francisluu

I never noticed this when I had a 993 and only started to see excessive bounce with the tachometer needle after installing a mid weight flywheel on my 1990 C4. Those revs go up quick now!!

ive definitely seen this on older cars just driving around normally changing gears. Any idea if this is something that's a straight forward fix?

Achtung964

Don't have the fix for that but those revs are quick! Which flywheel did you go with?

francisluu

Thanks @Achtung964 .

@NineMeister offers a midweight flywheel option. It's feels pretty perfect. Not so lightweight and aggressive as the typical lightweight option that a lot of people go with but still gives you a huge upgrade in response. And the gearbox chatter

It feels quite similar to my 997.2 GT3 with the RS 4.0 lightweight flywheel.

ToreB

I see the same tachometer needle behaviour when I quickly turn up the revs in my tachometer test bench.
The instrument galvanometer design has certain rotating weight, and a quick and large change of current in the electromagnet will cause a rotational force that will make the needle to overshoot. This is especially visible when you press the pedal hard and immediately release it. The dampening effect of the rotational weight (and electronic circuit) is adjusted to match the normal engine characteristics. It may be possible to make some sort of electronic dampening circuit to counteract this behaviour, but you could run into problems finding anyone that would like to do this for you.
All the best,
Tore

NineMeister

My only other thought is that when the MWF flywheel was installed, did you check or reset the flywheel speed sensor gap tot the trigger ring? The correct gap is 0.8mm and from experience any variation on this can cause over/under voltage on the signal which may contribute to the over response. As I said, it's just a thought...

Gregg-K

As Tore said, the problem is a damping issue: many automotive instruments have an internal damper to prevent needle overshoot on a sudden transient. The challenge is to damp the movement enough to prevent overshoot, but not so much that the indication can't accurately track engine speed. I've always felt that my C2's tach damping was near perfect, and it could be that your tach has a problem with its damper.
What makes me think this way is that the needle on your C4 seems to oscillate quite visibly when it hits max revs, and the faster the transient, the more it oscillates at max. Perhaps you can sub un another tach to see it if behaves the same way.
Did the tach display this behavior prior to the new flywheel being installed? If so, could be that the tach's internals need attention.
.. Gregg

Bill Verburg

Bouncy tach can be fixed by a good instrument shop
N Hollywood comes to mind

Spyerx

Interesting. I don't see this on my 964 tach with LWFW. Could be tach needs some service.
I also have a 964 type stepper motor on my 71 tach and don't see this (SUPER revvy, 8200 rpm redline)
But if you don't see this under normal driving conditions I'd leave it be.