Clutch Question G50 911 3.2

[Wangan]

Hey all,

May be a silly question, but I'd really appreciate some feedback from someone more mechanically minded than myself.

I've been learning to rev match in my G50 3.2 Carrera and a few times while going from 3rd to 2nd in a corner, I've got the timing a little wrong and have accelerated as I've released the clutch. I believe it's called riding the clutch. It's happend 5 or 6 times. I know it's ok to do it a little bit in 1st to 2nd, but what about down shifting from 5-3 and 3-2.

My question is can I/have I done any damage to the car?

Thanks.

[Techno Duck]

You can potentially glaze the disc which would cause the clutch to slip. But you would really have to be riding the clutch for a while to make this happen.

Just take care that you don't accidentally do a mechanical over rev with a misshift or getting the timing wrong.

[Wangan]

Originally Posted by Techno Duck

You can potentially glaze the disc which would cause the clutch to slip. But you would really have to be riding the clutch for a while to make this happen.

Just take care that you don't accidentally do a mechanical over rev with a misshift or getting the timing wrong.

Thanks for the reply.
Interesting point regarding the over rev. I haven't gone over 60mph, so hypothetically if I move from 5th to 2nd at 60mph would that overrev? I think the G50 can do 60mph in 2nd. You would only over rev going into first gear, which is locked out? Providing I keep it under 60.

[PeteKz]

Ditto what Jon said. Just don't over-rev it. "Slipping the clutch"" a bit going in and out of gears isn't a biggie. It will reduce the life of the clutch a little bit, but otherise won't hurt anything. You have to slip the clutch to get going from a stop in 1st gear every time, right? That wears the clutch a lot more than occasional slips in between 2nd, 3rd, 4th or 5th.

[Wangan]

Originally Posted by PeteKz

Ditto what Jon said. Just don't over-rev it. "Slipping the clutch"" a bit going in and out of gears isn't a biggie. It will reduce the life of the clutch a little bit, but otherise won't hurt anything. You have to slip the clutch to get going from a stop in 1st gear every time, right? That wears the clutch a lot more than occasional slips in between 2nd, 3rd, 4th or 5th.

Thanks for the reply. See my above post regarding the overrev. Is my logic correct?

[PeteKz]

Your logic is correct. But it's easy for you to figure out: see what your road speed is in 2nd gear at 1/2 of your redline RPM. If it's 30MPH or more, you didn't exceed redline at 60PH. If you did slightly, don't worry about it.

The mechanical limit of these engines is considerably more than the redline on your tachometer. That redline is set to leave a margin of safety, as well as to tell you that the stock engine doesn't generate more power beyond that number. People routinely run the stock internals in modified engines to 8000 RPM. You should not have got anywhere near that.

Spend more time driving your car, and less time worrying about it.

[Wangan]

Originally Posted by PeteKz

Your logic is correct. But it's easy for you to figure out: see what your road speed is in 2nd gear at 1/2 of your redline RPM. If it's 30MPH or more, you didn't exceed redline at 60PH. If you did slightly, don't worry about it.

The mechanical limit of these engines is considerably more than the redline on your tachometer. That redline is set to leave a margin of safety, as well as to tell you that the stock engine doesn't generate more power beyond that number. People routinely run the stock internals in modified engines to 8000 RPM. You should not have got anywhere near that.

Spend more time driving your car, and less time worrying about it.

Thanks for that. Not too worried. More interested really. My car is at the shop, so have looked online a little as I cannot test.

Thanks for that.

I found some charts it another thread. Going from 5th to 2nd gear at 60mph, because 1st would be locked out and that would would still Hypothetically be under redline?

This chart shows top speed of 2nd gear is 69mph or 64mph. Can't tell which is correct.

Anyone able to confirm?

[spuggy]

Originally Posted by PeteKz

The mechanical limit of these engines is considerably more than the redline on your tachometer. That redline is set to leave a margin of safety, as well as to tell you that the stock engine doesn't generate more power beyond that number. People routinely run the stock internals in modified engines to 8000 RPM.

3.2/3.3 rod bolts are undersized (relative to both earlier and later cars), and notoriously weak/prone to letting go because the bolt stretches - esp. when over-rev'd. This, should you do it, will cost you a spun big end bearing, a crank journal and a rod. And very probably a piston & cylinder.

The bottom end is fairly stout/reliable in normal usage - but I venture to say that absolutely no-one runs 3.2/3.3 bottom ends @ 8000 RPM with stock internals. There's a reason ARP and Raceware make rod bolts for these motors (which are also re-usable, because they don't exceed their elastic limit when correctly fitted, unlike the factory single-use bolts).

Peak HP on SC/3.2 cams is quoted by the factory at 5500 RPM for both cars. The car doesn't make any more power beyond that without additional work - including replacing those cams, because they're done by then.

And as for there being more "margin" in the redline number - that may be so (despite the fact that there's little point revving that high, according to the dyno chars). But the redline is set where the factory quotes maximum permissible engine speed.

Popping the RPM up from 4K to 6K on a downshift? Well, that's not really how it should be done. But it's not going to hurt anything - and how are you supposed to practice/learn to do it right?

You could buy a much cheaper manual transmission car and practice in that, I suppose...

Originally Posted by PeteKz

Spend more time driving your car, and less time worrying about it.

Yeh, this.

[pmax]

Originally Posted by Wangan

Hey all,

May be a silly question, but I'd really appreciate some feedback from someone more mechanically minded than myself.

