adssoccer

im having a debate with my friends about double-clutching and drag racing. could someone explain to me what double clutching is, and why is it more beneficial than regular put in the clutch and shift?

Tom Delegram

Double De-clutching matches the engine RPMs to the gear selected. For example when down shifting from 4th to 3rd (in a perfect world), assume the engine RPM differential between gears was 1000 RPM's. You would do the following: Depress the clutch and move from 4th to neutral. Let the clutch out and blip the throttle so that the engine RPMs are now 1000 greater than they were in 4th gear (this is where the assumption comes into play, in reality it would be 1000 rpm's plus approx 100 because the engine and tranny will decelerate a little before you engage 3rd gear), depress the clutch and put it in 3rd. The main benefit is that the work usually done by the synchronizers (a wearable item in the tranny) is now done manually by matching engine and tranny RPMs. Another benefit will be gained when down shifting in this manner before or during a turn because you will not unsettle the suspension or ask you tires to do more work than they already are. As for on the drag circuit the only time it would be beneficial would be after the finish in the deceleration process. However, personally I would use the $100 dollar brakes to slow the car instead of the $5,000 motor!

jeremy

iTrader: (1)

double clutching is used to downshift when your synchros are bad, you don't have any, or are hard to shift into at the particular rpm. sequence is: off accelerator, clutch in, stick to nuetral, clutch out, blip throttle, clutch in, put into lower gear, clutch out. this all happens very fast. double clutching has no use in drag racing. sounds like a case of believing in the fast and the furious here. if you want i can scan the diagram that the haynes manual uses to show the sequence.

peejay

You only double clutch when drag racing when you try to get 3rd gear and get a big fat load of GRIND and you have to put it back in neutral, let out the clutch, then push the clutch back in and stuff it into gear. And at that point you're looking at a set of taillights in the opposite lane...

http://www.geocities.com/izzmus/pegs.html Look at the legs workin' in the bottom three pics... 3rd gear sucks, I hate 3rd gear...

edit: wrong url

jeremy

iTrader: (1)

hell no, you can still shove it into gear. it will stop grinding once in.

peejay

Shoving it hard into gear means it will get worse and worse each time you do it. Treat the shift **** like it's a raw egg - do not break the egg - and your transmission will still like you and shift nicely years down the road.

Here's a good explanation of what double clutching is and why it's needed on some cars: http://www.g-speed.com/pbh/double-clutch.html

inittab

What Tom said!

I've been double-clutching all my cars like this for years. It's easy on the tranny, it's easy on the clutch and makes high speed cornering a much smoother and faster operation. Plus it sounds cool! As we all know, the 1st Gen RX-7 is particularly sensitive to overstear. In my experience, double clutching into and through corners dramatically eases the transfer of weight and helps keep the rear tires firmly attached to the road.

Oh BTW, it's best to learn on a car with trashed synchros because it take a lot of practice to master and you'll have to do it out of necessity.

jeremy

iTrader: (1)

actually rev matching will work best for that. blipping the throttle before you let the clutch out. double clutching is takes too long. when i'd auotx or drive hard i'd just kill the bad synchro as you can't double clutch fast enough, even if you have it down pat. just too many things not to mention that you look like you're dancing a jig or doing the "gunshot" dance.

crankit

Back before most of you people were a thought we used to have to double clutch to go into first because the gears were not syncronized.

jeremy

iTrader: (1)

haha, that hasn't changed any. you couldn't go into first in my brand new wrx unless you were about stopped.

peejay

I've driven a non-synchro car before. Nobody else in the shop could shift in - I dropped right in and drove it no problem. It's nice the way the lever just falls right into place.

Also used to drive my Subaru clutchless... very easy with that car, somebody was very nice to the tranny It had only 180k on it... saved the tranny

Redwood

Did you read a Bob Bondurant book somewhere in your life? That's excatly what he says about shifting in a book I have by him (not a great book, but not too bad). I agree with this statement having now tried both ways.

peejay

Actually, I saw that at www.spdusa.com - has wonderful info on how to drive, as well as good info on modifying Imprezas.

