Question on Differentials | FerrariChat

Question on Differentials

Discussion in 'General Automotive Discussion' started by Auraraptor, Nov 8, 2004.

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  1. Auraraptor

    Auraraptor F1 World Champ
    Lifetime Rossa Owner

    Sep 25, 2002
    13,221
    MO
    #1 Auraraptor, Nov 8, 2004
    I wanted to up the final drive in my BMW.

    Another individual has installed a 3.15 in his car (from a stock 2.92). He noted the following change:

    0-60: 6.466s
    1/4 mile: 14.254 at 101mph

    after 3.15 differential:

    0-60: 6.001s
    1/4 mile: 14.699sec at 95mph

    He had his car checked out and everything is running ok. I was just wondering, why did he see the loss in the 1/4?

    It was checked to see if there was an additional shift now that the final drive was lower and this was not the case.

    Is this normal whenever one ups the final drive? I wonder since I want to up the final drive in my car from the stock 2.82 to 3.15 or a 3.46.
    Thanks!
     
  2. Hubert

    Hubert F1 Rookie

    Jan 3, 2002
    2,642
    The Left Coast
    #2 Hubert, Nov 9, 2004
    I'm no 1/4 mile expert, but what were his 60 foot and reaction times? Without knowing that those two numbers were the same b/w runs, it's moot to ask "what happened?"
     
  3. Auraraptor

    Auraraptor F1 World Champ
    Lifetime Rossa Owner

    Sep 25, 2002
    13,221
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    #3 Auraraptor, Nov 9, 2004
    I shall ask. Thanks for the reply!
     
  4. Hubert

    Hubert F1 Rookie

    Jan 3, 2002
    2,642
    The Left Coast
    #4 Hubert, Nov 9, 2004
    No problem. Looking over your post again, your friends relusts are what I'd expect; quicker accel overall - he dropped 1/2 a second off his 0-60 time. That's a marked change.
     
  5. Auraraptor

    Auraraptor F1 World Champ
    Lifetime Rossa Owner

    Sep 25, 2002
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    #5 Auraraptor, Nov 9, 2004
    He said it is average of 3 runs using a properly calibrated GTech Competition.

    Also, the drop in his 60 time was what I was expecting, but I was also expecting a similar drop in his 1/4 mile. Yet the 1/4 increased, which had me baffled.

    In a nutshell, if I do swap my differential and increase my final drive to a 3.15 from a stock 2.82, would I, assuming there is no additional shifts now needed, also see an increase in my 1/4 mile time?
     
  6. TimN88

    TimN88 F1 Veteran

    Jun 12, 2001
    5,045
    Northeast
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    Tim
    #6 TimN88, Nov 9, 2004
    what might have happened is that he now has to shift to the next higher gear, which he otherwise would not shift into using the taller gears. This is all i can think of, however this really shouldnt slow him down.
    edit- ok i just saw where you said that was not the case. I would begin to question the g-tech meter. Also, were the tests performed on the same road? The latter test might have a slight uphil that isnt reached till after 60mph.
     
  7. Hubert

    Hubert F1 Rookie

    Jan 3, 2002
    2,642
    The Left Coast
    #7 Hubert, Nov 9, 2004
    Oh. GTECH pro? Dunno man. I think that you'd need to run 'er at the strip as to get an accurate base line - too many variables when self administring. A shorter FD will pull you through the grears quicker - you shuld accelerate quicker out of the hole and off a corner, but 1/4 times may drop b/c you'll be rowing through the gears and top speed will take a drop too.
    I wouldn't (can't) attach much weight to your friends "data" as it seems ambigous.
     
  8. Redline Drift

    Redline Drift Rookie

    Dec 10, 2003
    46
    #8 Redline Drift, Nov 9, 2004
    Yeah, an extra shift is what it looks like is cutting the time.
     

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