audipwr1

Should I put in a clutch stop to help with that?

The speed by which I can angle my foot is pretty slow due to injuries

Are you you putting pressure on the shifter as you DIP the clutch in to feel for slack?

RickyBobby

OP I've been told my shifts needed to get more "crisp" and have tried to work on this skill in the past year. Obvi I'm nowhere near VR and Cory and Andy, but I did make some progress by taking Peter's advice on "dipping" the clutch.

I did this by practicing with the engine off, car parked in the garage, 5 min a day just before bedtime. When I got on track, the "muscle memory" gained was helpful. I hadn't thought of a clutch stop, but that might be my next step.

winders

915's aren't bad....you just have to be deliberate. You have to give the synchros time to do their job, that's all.

ProCoach

Here's the proper way to shift a 915 (or any other) 'box.


Here's a good 901 'box vid, same driver.

winders

Peter,

The 915, with its balk-ring synchros, needs to be upshifted and downshifted slower than a box with Borg-Warner synchros. Simple fact.

winders

P.S. Well, shift slower if you want the synchros to live for a reasonable time. If you have the budget to have the box rebuilt every 10 hours or so, shift as fast as you want.

ProCoach

Scott, with more than thirty years of rebuilding Alfa Romeo Porsche-style baulk-ring synchros, I'm quite familiar with how they work and how long they CAN last.

I refer you and the other doubters to the 915 video above between 1:18 and 1:48.

This is the shift speed people need in order to reach the optimal level.

audipwr1

Any videos showing feet and hands?

RickyBobby

Peter I'm curious: is "dipping" the clutch in a 915 transmission possible? My pcar has a 915 (my DD) but have only "dipped" in my relatively modern race car.

winders

Peter,

I have a 915 in my race car and I KNOW what happens when you shift them too fast. How many race cars have you raced with a 915?

Don't tell me what I don't know.

You certainly can shift a box with borg-warner synchros faster and what is ideal for a BW box is certainly not ideal for a 915.

Jeez.....

Slakker

Yes. I think this is an important distinction to make, especially for less experienced drivers. Lots of money shifts in the 996 forum lately, including one of my own, has me a little paranoid lately. And sounds like I underestimated the amount of time crisper shifts can save. Always good stuff here.

audipwr1

6/10s this issue is costing me so it's big

Beantown Kman

audipwr1-- I'm curious to understand how you learned how slow your upshifts are. Did someone ride with you? Did you look at your data?

Less than optimal shifting technique is very evident in the data. When I first looked at the difference between good shifting and really good shifting I was shocked to see how much time is lost in this seemingly simple skill. ProCoach was the first to point this out to me.

audipwr1

Yes data

Time off throttle and decrease in speed relative to pro driver in my car 5 minutes before

Also can see clutch slipping by seeing squiggly speed versus full throttle on release

ProCoach

I'm at Daytona right now. Here is pro in the car (red) and the owner (blue) coming out of Turn 6 onto the banking and up to the Bus Stop.

There's speed, so you can see the drop, and there is longitudinal g, which shows the thrust force forward (or not).

They start the same, and each shift the blue drops.

You can see the "cessation in acceleration" (Beantown KMan, remember that concept? ) in every v-shaped dip in the longitudinal g.

Notice, almost no dip in the red trace and almost imperceptible drop in speed at each shift. Blue? Not so much.

This is in a 2.5 liter 911 (ST spec) with a 901 gearbox.