Changing From 2:73 to 3:42
Thread Starter
Racer
Joined: May 2006
Posts: 322
Likes: 1
From: Pembroke Ont.
Changing From 2:73 to 3:42
I will be changing my 02 -A4 to 3:42,S out of an Z06. I am told that the speedo will be fine, but I have to reprogram my shift points.I really don't understand this. Dosen't the car shifts at the same RPM, only sooner with the lower gears? Don't understand!!
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
NO !!!
but I have to reprogram my shift points.I really don't understand this. Dosen't the car shifts at the same RPM, only sooner with the lower gears? Don't understand!!
I don't have the specific numbers in front of me right now, but for discussions sake - say with your 2.73 the 1-2 WOT shift occrrred at 58mph at 6000rpm.
With the 3.42's you will need the PCM to command the 1-2 WOT shift at a lower MPH... lets say 47mph (or whatever the new value is) which is now where you'll be at 6000rpm.
If you don't reprog, the PCM tries to hold the A4 in first gear - in attempts to reach 60mph. But long before you get there you'll of reached 6200rpm and the rev limiter will kick in. You will never get a 1-2 WOT shift
Also; there's the needed alterations of the TCC slip table - done so you won't get the P1870 code thrown and the tranny placed in the limp mode.
.
Last edited by Mike Mercury; Mar 11, 2008 at 10:34 PM.
Thread Starter
Racer
Joined: May 2006
Posts: 322
Likes: 1
From: Pembroke Ont.
Makes sense now! I'm sure the guy putting them in would know this but I couldn't understand the RPM thing, Now I know. From what I have been hearing on this swap I will be very pleased....Thanks Guys
Thread Starter
Racer
Joined: May 2006
Posts: 322
Likes: 1
From: Pembroke Ont.
Drifting
Joined: Oct 2000
Posts: 1,396
Likes: 0
From: Sacramento CA
A question for you
What are you going to do with your old gears? I am looking at changing out my 3:42's in my Open Road TT racecar. This is running at high speeds for distance so getting out of the hole is not a big deal. I have 3:15's in my vert that I am looking at useing, but if I could find a great deal on 2:73's I might go that way.
Thanks,
Jeffy'
Thanks,
Jeffy'
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Melting Slicks
Joined: Feb 2002
Posts: 2,613
Likes: 1
From: Winston Salem NC
NO !!!
WOT automatic shifting has to meet two criteria, RPM and MPH values stored in a table within the PCM computer. After an A4 gear swap; the WOT RPM shift value stays the same, but the WOT MPH shift value in the table is no longer accurate.
I don't have the specific numbers in front of me right now, but for discussions sake - say with your 2.73 the 1-2 WOT shift occrrred at 58mph at 6000rpm.
With the 3.42's you will need the PCM to command the 1-2 WOT shift at a lower MPH... lets say 47mph (or whatever the new value is) which is now where you'll be at 6000rpm.
If you don't reprog, the PCM tries to hold the A4 in first gear - in attempts to reach 60mph. But long before you get there you'll of reached 6200rpm and the rev limiter will kick in. You will never get a 1-2 WOT shift
Also; there's the needed alterations of the TCC slip table - done so you won't get the P1870 code thrown and the tranny placed in the limp mode.
.
WOT automatic shifting has to meet two criteria, RPM and MPH values stored in a table within the PCM computer. After an A4 gear swap; the WOT RPM shift value stays the same, but the WOT MPH shift value in the table is no longer accurate.
I don't have the specific numbers in front of me right now, but for discussions sake - say with your 2.73 the 1-2 WOT shift occrrred at 58mph at 6000rpm.
With the 3.42's you will need the PCM to command the 1-2 WOT shift at a lower MPH... lets say 47mph (or whatever the new value is) which is now where you'll be at 6000rpm.
If you don't reprog, the PCM tries to hold the A4 in first gear - in attempts to reach 60mph. But long before you get there you'll of reached 6200rpm and the rev limiter will kick in. You will never get a 1-2 WOT shift
Also; there's the needed alterations of the TCC slip table - done so you won't get the P1870 code thrown and the tranny placed in the limp mode.
.
You didn't mention needing to change the gear settings. I know you have before.
from GM
TC P1870 Transmission Component SlippingRange
Gear Shift Solenoid TCC Solenoid TCC PWM Solenoid 2-4 Band Forward Clutch 3-4 Clutch Torque Converter Clutch
1-2 2-3
Overdrive 4th ON OFF ON 90% (ON) Applied Applied Applied Applied
Circuit Description
The Powertrain Control Module (PCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +30 RPM. The table above indicates solenoid states and transmission components that apply, during 4th gear, with the TCC commanded ON.
Le Mans Master
Joined: May 2006
Posts: 7,885
Likes: 259
From: Hillsboro OR
Just an FYI, When I did the swap, I used the HPTuners programer. When I entered the new gear ratio as 3:42, the HP Tuner set automatically changed the shift points. I still massaged my shift points and shift times to be a little more aggressive.
