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Old 11-04-2009, 06:57 AM   #1
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Differential Ratio

Has anyone ever considered altering the final drive ratio on their Boxster?

Certainly with the S model and it's tall 6th gear, I am sure shortening the final drive would not hurt top end speed. It would help the car feel a little more responsive around town too.

I have given up trying to get more power out of my car, nothing bolt-on is really significant for a low cost. I am keeping clear of switching to the single mass FW due to the issues discussed in depth by Jake Raby. It seems lowering final drive could be the least expensive and safest way to get more poke out of our cars.

I would like to hear others thoughts on this and if anyone knows where we could buy a differential with shorter gearing to fit our cars.
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Old 11-04-2009, 07:21 AM   #2
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An easy way to do this is to simply run lower profile tires. Several drivers run 245/40/17 tires to lower the effective final ratio. 285/30/18 works also.
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Old 11-04-2009, 07:22 AM   #3
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I've seen advertisements for different gears in the back of Panorama magazine, so there are companies doing it. Your speedometer and odometer will be inaccurate, though, unless you have your ECU reflashed to correct the speedometer multiplier in the ECU. (Been there, done that with three different Camaros.)

You also will need to find a VERY experienced gear installer to set the pinion depth correctly, or you will get a horrible gear howl at highway speeds. (Again, been there, done that.)
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Old 11-04-2009, 08:07 AM   #4
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I believe Guard makes gearsets for at least the 6-speed boxes, not sure on the 5-speed. Don't think you want to ask about the cost And then, as mentioned previously, you need to find a good shop to build the box for you (as if you're going that far, you may as well replace syncros and bearings, and if it were me, add an LSD).
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Old 11-04-2009, 08:09 AM   #5
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I have toyed with the idea - gboxweb.com.
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Old 11-04-2009, 09:32 AM   #6
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Quote:
Originally Posted by Cloudsurfer
I believe Guard makes gearsets for at least the 6-speed boxes, not sure on the 5-speed. Don't think you want to ask about the cost And then, as mentioned previously, you need to find a good shop to build the box for you (as if you're going that far, you may as well replace syncros and bearings, and if it were me, add an LSD).

This sounds like the best way to me, going from 265/35/18 to 285/30/18 rear tire makes noticeable improvement in acceleration but car resists rotating in turns
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Old 11-04-2009, 11:24 AM   #7
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I have short gears and a 7:31 RP in the old 911...cost is not for the faint of heart.
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Old 11-04-2009, 11:38 AM   #8
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I see used Boxster R&P gears on E-bay alot I assume from Spec racers. I think there are 3 ratios to choose from
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Old 11-04-2009, 07:11 PM   #9
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Thanks everyone.

Sorry I didn't clarify, I have the S with 6 speed, should have mentioned that. So much is the same with the 2 cars that I rarely differentiate, but of course the drivetrain is different.

Good point running lower profile tyres, unfortunately I replaced them about 3 weeks ago with the stock 265/35 18 rear and 225/45 18 front.

I was hoping to find an entire differential geared shorter to just exchange with the old one. If it came in a clutch-type lsd even better. I agree that getting in there and changing gears will be very expensive and risky if it is not done correctly.

The way I see it I am not racing in a Cup car or the likes where the ratio needs to be perfectly suited to a track, just something a little shorter to give the car some more pep around town.

I will keep googling and see what I find. Will post any worthwhile results.
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Old 11-04-2009, 07:48 PM   #10
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Unless something has changed in the last year Guard does not make gears for the 6 speed. The only place I have found is California Motorsports that has a gear set for the 6 speed. They have the ability to install them as well.

Just my $.02

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