PV

Lets discuss the rev limiter: why is the 997 limited at 7200 rpm and not 8000+ as in other "standard" road cars?

Is it the weight of the valves, or the control software, or the speed of the injectors, or the spark speed and power, or the fuel type......

NITEALB

why rev to 7200 anyway, isn't peak hp developed at 6800rpm? i'm assuming that to get the most power u wanna shift at or around peak hp. correct me if i'm wrong cos really i ain't got a clue, just relying on wot people at track days have mentioned.

Chris C.

For maximum acceleration, you want to shift at the correct rpm such that when you let the clutch out in the new gear you are at peak torque. Divide the 2 gear ratios (i.e. 2nd to 3rd) and multiply by peak torque to find the optimal shoft point in each gear. HINT- It's rarely redline.

Now--what road cars do you know that rev to 8000? Only m3 and mazda rotaties come to mind...

P997C2S

The Honda S2000 roadster will spin-up to 8,000 rpm before the rev limiter kicks in. It produces its peak HP at 7,800 rpm.

Chris C.

True. Forgot that one....but in that case, the car has little torque at any rpm, so it needs to. The latest flat 6s have plenty of torque down low and don't need the revs to make adequate power.

PV

6800 rpm is max power, but not max speed in a particular gear.

PV

M5, Ferrari's

PV

Still the question: why a limit?

MJones

Really simple:
The engineers who design the engine feel that this is the maximum safe RPM for the engine internals.

The GT3 has a higher redline because it's engine internals are stronger and lighter with less reciprocating mass.

Need we second guess the mechanical engineers who design these engines?

BTW heres what you can acheive with a NA 3.8

TECHNICAL SPECIFICATIONS
Porsche Daytona Prototype 3.8-liter power plant

•ENGINE: Six-Cylinder Boxer Porsche 3795 cc - 76.4mm stroke, 102.7mm bore
•Horsepower: 510 @ 8500 rpm
•Torque: 435 N/meters @ 7500 rpm
•Max RPM: 9000
•Cooling: Water Cooled
•Intake System: Six Individual Throttle Valves
•Fuel Injection: Sequential multi-point Bosch MS 4.0 system with ignition control
•Lubrication: Dry Sump with Heat Exchanger and Mobil 1 oil

Coochas

Add to the list, the next Audi RS4, I believe it is a naturally aspirated V8 that revs to about 8500!
Also, I don't know about these days but all three Rx7s (80,84,88) I owned redlined at 7000.

AeroSmith

X51 revs to 7,400. That's pretty close to 8,000.

I have to say, however, it seems faster to shift just at or before 7,000.

Torque peaks at 5,500 in the X51 and starts to drop off rapidly above 6,500 RPM. Torque drops off rapidly in the non-X51 above 6,500 as well. It almost seems as if 6,500 might therefore be a good shift point in any Carrera S.

NITEALB

I agree with aerosmith, shifting at around 65-6600rpm seems to be the fastest way to accelerate. but based on what ChrisC said about dividing gear ratios and multiplying by peak torque (4600rpm) to get the fastest acceleration the numbers are different. with the numbers below i guess that shifting at redline in first, aprox 6600 rpm for 2nd, 5800rpm for 3rd and 5500rpm for 4th to 5th. or am just reading this all wrong? so, in terms of accelerating the fastest, is it better to shift at 6600rpm, or the staggered rpm's using the gear ratios? in addition, if its easier to go faster by shifting at less than red line, whats the point having a red line past so many rpms past the ideal shift points? anyone care to educate me?

1st Gear Ratio 3.91:1
2nd Gear Ratio 2.32:1
3rd Gear Ratio 1.61:1
4th Gear Ratio 1.28:1
5th Gear Ratio 1.08:1
6th Gear Ratio 0.88:1

PV

top speed

GrantG

Redline (or very close) will be the fastest...

PV

Not necessarily for acceleration, but certainly for top speed. So, the question: what is the ultimate technical reason not to increase the rev limit? Is it valve weight, electronics (can't be), valve lifting pressure, ....?