924Board.org

[Timmay!]

Nope.
Even with 700 HP, If you spin the wheels on upshifting, it's because you let the clutch out too quickly or at the wrong time with respect to the throttle application.
On downshifting, it's not like the main shaft of the tranny is going to slow way down in the time it takes you to drop a gear.
Matching revs well will ensure a smooth downshift.
If I've done a downshift perfectly with heel and toe, you can't even feel it. That's my goal when I race on both upshifts and downshifts - a seamless transition.
_________________
Current project 1981 931
944 spec # 22 924S
77 924 Martini. Rescued. Sold
88 924S SE. Rescued. Sold
PCA since 1985

[edredas]

Oh well, I've got a feeling that this will never end... I was taught that way, right or wrong... you don't have to do it. I just thought that you and others would like to know why it is actually done.

This is from another driver that I had contacted to see what he had to say...

"...a simple rev match will smooth the transition between the gear change but, it doesn't fully disengage the drivetrain as the car is still 'technically' in gear (albeit with clutch down.) The layshaft is not brought up to speed and the whole process has been a 'shortcut'. The result will be weight transfer and that means a loss of stability. Of course rev matching helps with stability but it is no where near as effective in terms of stability management or acceleration as a double-clutch."
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Timmay!]

I hear ya.
There's more than one way to do it, but I still say you're wasting lap time by double clutching.
_________________
Current project 1981 931
944 spec # 22 924S
77 924 Martini. Rescued. Sold
88 924S SE. Rescued. Sold
PCA since 1985

[edredas]

Oh ok, I think I see what you saying now.... actually, you learn to drive differently with this technique. Yes your shifts are slightly slower, but you shift less which saves far more time.

When you're coming up on a turn where you need to be in a much lower gear for the apex is about the only time this would be used. Single-clutching basically makes you wait for the wheels to slow down enough so the synrcos will let you into the next lower gear.

If the speed of the gear you're selecting, and the speed of your layshaft are too different, then gears will grind or the syncros will kick you back into neutral. So you have to slow down/clutch into the next lower gear, one by one... skipping a gear may cause them grind since the layshaft is too slow to go in that gear.... it's also harder to smooth out the shifts when skipping gears this way.

This is actually slowing you down more since you're braking early and trying to get down through the gears. If you see what I mean...

When double-clutching, you don't have this problem since you're not using the syncros. By directly controlling the speed of the layshaft you can make it go in any gear smoothly... so you can just stay in 5th, hammer the brakes and double-clutch down to 2nd and go.

When done correctly you won't have much time while braking to shift more than once. While I've heard this can be achieved on single clutch, I would not try it! 5th gear might be at 1000rpms and you want to be second gear which is spinning at 3500rpms. There is no way to make this a smooth transition with a single-clutch... so either your gears will grind and prevent you from engaging that gear, or you'll go in that gear and the days on your transmission are now numbered...

I hope that now makes better sense.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[ronined]

Timmay,

Nice video!

I heard the heel-toe down shifts the first time, saw them the second time. Enjoyed it all over again a third time. Nice!

There are few things nicer than a properly executed heel-toe downshift.
_________________
'87 924S

[minnesotamatt]

hey i just wanna replace the muffler, is that ok? i bought a 2.25 cherrybomb glasspack, what do I need to do to install it?

[bcblase]

A metal cutting saw and a welder would be a good start...
I would stay away from clamps.

A local exhaust shop will only charge you a few bucks to install it properly.
_________________
1987 Porsche 924S - track toy
1986 Mercedes 190E 2.3-16v - autocross
2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver