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Thread: Choosing the right ratios

  1. #1
    Join Date
    Feb 2019
    Location
    Warsaw
    Posts
    5
    My Cars
    E28, E39, EP3

    Choosing the right ratios

    Hi
    I'm in the process of sourcing parts for my E28 track car build, but the question is not model specific. I need advice on choosing the proper gearbox and diff ratios. If I decide only on the basis of calculator-supplied values then I am shure I would choose a good configuration on paper, that would be completely undriveable in the real world The gearbox will be a 6-speed Samsonas (multiple ratios in their specification, I have not decided seq or H-pattern, kinda heart vs wallet battle ) and the diff will be a custom billet aluminum racing unit, with ratios anywhere from 3.2 to 4.3. Is trying to mimic the ratios of an existing M model car a viable starting point? Do you know of any literature I could study that would help me choose a setup? Sadly I have a maximum of 1 month to make the decision and cannot read books which weight could kill a person if hit I'm a driver-investor and not an mechanic engineer sadly. The car will be a weekend driver. I do not plan on using it for drifting, or for any professional racing. I would appreciate any advice on the topic.

  2. #2
    Join Date
    Jul 2004
    Location
    Sid Knee
    Posts
    1,312
    My Cars
    325is, 96 M3 Euro
    will depend on the track (slowest corner speed and fastest straightaway speed) and also on the power curve (useable rpms). then you play around in excel plotting power vs road speed for each gear and see the shift points and try to maximise power at all possible speeds.
    BMW E30 325is M20B33 in the making....... ITB's, roller rockers and stroked to the hilt

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