear, and multiply it by 1.15 to get the 3.15 rear ratio'd rpm; or by 1.25 to get the 3.42 equivalent.
Last edited by Mike Mercury; Oct 20, 2006 at 12:07 PM.