Felix Wankel

Heel and toeing would have been a more appropriate term.

FuLLsMoKe

AH-HA! Great, LoL... That was hard enuf to learn, didn't wanna learn another technique that involves me not having my foot planted on the accelerator

hotty

ok, i am missing out on double clutching too.. wtf is it.. i mean i drive a semi illegally and u can power shift (no clutch) or you can double clutch.. anyway, there is no way i can logically explain how double clutching would help in a drag race.. someone EXPLAIN please and in DETAIL... thanx
Daryl

peejay

Power shifting uses the clutch, it's just whifting without letting your foot off the throttle.

My friend HAS TO double clutch his 1-2 shift, because his synchros are shot (probably from learning to drive clutchless ) So because his tranny's FUBARed the fast way to get into 2nd is to double-clutch.

It's amazing how people will watch a movie and then believe everything in it. Someone tried to make me watch it, I left the room after 5 minutes because it was just so stupid....

diabolical1

iTrader: (3)

well ... as someone rightfully pointed out earlier in this thread, it's all going to depend on the car and the person driving ...

it's hard to "drag race" using the advice of others because there are so many variables. giving advice for other forms of racing where techniques of driving are more universal is much more useful, but it just doesn't translate very well for drag racing.

anyway, here's my 2 cents ... just launch as low as it will take for you to hook up solidly (too low will bog, too high will spend time spinning tires)

your shift points should be as just before your engine starts to fall on its face ... depending on your setup, that can mean something as low as 6000 RPM. the only thing that i can say is powershifting is DEFINITELY the way to go in drag racing ...

i don't know what your "full" setup is, but if you're into drag racing, and you're pretty sure that you're not going to making any more MAJOR mods, then your focus should shift to suspension and mounting materials (eliminate as much of the rubber as you can tolerate!)

hope this helps

jeremy

iTrader: (1)

3,125.79263728363283682636833333 rpms. its all in the math.

unless you are running 60 series sidewalls, then use 2,823.56774382199666 rpms.

FuLLsMoKe

I'm curious... what movie was that?

And, when I powershift I always get a bit o grind when changing gears, specially from 2nd to 3rd. But I find that way gets me in the gear faster and with less loss of momentum... It's just a bit o grind but the noise scares people that don't know cars (kinda embarassing when you are with a girl)... Is that OK or am I doing somethin wrong?

JALVORD_2003_68

Let me settle this "double shifting" bullshit once and for all.
This goes back to late 40's or early 50's, back then trannies had **** for scyros, and add to that say a 2 speed rear end like wheat trucks use, and every time you shift it would grind the **** out of the gears. That is unless you shift into neutral, let the tranny slow down , and shift into your next hole.

Aside from really old wheat trucks, we have a 1947 International, i don't see why you would "double" clutch, usuall your tranny is needing new syncros.

I dont see how it could improve your dagstrip time because it take too dam long to do.

FYI: As redneck as this may sound, my daddy has been driving trucks for like dam near 25 years , so dont tell me i am wrong about this.

peejay

It's not that trannies had **** for synchros, it's that they had NO synchros.

FB + AWDDSM

Right, you also can double clutch a dog-box so not to hear the grind - but usually they're made strong enough to take the grind. Why else would you buy a dog box if it wern't strong enough.

FB + AWDDSM

Oh ya, the BEST way to find the shift point is to look at a dyno. Shift late enough that you'll drop to a rev point in the next gear that is still strong and making good power. But don't shift too late!

Hypothetically, lets say you have a U-shaped HP curve. @4500 RPMs you have 100hp, peak at 120 @ 5500 and back to 100 @ 6500. 75 at 7000, etc...
Now, you'll want to find the best point between 5500 & 6500 where it'll fall between 4500 & 5500 in the next gear. You'd use gear ratios to find this out.
Again in the imaginary engine, lets say your going 45mph @ 5500 in 2nd. by 6000, your at 60. Now at 45 in 3rd, you at 3500 rpms, so you know you're gonna have to shift later than 5500 in 2nd. 60 in 2nd leads to 5700 in 3rd, so then you've missed the power band all together!
By doing the math, you'd find that somewhere between 45 and 60 is the best mph point to shift at.

Believe it or not, thats the expanded cliff notes version

peejay

Cliff notes is shift so that the HP from the old gear is the same or as close as possible to the HP in the new gear.

Pedestrian X

sorry, about teh duble clutchin i was refering to autoX. double cluthching as far is i know is for when your down shifting. i dont see how it could help when dragging.. anyways for when your goin aroudn a tight corner or watever and ya need to down shift to get nice acceleration out of the corner so they down shift in the middle of the turn but if its tight and your car is pullign real hard you really dont wanna do anythign to upset the rear end grip the wheels have or watever or else it may cause you to loose traction and slide otu the rear end or what not so they double clutch to not upset the wheels and keep the mat soame moment em or watever

Felix Wankel

No, heel and toeing is to keep from upsetting the rear.

Double clutching is for trannies with no/bad synchronizers.

Sterling

...And so this is why I asked about the dashpot.

Jason Guthrie

By best you mean fastest since it's a drag race right? Seems HARD on the car to drop the clutch at high rpms especially when it's stock. For example, my driveshaft came loose and I am pretty sure it is from forced wheelspin fun...

Pedestrian X

sorry. they are quite similar though.

Sterling

No...They're not. That's the whole point.

Anyone can double (de)clutch.
It takes hours and hours of practice to learn to heel/toe.

brookscrb

If you have stock (non-hardened stationery gear), you run the risk of ruining the gear and locking up the engine at high RPM. At least that's what Atkins Rotary told me I did with the remanufactured engine I bought from them. It locked up and they wouldn't cover the failure under their warranty. I sware I never went past the red line and I never dropped the clutch, although I did like the feel at around 5-6000 RPM. I've got a '79 and to tell you the truth, I don't know if it has an over RPM buzzer or not - never heard it.

diabolical1

iTrader: (3)

just a quick question ...

is a "dog-box" the same thing as what we call a "crash box"?

peejay

That 6500 figure is a shift point not a launch RPM.

Launching is dependent on so many variables that it's impossible to tell since the variables include the driver, the clutch, the tires and their pressure, the gearing, the weather, the road surface.....

peejay

If I'm not mestaken, crash box means any non-syncronised transmission, although USUALLY it means the sliding-gear type. For example, early 50's Beetles had crashbox trannies (sliding-gear). Most 4-speed truck transmissions and 3-speed car transmissions have a sliding gear (crashbox) First gear.

Dog boxes are constant-mesh trannies like synchronised trannies, but instead of splines/side teeth on the slider and gear face and a synchronizer between the two to match their speed together, a dog box just has 5 to 7 or so big "dogs" or "lugs" and big windowes between them, that way speed difference doesn't matter, just shove it into gear and CLACK it's in gear right away.

Reverse gear on RX-7 trannies is kind of a hybrid. It's a constant-mesh gear like a synchro gear, and it uses side teeth, however there is no synchronizer ring or a cone for one to grip on. It's still non-synchronized but it it's constant-mesh. I thought that was kind of a weird way of doing it, since most trannies with non-synchro Reverse just slide and idler gear into and out of mesh in true crash box fashion.

Jeff20B

iTrader: (13)

Is that why I've got to double clutch before going into reverse on my SA tranny sometimes? It grinds a little if the internals are still spinning. I guess I've got to wait for it a little, huh?

peejay

You should only have to double-clutch to get into Reverse, if you're rolling backwards already. In that case yeah yud have to get things moving the right speed before it'd go into gear easily.

But if you're stopped, you should just be able to momentarily engage a forward gear (which stops the tranny's internals from rotating) then put it in reverse. if you just try to put it in reverse after it's been idling in neutral, then yes it will grind.

Felix Wankel

Or just push the clutch in and wait a few seconds.