Benton

That's awesome. Thanks for the input, Greg.

38D

I don't think there is any point in double clutching if your synchros are still working.


Exactly.

jgrant

I might be the only one, but even though I'd heard of it many times, I didn't really understand what double-clutching was until reading this... it may help: http://en.wikipedia.org/wiki/Double_clutch

brucegre

Good description, but realize that you do not need to double clutch in order to heel and toe. Heel and toe is a balance technique to match engine speed to road speed so you don't upset the car under braking. Double clutching is an input to output matching so you can shift without graunching. In both the cup car and the stock GT3, the synchros do the job wonderfully.

911pcars

Having driven neither a cup car or a GT3 (I'm deprived), I'm not sure of the longevity of the synchros in these gearboxes. I have no doubt they're superior to what I'm using now. Nevertheless, synchromesh assemblies are wear items and the more a synchro is called into play to synchronize gear speeds, the more it wears .... period. Last I heard, rebuilding a gearbox is at least a $1000 bill. On a Cup or GT3, probably a multiple of at least 2. Maybe it's a different generation or audience, the Cup owners, but I prefer extending this eventual date with rebuilding for as long as I can.

It's becoming such a lost skill, some people no longer know how to do it or pass it along to the uninitiated. I was browsing an article in the latest Sport Compact Car mag on the newstand and young grasshopper tech editor was trying to explain the mechanics of double clutching. Nice try attempting to impart knowledge to the fuzzy chin car owners, but he eventually decided it wasn't worth doing with modern synchros to carry the load.

As I recall, he accurately described upshifts as not requiring a throttle blip before the snick into the next gear but repeated the mantra when he described no throttle blip was necessary on downshifts as long as the shift lever was in neutral with the clutch engaged (pedal up). He thought this action alone would bring the internals up to proper gear-changing speeds (the historically-accepted practice is to blip the throttle in neutral, clutch pedal up, to increase input shaft speed to the rotational speed of the next lower gear; see the wikipedia link). To-be-meshed gears rotating at the same speed require minimal synchro involvement. I'm hoping young grasshopper receives enough fan mail to correct himself in the next issue and unfuddle befuddled minds who read this, but I'm not holding my breathe.

Do the next owner a favor. Save the Synchros .... unless you maybe drive a Cup or GT3 car and your last name is Luhr, Maassen, Lieb, Bergmeister, Bernhard, Leh, Henzler or Andretti (sorry if I left any significant names out) :-)

Sherwood
Early 911
http://members.rennlist.org/911pcars

Mikey

Sweet video! Just curious, does your motor look a lot like this under the hood? How many hours between rebuilds? Are you at about 3.6L, 24xx lbs and about 485 hp .. similar to the RSR?

MJR911

I bet Leh and Autometrics took those restrictors off the car that were mandated by pro racing!

kingleh

I think the cup car can so close to GT3rs times at sebring becuase the cup car takes the bumps muchbetter then the RS and the ABS really helps out on the bumpy tracks also. On a good smooth track a RS would be much faster.

Also when we got the car it had the Grand-Am restrictors, I raced with these at Roabling and got pulled by 05cup cars in 6th gear . So yeah we took them little bitty restrictors off. No my motor doesnt look like a RSR engine and isnt a rsr engine.

kingleh

Henzler ran a 2:15 rite out the box. Not 09-10s

Then his times lowerd. I was there all day thursday just hanging out and wathcing. Not driving.

he only got into 9s once and did a 2:09.9. During qualifying.

Henzler is a beast... he is indeed FAST.

I watched incar vid of him. Its nothing to crazy its just consistently being perfect throughout the whole corse. hit every apex, degree of slide was rite on, shifts perfect, brakes late etc.... rite on the dot every move he makes.

I dont even look at alex Job Racing times cause they have those cheater tires.

But yeah seems if i wouldnt have got held up by the racers group car a little a 7 mite have been possible. Wich i would have been super stoked about.

Rolo

Who cares! Those other guys are here sharing their video and talking with us....You're the man!!

ngoldrich

Leh,

Are you coming to MidOh to run the PCA race ? It's a great event.

Norm

kingleh

Thanks !




nah i think the next event im doing is CMP in the late fall.

Will mostly be doing Grand-Am stuff.

Sam N

Leh,

Thanks for posting and for the explanations. Informative and interesting. I sent the in-car to a colleague that ran the 24 hours of Daytona and he was impressed. Posts like this make Rennlist a great resource.

Regards,
Sam

ColorChange

Lah:

Can you please confirm if this is exactly what you are doing?

Here is what I think he is doing.

1. Let off the throttle and pull the car out of gear when the load is reduced.
2. If you do it right, the car slides out of gear without any "pop", grinding, or a big tug required.
3. As the car is now in neutral with the clutch out, blip the throttle. (We have skipped one cycle in the usual double clutch downshift.)
4. When you rev match, depress the clutch and slide the car into gear.
5. Release the clutch.
All quickly of course.

Larry Herman

Tim, I IM'd Leh yesterday & talked about that and other things. He is pressing in the clutch, blipping the throttle and changing gears, and letting the clutch back out again. Nothing fancier than that. He is just really good at it, and fast.

From a personal standpoint, I do not see any advantage in trying to slide the car out of gear. You have to press in the clutch anyway, and that is the slowest part of operation. And if you are a fraction off in your timing, you could bend the shifter, or jam it into the next gear & mess up the syncros.

I think that rowing down a close ratio gearbox does not require double-clutching because your "syncro speeds" are going to be close anyway. I double-clutch because I go down to the gear I want to be in, skipping as many as required. In that case, you really must speed up the input shaft via the double-clutch because the syncros will take forever to do that.

Also, if you jump from a sequential shifter, which you must hit every gear to a regular one, you are probably going to feel more at home rowing through all the gears.