I've been learning to rev match in my G50 3.2 Carrera and a few times while going from 3rd to 2nd in a corner, I've got the timing a little wrong and have accelerated as I've released the clutch. I believe it's called riding the clutch. It's happend 5 or 6 times. I know it's ok to do it a little bit in 1st to 2nd, but what about down shifting from 5-3 and 3-2.

My question is can I/have I done any damage to the car?

Thanks.

Don't worry about a few RPM mismatches here and there ... assuming you aren't on a racetrack running at redline pedal to the metal !

Besides, the clutch is a just another wear and tear item.

[spuggy]

Originally Posted by Wangan

TI've got the timing a little wrong and have accelerated as I've released the clutch. I believe it's called riding the clutch. It's happend 5 or 6 times. I know it's ok to do it a little bit in 1st to 2nd, but what about down shifting from 5-3 and 3-2.

I presume mean by "accelerated" that you mean that the motor speed increased as the wheels drove the RPM up?

When I hear the phrase "riding the clutch", I think of someone staying stationary on a hill start by slipping the clutch without using the handbrake. They don't like that.

If RPM are increasing beyond your intended range on the downshift when the clutch is let out, you're down-shifting too early/too fast, or not letting the motor slow enough during shifting before you let the clutch out. Or some combination of "all of the above".

The whole point of blipping the throttle on the downshift is to match RPMs of the motor and transmission to the speed of the road wheels. Nothing should snatch.

Double de-clutching makes this smoother/reducing weight transfer and reduces wear on the transmission internals. The process is:

• depress the clutch
• shift into neutral
• release the clutch & blip the throttle
• depress the clutch
• shift into the desired lower gear
• blip the throttle
• release the clutch

(What you do next with the throttle depends entirely on whether you intend to accelerate or continue decelerating...)

Blipping the throttle with neutral selected spins up the gear shafts to a higher RPM - which then makes selection of the lower gear much easier, and reduces the work the synchros have to do (otherwise they have to do the work to match the speed of the two shafts before the gears can engage).

In fact, with a 915 with worn out synchros and missing dog teeth, this might be the only way you can get a good downshift.

G50's don't suffer as much. But synchros and dogs are still wear items - and they aren't cheap - so once once you've rebuilt one and know how much they cost, you'll have a pretty strong incentive to learn how to minimize transmission wear...

Being correctly speed-matched means there's minimal weight transfer when the clutch is released in drive. Otherwise, the rear digs in - eg if the wheels are driving the motor. And this will unsettle the weight distribution of the car - smooth is fast.

Ideally, use heel'n'toe to slow the car and double-clutch the downshift, maximizing control and minimizing transmission wear. If your downshifts are too fast, that ought to slow you down some

Originally Posted by Wangan

I found some charts it another thread. Going from 5th to 2nd gear at 60mph,

With a G50 you don't strictly need to "rock the box" (select through every intermediate gear without letting the clutch out) like many say really helps a 915 achieve optimal shifting.

I still do it, sometimes, out of habit...

Originally Posted by Wangan

because 1st would be locked out and that would would still Hypothetically be under redline?

"Locked out"? There ain't no "locked out"...

Given enough power to move the motor/trans mounts (and thus the gate) around enough, even an incredibly sloppy/tired 915 will select 1st gear at 80+ MPH.

This is one way people have been known to spin rod bearings.

Originally Posted by Wangan

This chart shows top speed of 2nd gear is 69mph or 64mph. Can't tell which is correct.

Anyone able to confirm?

You're going about this wrong, IMHO. You shouldn't be shifting down intending to end up at redline in the lower gear. Aim for 3-4K RPM or so in the lower gear instead - right around peak torque in case you want to accelerate again, plenty of buffer to redline if you misjudge it a bit.

You're aiming for zero jerk/weight transfer when you let the clutch out - that's what "RPM matching" means. Work towards that. And don't be discouraged that you can't do footwork like Walter Röhrl right away:




You might like to take a look at "Porsche High-Performance Driving Handbook" by "Quick Vic" Elford.

Stuffed full of history/anecdotes - and some very clearly explained sections on techniques to maximize control while driving fast, and how/why they work.

If you can drive fast on snow/gravel/mud, driving on tarmac is a breeze in comparison...

[PeteKz]

Originally Posted by spuggy

3.2/3.3 rod bolts are oversized (relative to both earlier and later cars), and notoriously weak/prone to letting go because the bolt stretches - esp. when over-rev'd. This, should you do it, will cost you a spun big end bearing, a crank journal and a rod. And very probably a piston & cylinder.

The bottom end is fairly stout/reliable in normal usage - but I venture to say that absolutely no-one runs 3.2/3.3 bottom ends @ 8000 RPM with stock internals. There's a reason ARP and Raceware make rod bolts for these motors (which are also re-usable, because they don't exceed their elastic limit when correctly fitted, unlike the factory single-use bolts).

Spuggy, yeah, for some reason I was thinking it was a 3.0 which will take the higher revs. Anyway, he didn't hurt his engine. BTW, the rod bolts are "undersized" relative to the 3.0. I'm sure that was a typo.

[spuggy]

Originally Posted by PeteKz

Anyway, he didn't hurt his engine.

OP seems to be planning downshifts to arrive at redline in the lower gear. That'll not end well, I think... Plus I don't really see how it's useful.

Originally Posted by PeteKz

BTW, the rod bolts are "undersized" relative to the 3.0. I'm sure that was a typo.

Oh, duh. Typed the exact opposite of what I meant. Correcting that, thanks.