AsianBond

My speedo is not that accurate. Does anyone know what speed they're doing at 4000 rpm in 4th and 5th gear?

Anyone get up to 5000 rpm in 5th gear?

I have a 91 C2, 17 inch tires.

DaveK

I've been well beyond 5K rpm in 5th - but I'm afraid I can't remember how fast I was going at 5K rpm. I do know you hit the rev limiter in 4th at an indicated 140mph - so I would guess it's somewhere around there.

john thompson

I know this one.....in my car at 4000rpm (that is straight up, right?) my speedo showing 100mph.

John
Rockport, Tx

DaveK

Ah - I didn't read properly. I agree - 4K rpm is 100mph in mine too (although according to the GPS camera detector, it's more like 95).

john thompson

Whoops, I omitted that I was in 5th gear.....so

4000 rpm....5th gear....equals 100 mph.

John

joey bagadonuts

Okay, this a C4 gear/rpm curve, but the C2's 1st, 4th and 5th gears have the same ratios. This would be a benchmark, i.e. what you should be doing. The C2 chart can also be found in your owner's manual.

springer3

Speedometer calibration is a joke. Almost all car makers, including Porsche, have speedometers and odometers that read high. DaveK's GPS shows his is too high by 5.3% (indicating 100 when speed is 95). Most are off by more than that (up to 10% in some cases). Mercedes speedometers used to be dead-on, but even they changed to read too high. Reasons:

1) Warranty expires sooner

2) Owner happy because he/she appears to get better gas mileage

3) Owner happy because he/she appears to have a faster car

4) Owner happy because car appears to last for more miles

5) Dealer happy because of more frequent maintenance visits

6) Fewer speeding tickets, and tickets received are a relief when the officer clocks you at lower speed that your believed you were going

Speedometers are now digital, and calibration should not drift. The factory setting is modified by the actual tire diameter. There are small changes as the tires wear or tire pressure changes. Deliberate calibration error for reasons stated above is well in excess of the variation due to tire pressure and wear.

Adrian

Do not forget that 1991 model years and up use the ABS wheel speed sensors to calculate driving speed. Wheel and tyre rolling diameter play a critical part in speedo accuracy.
6% permitted wheel speed differential is quite a lot added to instrument error of a up to 5%. That is a 11% differential between actual driving speed and indicated driving speed.
Ciao,
Adrian
964C4

AsianBond

As always, thanks guys.

I think my speedo is quite off, I recently did 250kph on the speedo but the tach was at about 6000rpm in 5th gear. And the car still felt like pulling some more.

Anyone ever max out there 964? Top speed?

Adrian

162 mph indicated (260 kph), speedo pointer steady.
Ciao,
Adrian
964C4

John Boggiano

I've had mine at the redline with the speedo showing 185mph. I reckon on that being in agreement with Adrian's figure in reality.

AsianBond

John, very nice. Makes you appreciate the great engineering from a 3.6 liter N/A motor. No turbos or fancy electronics needed here.....

John Boggiano

That's right - at top speed, the engine settled down to a purposeful hum, car rock steady. Beautiful.

Edit: My mistake - it was a couple of years ago - it looks like I should have said 175mph. Mind you, the needle would look slightly further on from a driver's-eye-view. AND, my chip does allow me to exceed the redline slightly. Pretty sure I do remember it passing 180...

ian c - u.k

i have a programme .

give me gear ratios , final drive ratio , and tyre size .
i can tell you speed for any given rpm , or vice versa , in any gear.

handy when you are picking cams and gear ratios

AsianBond

I assume stock ratios. Running 215/45/17 fr and 255/40/17 in back.
91 C2 manual, euro version rhd.

Like to know 4000, 5000, 6000 rpm in 4th and 5th gear