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    Mar 30, 2007 6:05:37 PM

    andrea
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    andrea
    Loc: Italy, Pordenone , Italy
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    Shorter gear ratios option for 997 GT3???

    On the current italian issue of Autocar there is the test of 997 gt3.speaking about the gearbox they wrote that the gear's ratios are too much long and also porsche noted it because now offers a set of shorter gear ratios.
    It's an exclusive option or what????
    with closer gears I suppose also acceleration times are different (better)

    Mar 30, 2007 7:06:43 PM

    Grant
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    Loc: Denver, CO , United States
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    Reply to: andrea

    Re: Shorter gear ratios option for 997 GT3???

    GT3's have always had the option (after purchase) of changing the individual gear ratios as well as the ring & pinion gears. It is very expensive, but makes a huge difference wherever top speed or quiet high-speed cruising are not required (especially good on any track with top speeds under 150mph)

    Mar 30, 2007 7:30:06 PM

    Mithras
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    Loc: Toronto, Canada , Canada
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    Reply to: Grant

    Re: Shorter gear ratios option for 997 GT3???

    Gears are the most useful and noticable "horsepower" you can buy for your car.

    Very few of us need a car that is geared for 190+mph and putting in lower gears so that you actually pull a top speed of around 165 mhp in 6th (as opposed to in 5th like many 6 speed cars) would absolutley transform a GT3.

    Looking at the gear charts 1st is good for 50mph, 2nd 84mph, 3rd 116mph, 4th 148, 5th 180 and theoretically 6th could do 207mph. 6th is an overdrive at 0.92:1

    Putting a Cup Car/RSR Ring & Pinion (8/32 aka 4:1 versus the stock 3.44:1) would make for a much faster car in all conditions (except top speed, but it would get up to its top speed of 178 much faster...)

    In fact, I would say that this is the fastest, easiest and maybe one of the cheapest ways to make your GT3 significantly faster (especially seat of the pants faster).

    Doing that would mean that in 6th cruising on the highway at 80mph you would be at around 3800 rpm in 6th.

    Mar 30, 2007 7:39:18 PM

    Grant
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    Grant
    Loc: Denver, CO , United States
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    Reply to: Mithras

    Re: Shorter gear ratios option for 997 GT3???

    Mithras is right and I would go on to say that beyond R&P change, changing the individual gear ratios to be lower and closer together is an even bigger improvement.

    Just changing the R&P will improve acceleration, but it does not change the rpm drops on upshifts. Creating a custom gearset with closer ratios allows the engine to make more power more of the time - a huge benefit and it won't make 1st gear too low to be usable as an R&P change can sometimes do on its own...

    Mar 30, 2007 9:52:13 PM

    PandaMan
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    PandaMan
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    Reply to: Grant

    Re: Shorter gear ratios option for 997 GT3???

    so how much would it cost?

    Mar 30, 2007 10:12:08 PM

    Grant
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    Grant
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    Reply to: PandaMan

    Re: Shorter gear ratios option for 997 GT3???

    Quote:
    PandaMan said:
    so how much would it cost?


    I can't remember exactly, but, with labor, in the neighborhood of $5k for just R&P, maybe $7k for a new gearset (change top 4 gears) and around $12k for both. Just a ballpark...

    Of course, while you're in there, you might as well upgrade the LSD to a Porsche Motorsports or Guard Transmission unit, which are both signifantly better than stock...

    Mar 31, 2007 1:19:57 AM

    Mithras
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    Mithras
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    Reply to: Grant

    Re: Shorter gear ratios option for 997 GT3???

    I don't have the gear charts in front of me, but with stock gears and the Cup/RSR R&P you're looking at a top speed of about 42mph in 1st, so you still have usable gears.

    Changing the R&P does in essence make all of your gears shorter and closer but not to the degree or correctness that changing each of them out does. But at some point you begin to split hairs...

    The big difference is with the stock gears and R&P you have between 32-37mph between each gear. With the Cup/RSR R&P you have about 25 mph between each gear.

    Really what you want is when you hit redline and shift it takes the rpm's in the next gear down to the beginning of the peak power curve. That's how a little engine with the right gears can WALK away from a big nhp car with gears made for economy.

    Mar 31, 2007 6:41:38 AM

    Grant
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    Grant
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    Reply to: Mithras

    Re: Shorter gear ratios option for 997 GT3???

    Quote:
    Mithras said:Changing the R&P does in essence make all of your gears shorter and closer but not to the degree or correctness that changing each of them out does. But at some point you begin to split hairs...


    No, unless you change individual ratios they will not be closer (just lower with lower R&P). You will still have identical rev drops between gears as you do stock. I was confused about this until I used a software program to draw some graphs - I can send you one if you're curious...
     
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