rear gear upgrade for a4
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Joined: Oct 2004
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rear gear upgrade for a4
Hi i have a 01 c4 a4 with 3.15's, I would like to upgrade to a steeper gear like a 3.42 or a 3.90 but im worried about loosing top end, i know the 3.42 will be ok for top end but the 3.90 is pushin it with an a4, I still want to be able to hit 175 if a race turns into a top end battle, I know im going to get flamed for top end racing but you never know when ya need to keep going until someone runs out of steam gearing/drag whatever. whats the top end for a auto with 3.90s or even the 4.10s thanks guys
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
Your car is not top end limited because of gear, its top end limited because of aerodynamics. You can only overcome this with more power.
Team Owner
Joined: Apr 2001
Posts: 26,794
Likes: 614
From: Elmhurst, IL (West Suburb of Chicago) & Home of MEGA Horsepower
St. Jude Donor '06
YEah i agree 1000%. Go at least 3.73 and better yet the best performing A4s are running 3.90s. If you only jump up to 3.42 its not worth as the bang for the buck is not cost effective. If you really want to wake that biatch up go with 4.10s as more than a few A4 guys have now done and the LOVE IT and it still won't effect your top end and with your overdrive tranny you will be fine not spinning to high. 3.90s though would be your best all around bet if you want the best 0 to 110 mph although 3.73s would be the most practical gear to upgrade to if you ask most folks here, if this is a daily driver for ya! 
Instructor
Joined: Sep 2003
Posts: 130
Likes: 1
From: Florida Treasure Coast
I have 3.73s and have plenty of top end 
I'll have even more when I add heads in the spring 
Also you should get the gears with a hardened output shaft if you plan on driving aggressively. The bigger you go the easier it is to break a tooth 
I'll have even more when I add heads in the spring Also you should get the gears with a hardened output shaft if you plan on driving aggressively. The bigger you go the easier it is to break a tooth
Last edited by FNFAST; Oct 22, 2004 at 10:47 PM.
Burning Brakes
Joined: Nov 2003
Posts: 790
Likes: 7
From: Denton TX
Originally Posted by 01vette87GN
Hi i have a 01 c4 a4 with 3.15's, I would like to upgrade to a steeper gear like a 3.42 or a 3.90 but im worried about loosing top end, i know the 3.42 will be ok for top end but the 3.90 is pushin it with an a4, I still want to be able to hit 175 if a race turns into a top end battle, I know im going to get flamed for top end racing but you never know when ya need to keep going until someone runs out of steam gearing/drag whatever. whats the top end for a auto with 3.90s or even the 4.10s thanks guys
Let me get this straight. You want to be able to street race? You want to be able to do 175 if the race gets tough?
Am I hearing you right?
Melting Slicks
Joined: Jun 2001
Posts: 3,123
Likes: 3
From: Orland Park Illinois
St. Jude Donor '06-'07
Originally Posted by 01vette87GN
Hi i have a 01 c4 a4 with 3.15's, I would like to upgrade to a steeper gear like a 3.42 or a 3.90 but im worried about loosing top end, i know the 3.42 will be ok for top end but the 3.90 is pushin it with an a4, I still want to be able to hit 175 if a race turns into a top end battle, I know im going to get flamed for top end racing but you never know when ya need to keep going until someone runs out of steam gearing/drag whatever. whats the top end for a auto with 3.90s or even the 4.10s thanks guys
I hope and pray you don't live anywhere near Illinois.....
Last edited by BiggieBoy; Oct 23, 2004 at 06:23 AM.
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Melting Slicks
Joined: Jun 2001
Posts: 2,743
Likes: 3
From: Davie Florida
Originally Posted by LeMansBlue04
Excuse me but....
Let me get this straight. You want to be able to street race? You want to be able to do 175 if the race gets tough?
Am I hearing you right?
Let me get this straight. You want to be able to street race? You want to be able to do 175 if the race gets tough?
Am I hearing you right?
In some states they put you in jail and take away your car if they catch you racing, or driving at very excessive speeds on the streets. I think 175 MPH qualifys as excessive speed on the streets.
Last edited by Mitch C; Oct 23, 2004 at 07:05 AM.
Pro
Joined: May 2004
Posts: 533
Likes: 47
From: Tucson, AZ
Yeah bro I race on the streets too but come on...Anything over brief bursts to 120 is ridiculously stupid and a huge ticket/jail time waiting to happen...I'm not on the whole "I'm an old guy with no more testosterone who feels superior to those reckless street racers" band wagon, because in all actuality I street race quite often, but just be smart about it because it can really get out of hand fast
Drifting
Joined: Sep 2002
Posts: 1,947
Likes: 0
From: Howell MI.
Originally Posted by 01vette87GN
Hi i have a 01 c4 a4 with 3.15's, I would like to upgrade to a steeper gear like a 3.42 or a 3.90 but im worried about loosing top end, i know the 3.42 will be ok for top end but the 3.90 is pushin it with an a4, I still want to be able to hit 175 if a race turns into a top end battle, I know im going to get flamed for top end racing but you never know when ya need to keep going until someone runs out of steam gearing/drag whatever. whats the top end for a auto with 3.90s or even the 4.10s thanks guys
3.73 Had the 3.15 and then 3.42 now 3.73
check out this site for speed and rpm with different gears
http://www.smokemup.com/auto_math/mph_range2.php
Team Owner
Joined: Apr 2001
Posts: 26,794
Likes: 614
From: Elmhurst, IL (West Suburb of Chicago) & Home of MEGA Horsepower
St. Jude Donor '06
That's a great price if that includes the whole rear end diff unit complete and already set up, ready to be swapped into a C5!!! 
Is that the case and one must provide a 3.15 or higher number core for that price? If there is an extra fee for the core, how much, as i have a friend in the market!
Is that the case and one must provide a 3.15 or higher number core for that price? If there is an extra fee for the core, how much, as i have a friend in the market!
Le Mans Master
Joined: Jun 2004
Posts: 7,155
Likes: 154
From: The Arid Sunny Desert
3.90's are awesome but traction is an issue. Unless you run drag radials or even slicks you will have to learn how to feather the gas just right to launch with any effectiveness. Also highway cruising is a bit noisier but you get used to it after awhile. 70 mph @ 2500 RPM, 75 mph @ 2700 RPM.........seems to go up 200 RPM for every 5 mph increase in speed. With tons of mods and loud aftermarket exhaust it is a bit much for the passengers but who really cares about the passengers right??
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I live in tampa florda, I am friends with our sherrif, wont have a problem with jail. =o) now the death thing is another thing, but at 3 am in the morning on I75 there are some areas that are open and you can see for a mile ahead of ya so top end is ok in some areas =o) yea its illegal, so..
