"tranny trick" debunked 2.0

Discussion in 'GT4 Tuning' started by nomis3613, Jul 17, 2010.

  1. oldmodelt

    oldmodelt

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  2. mafia_boy

    mafia_boy (Banned)

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    WARNING!! VERY LONG POST!!


    I'm quoting what the differential ratio would be, so that's the final ratio. If you meant using the same wheel speed via different gear/diff ratios then that's a bit different and makes all my testing redundant. However, after looking at your results, both of you have quicker times with the CF driveshaft using the tranny trick, just RJ's was a lot bigger difference.

    Now as I said before and you realised, the ability to achieve gearsets that are not normally achievable with just an autoset change is the tranny trick. I've been doing some testing for you guys on this front to show the differences in doing the trick to improve the acceleration & top speed of your car and also changing the dynamic of how it delivers it's power & torque.

    The following was done using a near new (52.3km old) 2004 Subaru WRX STi Spec-C w/oil change (252Kw, 343hp), running everything completely standard, using a TCS of 5 for consistency.

    I originally used the standard gearbox for a baseline at the Las Vegas 1/4 mile track. After several test runs, I found the best launch was around 3000-3500rpm so I used that as my baseline takeoff rpm. Afterwards I fitted the FC gearbox and ran that on default settings, and thirdly I did a quick tranny trick to show the difference for acceleration.

    The gearset on the default FC was:
    Autoset 12, 1st: 3.447, 2nd: 2.351, 3rd: 1.729, 4th: 1.333, 5th: 1.076, 6th: 0.911, Final: 3.900.

    Using the tranny trick which is adjusting the final ratio to 5.500, then going to autoset, you're able to change the gearbox to get a closer ratio gearbox than normally possible. So I moved the autoset up to 3, but you will notice that 1st is still lower than the 1st on the default FC, even though the autoset is earlier. I then went very close to the default of this autoset and adjusted it slightly to get these settings with a slightly tricked FC:
    Autoset 3, 1st: 3.000, 2nd: 2.150, 3rd: 1.650, 4th: 1.325, 5th: 1.100, 6th: 0.925, Final: 3.900

    The times were:
    Stock: 12.300
    FC Default: 12.254
    FC Trick: 12.127

    I then took each of them out for a Max Speed test at the Test Course with those settings and got the following speeds:
    Stock: 279.54km/h
    FC Default: 273.44km/h
    FC Trick: 271.65km/h

    Now I'm hearing you going, "But Mafs, you said it's supposed to improve both the speed and acceleration!" That's right, and I'm about to show you because the groundwork has already been laid out with the tranny trick, all it takes now is adjustment. So, knowing that we are 8km/h behind the stock gearbox in top speed, but already 0.173 infront over the 400m, what we want to do is maintain the acceleration advantage, but bring the speed up past the stock gearbox.

    This is the only pain about it, you have to bring the final ratio back to 5.500 before you readjust anything. After doing this, I changed the autoset to 4, but kept the same 1st gear I had as it was already set correctly for my launches and slightly adjusted the other gears. I wound up with this:
    Autoset 4, 1st: 3.000, 2nd: 2.075, 3rd: 1.575, 4th: 1.250, 5th: 1.025, 6th: 0.825, Final: 3.900.

    I then re-tested the car and got the following figures:
    400m: 12.123 (launched at 4000rpm)
    Top Speed: 280.77km/h

    So I've brought the car up to be 0.177 quicker over the 400m, and then continued that and been 1.23km/h faster at top speed. The motor was topping out at 7500rpm in 6th gear, couldn't get it going much faster than this with the aero drag and lack of power.

    Now, when all these changes in the gearbox occurred, it changed the way the car accelerated. With the taller first gear, the motor had to rev slightly higher (4000rpm vs 3000rpm) to keep it from bogging down at launch, but this also puts the motor right near it's peak torque and going up it's power curve at launch and with the turbo already boosting because you're revving higher, you end up launching a lot more violently than you would with the standard gearbox with the TCS struggling to hold the tyres from spinning.

    That's the tranny trick (one version of it anyway).
     
  3. nomis3613

    nomis3613 Premium

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    Great! Thanks for sharing your VERY LONG POST :)
    Actually, that is what I was testing...

    I don't think so. And it's very interesting anyway!

    Just wondering, are you able to get exactly the same times when launching from a specific rpm? I found (using the DS2 analogue stick) it was causing inconsistent times, so I tend to just bounce it off the limiter if I'm doing comparison testing these days.

    If only the dyno graph had a rev scale on it. Then we could geek it up with spreadsheets to calculate optimum gear ratios to stay in the power band. But maybe that would take away the fun of tuning...

    Yep. I've always thought (but never tested much 400m stuff) that higher launch revs = able to run taller 1st gear without bogging = able to run tighter gearing across the board = faster acceleration. (unless there is clutch slip in GT4? I've never looked into this)

    Thanks heaps! It's really impressive that after your first "tranny trick" setup you managed to increase top speed without sacrificing 400m time (in fact you actually improved it!!)
     
  4. mafia_boy

    mafia_boy (Banned)

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    I use the X button as it's pressure sensitive and gives me a better feedback when controlling the accelerator and therefore the rpm launch of any car. The analog stick doesn't allow you to do braking and throttle at the same time when circuit racing.

    I find that creating a gear graph that looks like a fan is opening is the best way of keeping the car in it's powerband. As you can see by the ratios I used in the 'trick' tests, I keep them close together to allow this to happen.

    There is a way you can slip the clutch in GT4 on launch through throttle control that allows you to launch at high rpm without smoking the tyres on takeoff. I've been able to do this with a lot of practice.

    It's because I set the first gearset to show the improvement in acceleration you can make without much effort, the next gearset was what you can do when you concentrate on both ends (acceleration and top speed). That gearset could be improved even further on the acceleration end, I know a 12.0xx is there with a slightly better 1st/2nd combination (say 2.900/2.000) and if you really really tried to maximise it I suppose you could possibly get an 11.9xx after much testing. That's while you're still maintaining that same top speed because 5th/6th would be untouched, as I only used 4 gears in the 400m.