Changing diff ratio for mph trap.
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Launching!
Joined: May 2003
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Changing diff ratio for mph trap. I am running 3.73 in a A4 we are running into the 1/4 at the end at the top of 3rd gear. This is at around 6100 and right on the change up,I could change the shift point put the power is dropping of at 6300.
I was considering putting in 4.11 gear which would mean seeing the trap at around 4800 rpm and right on our TQ peak and also give us scope for a better mph.
Are we on the right track with this or am I wrong.
I was considering putting in 4.11 gear which would mean seeing the trap at around 4800 rpm and right on our TQ peak and also give us scope for a better mph.
Are we on the right track with this or am I wrong.
I don't know too much about auto's, but I thought it was bad to shift into overdrive at the track.
What i've always been told is you should be shifting 200-300 rpm's past peak horsepower, so you should aim for that.
I think that extra shift would slow you down, it did for me in my M6 when I was shifting into 5th. I was losing .2-.3 at the track.
What i've always been told is you should be shifting 200-300 rpm's past peak horsepower, so you should aim for that.
I think that extra shift would slow you down, it did for me in my M6 when I was shifting into 5th. I was losing .2-.3 at the track.
TECH Senior Member
Joined: Nov 2001
Posts: 9,246
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From: Troy, AL
Sounds like it's just about right as it is. 
If anything I'd want to be crossing the line just after my HP peak (you're close enough that it would be of very little help to change anything gearingwise.) You certainly DON'T want to be crossing at your TQ peak (that has absolutely nothing to do with anything in regards to where you want to be crossing) nor do you want to be shifting into OD just before the finish line. NOT good.
If anything I'd want to be crossing the line just after my HP peak (you're close enough that it would be of very little help to change anything gearingwise.) You certainly DON'T want to be crossing at your TQ peak (that has absolutely nothing to do with anything in regards to where you want to be crossing) nor do you want to be shifting into OD just before the finish line. NOT good. TECH Senior Member
Joined: Nov 2001
Posts: 9,246
Likes: 3
From: Troy, AL
"That would mean if I was to want to stay in third and run a higher mph I would need to go to the other way to 3.46."
No, leave the gearing alone. If it wants to shift right at the line then put the gear selector in drive instead of overdrive....or you could raise the 3-4 shiftpoint.
No, leave the gearing alone. If it wants to shift right at the line then put the gear selector in drive instead of overdrive....or you could raise the 3-4 shiftpoint.
Exactly what Colonel said. I just went from 3.42 to 3.73 gears and my car was shifting 3 -4 at about the 1100' mark, so now I just run in D not OD and run that little extra rpm thru the traps.
