2ndof2

According to the seller of a vehicle I'm considering which has been 100% Porsche dealer serviced since day one, he downshifted from 6th to 4th at about 100mph after "panicking" when he saw a police car right behind him pulling onto a freeway merge. (says he'd just gotten a ticket the week before) Anyhow, the car had trouble shifting down from 6th or 5th after that. $3,500 later after having the dealer rebuild whatever he broke (I'll be getting a general printout from the Porsche dealer soon but it may lack alot of detail about that particular repair), he said the car is doing fine. What I would like to know is how likely it is he over-revved the motor when that happened or if he did something else. The way he described it is he missed a shift and in all probability the rev-limiter would have saved the motor from damage since he didn't engage the gear under decelerration/load. Does the '95 have an on-board computer that might tell if the car has been over-revved or hit the limiter? If not, what's likely caused the gearing problem? He said it shifted up through the gears no problem but still had it fixed anyway since the downshifting was a problem.

Mark in Baltimore

I can't answer all of your questions, but I'm fairly sure that the rev limiter will not help against missed shifts; it will do its job if you bump past redline while on the throttle. Countless Porsche drivers have selected the wrong gear and blown their engines, despite the presence of a rev limiter.

Greg Fishman

6th to 4th at 100mph would not result in an over rev. If he hit 2nd that is another story...

Glen

6th to 4th....damage...lol

BS911

Correct me if I'm wrong but if you hit 4 coming from 6, you were either intending on 4 to begin with ... or 2nd. If the story was that he accidentally hit 3 instead of 5 then maybe. Even 3 at 100mph isn't severely stretching the rpms. Combine that with some (hopefully obvious) braking and the rpm hit is minimal. So maybe the problem isn't of an overrev nature, but a "forgot to hit the clutch" nature and he just did some serious grinding and broke some teeth? Or in the panic he overmuscled the shift rods and bent some stuff.

Glen

Seriously, just post the invoice and we will tell You what happened most probably. There will be some telltale clues in there.

Ms Kita

I'm certainly not a mechanic, but I have downshifted and missed before. It would be hard to convince me that downshifting from 6th to 4th in any six speed manual would cause severe damage.

Just my opinion,
Ms Kita

kary993

You would need to be over 125 when you shifted from 6 to 4 to get close to over reving the motor.

mrmickeymouse

I am no sure about you 993 guy's but, Boxsters and 996's have an ECU that will remember redline cut out shifts.

I am thinking of switching to 993 power. I need power.... more power..104% and throttle up, oh...oh...

KRA993tt

Sorry I don't know if or what the difference is between a 993 na and my tt but I hit the rev limiter in fourth around 122 mph, it can't be that different. I doubt a 6 to 4 shift was the reason for a problem. Something is missing in the story.

Tom W

6th gear at 100 mph is about 3500 rpm. Redline (6800 rpm) in 3rd is 104 mph. If he was at 100 mph, 6th to 4th would not be an issue at all (it's about 5200 rpm). Redline in 4th is about 130 mph.

Kieth's tt has a different gearbox than ours and the calculator says his redline is 121 mph in 4th, pretty close to what he reports

I can't see getting damage as described. Now if he was going 115 mph and actually hit 3rd instead of 5th, that would be a problem.

FlyYellow

it sounds more like he chipped a tooth on the tranny rather than over rev'ed the motor...

cheers,
boris

Benton

I bet he dropped the clutch before he completely put it in 4th. I've heard that noise before with a friend driving their car = not good.

Chris W. - '96 Targa

Interesting. 3rd in my car runs up over 110, close to 115 (shifting at indicated redline on my tach, with no rev limiter interruption).

I agree with all the others, a [properly executed] shift from 6th to 4th at 100 MPH wouldn't cause any problems.

-Chris

Tom W

Chris, the mph I posted was calculated based on gear ratios and tire size (I used a 24.9 inch diameter). It will vary a few mph as the tire size changes. I'm suprised at your observed speed at redline as I find it's a pretty close estimate for my gear ratios (custom, not G50/20). For me, redline in 3rd is about 90 mph and 4th is about 115.