lawjdc

Does anybody know what rpm level the optimum shift point for third to fourth gear is? Assume a 2007 GT3 and a level track.

GrantG

8,400

lawjdc

no, seriously . . .

GrantG

I'm not kidding. The gear ratios in the standard box are spaced wide enough that you want to redline (if you're going for top performance over preseving the motor for your kids) to maximize the revs in the next gear after you upshift.

Condor Man

I would have thought somehwere between 6,500 - 8,000rpm. Your revs should never fall below when you are on the limit.

GrantG

Yes, you want to keep your revs above 6,500 all the time on the track (if possible), but if you shift at 6,500 in 3rd and land in 4th your revs in 4th will be far below 6,500. So, that is why you want to shift at redline. Even though redline is past the power peak, you want to make sure you're not too far below the power peak in 4th. Shifting at redline makes sure you spend as much time as possible as close to the power peak as possible (this is what you want for max performance).

997gt3north

this is correct
- 8400 for max performance
- 2400 if you are donating it to your grand children

chago996

At the rpm that gives max HP output, so that rpm then falls on range of max torque as you shift gear, which will make the engine internals speed up again to max HP output rpm as fast as possibly designed, so that u can do it all over again on next gear, with your hair on fire, screaming YEEEHAAAWW! Horsepower gives u speed while torque gives u acceleration.

Jake951

Staying in the gear that delivers maximum horsepower to the rear wheels ALWAYS maximizes acceleration. This is a consequence of basic physics. In practice, this works out to shifting at redline, as others have pointed out.

timothyli

How about look at the yellow triangle up shift indicator. At what rpm does this indicator light up?

Carrera GT

Who comes up with this 6500 rpm stuff?

GrantG

I was responding to someone else who mentioned that number. I said you wanted to be above that (did mean to say that's an important number). As I said before, as close to power peak for as long as possible is the goal when accelerating.

NJ-GT

The idea is to maximize power to the wheels at all speeds. This is data from the 2010 GT3 RS, using a 335/30R18 tire. Note that only 4th, 5th and 6th are close ratio, everything else is spaced out drastically (and it is worse in the standard GT3 due to the 3.44 R&P).


2010 GT3 RS (Stock) 25.6" Hoosier A6 335/30R18 A6
Gear, Ratio, Max Speed, RPM drop on upshift at Redline
1st 3.82 44
2nd 2.26 74 5000
3rd 1.64 102 6200
4th 1.29 129 6700
5th 1.06 157 7000
6th 0.88 189 7100
Final Ratio 3.89
Redline 8500

Using this gearing information with a 100rpm split (speed in gear) and an Excel pivot table with the power to the wheels every 100 rpm (from dyno graph), you can identify the ideal shift points for the 2010 GT3 RS, which by the way is 8,500 rpm in every single gear.

At 45mph (typical low speed track turn) it is impossible to keep the RS on the powerband, the car will be bogging at 5,200rpm in 2nd gear putting 250rwhp from the 415rwhp available, but nothing can be done here due to the long spacing for the first 3 gears.

Using the same cross reference of gearing/speed and power/rpm you can determine the ideal gearing for a 6-speed transmission. The GT3 has a very narrow powerband, so it would benefit from a 8-speed transmission with very close ratios (one of those DCT close-ratio like the M3 and F458). But given the restriction to a 6-speed manual, gearing has to be compromised.

In the 997 GT3 Cup, gearing is optimized for track use, and with only 6 gears available, Porsche decided to use a very long 1st gear (3.16) and a very short 6th gear (.96) with an even shorter R&P (4.00:1), the 997 GT3 Cup cannot even reach 180mph despite of the very tall 26.85" rear tire. However, having a long 1st and a short 6th allows for better spacing in all the gears, and the Cup car (well driven) rated at 450Hp same as the street car, puts more power to wheels at a given speed than the street car. Even if you get a 2010 GT3 RS down to Cup car weight, the Cup will still accelerate better because its graph of power at speed has a larger area under the curve. At 45mph, the 997 GT3 Cup can use 1st gear, and it puts down almost 400rwhp while the 2010 GT3 RS is just running at 250rwhp, and both engines are rated at 450Hp.

MM3.9GT3

The reason we pay a premium for the GT3 over a C2S with PDK is to shift at 8400 rpm and hear that glorious sound (and for the dry sump )

See below for the 997.1 GT3 Torque curve. Note that peak torque is at 5500 rpm. When you upshift, make sure you don't drop below 5500 rpm.


http://myautoworld.com/auto/porsche/...he-07-gt3.html

Antonov

I always wondered why Porsche designed the GT3 to have such a high vmax. Seems counter intuitive for a relatively under power road race oriented car. Perhaps fuel economy....

Re gearing the transmission is probably a very expensive solution. Has anyone tried fitting a higher final drive? Seems like it would be a very worth while track mod, and not difficult to do if you're already in there doing a diff.

-Dino