Subarus are my other love... I prefer the "Loyale" bodystyle, but the Impreza is the same chassis with a different rear suspension, basically. Many things will swap between the two.

Redwood

That's a pretty sweet subaru site. I would have no problem driving one, but I only have room for two loves and they are the rotary and asian girls. Both very sexy.

error402

peejay the fist link you posted with the inside cockpit view of the first gen on the drag strip. That guy stole my smilie freshy thingie on the rear view mirror. LOL j/k

back on the subject: Double clutching is cake, I've been doing it on every manual car I've driven.

jeremy

iTrader: (1)

i never said it wasn't going to tear **** up. i just said if you shoved hard enough it would shut up. I NEVER NARKED ON NOBODY, I NEVER NARKED ON NOBODY.........

cletus

I usually only double clutch when putting around town and just want a lower gear, but not necessarily driving too quickly. Just to save the synchros for when I need them.

My guess about the drag racing thing goes right with whoever mentioned the fast and the furious. I laughed at that the first (and every time after) I saw that. ("Relax. I need NOS.") Especially with the cars they are driving. However, if you watch the beginning of Cannonball Run when they are driving the Countach, you can hear them blip the throttle between upshifts. Sounds cool in that car But I know nothing about how those cars are made so I'm not sure if it's a car with no syncros and the gears don't happen to line up well when driving it hard like they were or if they were just doing it to be cool in the movie. No clue.

I'm just bored at work so felt like responding

peejay

error402 - that's my good luck smiley... the third one I've had so far! <==-- looks just like that!

It's in the new car as well! Kinda like taking wood from the old house's fireplace into the new house's!

jeremy

iTrader: (1)

well the whole thing is to get your input shaft and output shaft rotating at the same speed. if you blip the throtle on an upshift the input shaft will be rotating faster then the output shaft which it was already faster when you started to shift. what you probably heard was the wimpy power shifting method where you keep your foot on the gas while changing gears using the clutch. it helps keep the engine momentem up and makes it super easy to bark second, sometimes third.

nimrodTT

I think some people on here might be confusing heal-toe downshifting with double-clutch downshifting.

REVHED

My motto is... if you can't find it, grind it!! j/k

Pele

iTrader: (28)

I can double clutch pretty well... I think. I figured out how to do it after wondering what to prolong the life of my clutch and synchros when I downshifted from 5th to 4th at highway speeds to accelerate from 80 MPH to pass the bastard who's doing just a hair under 80 in the left lane.

In my honda, shifting like that kicks my engine up about 1000-1500 RPM...

I clutch in, shift to neutral, hit the gas to slightly above where I know the tach will goto if I just shifted normally, then I clutch in, shift down, unclutch and floor it.

I've tried to heel-toe shift on exit ramps that bring me to another major highway with little merge room, so I can be up to around highway speeds as I pull out of the curve on the exit ramp.

The brake and gas pedals don't go together though. I can't blip the throttle when I have the brake down far enough to have slowed me down.

adssoccer

first of all, i really didn't trust anything in the fast and furious. my friend keeps telling me about this guy who really knows cars and always double-clutches when accelerating and dragging. everytime this guy is in my car he talks to me about it. it never seemed logical to me. so i WAS right that it isn't for dragging. and. . .

i am one of those. the last car i autoxed was a 95 vette, with all that torque, i never worried about downshifting. but with the seven, i want to be able to get down into 1st throught the hair-pins on the autox course. so, what is the difference between heel-toe and double-clutching? which is better/faster??
thanks guys!

jeremy

iTrader: (1)

heel-toe is faster, but 1st gear synchro is usually small and weak so unless you want to jam it into gear you'll probably have to double clutch.

0pistn

if you can't find'em, grind'em