Thom

3.1 R&P in a stock 6 speed trans, compared with 951 trans (AOR).

dand86951

Here is a chart showing the speed and mph in each gear for a 968 with stock gearing and a 3.4 r&p. This is with 335/30/18 rear tires which is a 25.9 in diameter.
MPH
Overall Gear Ratio by Gear
10.82 6.80 4.88 3.78 3.10 2.65
RPM 1st 2nd 3rd 4th 5th 6th
1000 7 11 16 20 25 29
1500 11 17 24 31 37 44
2000 14 23 32 41 50 58
2500 18 28 39 51 62 73
3000 21 34 47 61 75 87
3500 25 40 55 71 87 102
4000 28 45 63 82 99 117
4323 31 49 68 88 107 126
4962 35 56 78 101 123 145
5342 38 61 84 109 133 156
5655 40 64 89 115 141 165
5892 42 67 93 120 146 172
6200 44 70 98 127 154 181
6300 45 71 100 129 157 184
6400 46 73 101 131 159 186
6450 46 73 102 132 160 188
6600 47 75 104 135 164 192
6700 48 76 106 137 167 195
6800 48 77 107 139 169 198
6900 49 78 109 141 172 201
7200 51 82 114 147 179 210



I have underlined the mph at 6900rpm and show the rpm drop when shifting into the next gear assuming you are on the track and winding it up to 6900.

savvas944

i think the 911 GT3 RSR used in support of F1 RACES ,and Leman races use a 4.to 1 fd ratio ,as they use 670 mm rr tires,instead
of the 3.44. std GT2,GT3 and RS.
i noticed also on some tracks with long straights and fewer bends they use 680 mm rr tires
to compensate.
Is there a hint somewhere there like playing around with tires ,instead of fixed ratios final drives.
I have tried 670 tires on 11 inch x18 rears on my wide body and fit without any problem.
On the std body again 640-650 mm dia 250-270 slicks also fit on et 65 rr 10x18 rims.

333pg333

Interesting stuff guys. The more I look at it, the more I realise just how important the combination of all the components in the motor and drivetrain add up to the sum of the whole....if that isn't a bit too obvious. By that I mean that you can select what you think is the perfect gearbox, then decide on the gearing &/or RP and that's just one thing to consider. Then you need to match the turbo, cam, exhaust, headers, headwork, inlet, tb, i/c and pipes, fuel, ign and what else...tyre diameter yada yada yada. Because none of us are driving factory racecars with huge budgets and a myriad of guys who can work on our cars all day long, we are limited to our microscopic ($ by comparison) 'teams'. So to me, rather than make the hard choice of gearing which is expensive and more difficult to change, I'd almost consider some of the other parts easier to swap in and out. Like the turbo for example. It would be interesting to see someone try a 3.1 RP. It would be very laggy I suspect, but you could run say a GTX3076 1.02 E85 and a decent whack of boost. Even increase the c/r and see what happens?

For now I'm going to do a bit of the opposite. I'm going to try the stock 968 gearing with a GT35 sized turbo so the gearing will help the turbo rather than the opposite way around as above.

Savvas, what widebody kit are you using. Any pics or video of your car? 670 tyres are very big for a 944 so I'm guessing you have the full 'Daytona' type widebody rather than the GT2 type flares. What are the details of your build overall?

Thom

Patrick, I think it works the other way around - long gearing will help turbo load earlier, big turbo with short gearing like your set up is a no no, unless you plan running little boost.

333pg333

Yes I see what you mean Thom. I've just been going off my current setup with shorter gearing and GT3076 which seems to work pretty well.

DFASTEST951

Anyone with more than 350hp can really benefit from a taller ring and pinion. That's what i'm doing. I wish a few more of you guys would jump in on this with the rest of us.

TurboTommy

Well, I don't know,
shorter gearing is better with a laggier turbo. Loading the turbo is extremely minor compared to getting the revs up quicker.
This goes for any drive train combination; NA included: The higher up the RPM scale where peak torque is made, the shorter the gearing should be (and possibly also more gears), to better experience the power characteristics of the engine.

That being said, I really don't know why there would be any interest in changing gearing on our cars. This is probably one of the best geared sports cars that has graced our planet in the the last 3 decades: No overdrive BS in top gear and nicely even spaced ratios down to first.
What's more is that the ratios along with the final drive totally suit the modding that we do: we increase torque, but keeping the torque shape essentially the same, maybe extending it to slightly higher RPM; and voila, you have a faster accelerating car that can also reach higher speeds, tweeking it with the diameter of the tires.
You can't improve upon the gearing when there's a good combination of acceleration and a top speed which is achieved a bit past the power peak, barely reaching the limiter, in top gear.
Isn't this the case with most of us?
Gearing a car for a specific track is, of course, a different story.

Duke

I have to agree with you TurboTommy, I don't see the point for a street car unless you're specifically aiming for 200+ mph. You will just end up with less acceleration. Maybe, but just maybe, it would be nice for an autobahn car Thom I think I remember you saying you were driving on the autobahn on regular basis?

Thom

In my case it's not only about increasing top speed - playing with rim/tyre sizes is IMO a bandaid as bigger wheels will necessarily be heavier, well at least real world affordable items, and lower profile tyres will affect road compliance and ruin the ride on the odd back roads.
I am sticking with stock wheel/tyre sizes for these reasons.

I always found the stock gearing too long for the 2.5 in light load situations and below 4000rpm, as the engine always lacked a bit of low down torque and response to feel just fine, which the 3.0 engine nicely compensates for. It is significantly faster and responsive off boost than my 2.5 was, even though I already had the minimum vital upgrades (stock K26/8 but chips, MAF, wastegate, etc)

The original idea of an additional top gear was merely to fully exploit the power of the 3.0 engine at speed, as whenever I had the chance to take it past 6k rpm in 5th gear, the speed at which it built revs convinced me it would grab a fair bit more speed than it does with the stock gearing without much, if any, additional effort.

This doesn't happen that often though, the car is a bit of a handful at those speeds, and this is why this is the sort of mod I will seriously budget on when I have everything else upgraded on the car (exhaust, intake, full Garrett turbo, camshaft, etc). I have been happy with the stock 951 gearing so far and it works perfect with my engine, apart that the engine feels hungry for an extra gear when reaching upper rpm in 5th gear.

Simply adding another gear to the stock 951 trans may feel like an overdrive (which is basically what the 968 trans with Audi 01E diesel gearbox gears would be), this is why I see the factory 968 TS gearing (968 trans + taller R&P + slightly longer 5th and 6th gearing) as the most appropriate solution for my application. The shorter/closer intermediate gears will make the car more drivable at sedate speeds, offer better acceleration, better top speed and better fuel economy on the motorway. The turbo might not load as well and early as with the stock 951 trans, but it just might.

Joe has a lot more power/torque and a fully sorted engine already, so it's time for him to get that longer gearing. Aerodynamics allowing, he should easily see 200mph without revving the hell out of his engine well past 6k rpm.

DFASTEST951

Thom...I concur.

blitz951

Joe,
I still may do this but first need to get my car back. I will need to see how it performs prior to making any other changes. The car has been totally modified/changed and even as I look at this tranny option last week my final change was not use my Turbonetics turbo and go with a gt35. Let me see how this car performs then I will get back to this. I will be watching this thread with interest so if you make this change let us know how it goes.

scottmandu

JH motorsports does not sell gearsets for the 2WD gearboxes, only the 4WD boxes.. They are not the same!

George D

Thanks.....If I placed the order, I would have been PISSED if it was the wrong part.

I left you a message, did you get it?

George D

Garrity will be calling you today. Thanks!