mazdaspeedwest

How does that go now?

aaaaahhhhhh, ok i get it....

oregano

your toe is more sensative, and you can use that sensitivity to keep your tires from locking up. the gas does not require this sensitivity, only proper timing. my problem is that my heel gets stuck on the side of the centre console

mazdaspeedwest

ya thats more like what i do too, i've been practicing in our lovely Cali traffic..... aftermarket pedals help too, as the gas pedal will have a tab on the brake pedal side. This helps me perfectly, since when i come home at night the system is at FULL VOLUME (stress relief) and the RPMs will dip at a dead stop. So i have my foot half on each pedal and can keep the RPMs at 1000 to keep from dipping....ya i know, time for a bigger alternator, but eh, won't make me go faster so it's not a priority

It's kind of a roll over effect too, hard to explain, but hey do what ever works for you.

Eddiewould

Umm is it just me or is the point being missed in this thread?

Well its my belief that engine breaking doesn't really do anything to the clutch

the only thing engine breaking will really affect are the syncho's in the gearbox. And this wont happen unless you're doing some heniously different revs from one gear to another.

my $0.02

JJB

the way that it is taught at performance driving schools is to use the ball of your foot on the brake (this still provides a good amount of force should you need it) and then you use the heel of your foot to blip the accelerator.

Here's a good on-line article on it.

David

That's a nice site.

turboge

I should have a couple video's with a little heel/toe shifting up on the web shortly. I just pulled them off my camera along with a quick little run through the mountains in the Spec V.

Davard

Clearing up a few things here.

Engine braking does so little that it's not very useful for slowing a car. It was done in the past because brakes were not very good (rear mechanical drums, hand-lever operated), engines were huge and full of friction. Nowadays, brakes on cars are so good that downshifting to slow a car is pointless.

Also, most of the braking is from friction, not compression. And what isn't friction is actually vacuum braking, as the pistons try to pull air past the closed throttle plate.

Now, downshifting for performance driving, or when entering a corner, is something different. Here, it's done so that you are in the correct gear when you exit a corner.

The point of heel-toe downshifting, or rev-matching downshifts, is that it reduces the upset to the car (don't believe me, try downshifting a RWD car without rev-matching and watch the lightly loaded rear wheels lock up. It will also reduce wear on the synchros.

And, diesels engines produce almost no compression/vacuum braking, because they have no throttle plate. That noise you hear diesels making is from a device called a Jake Brake (generically). This acts on the valves to produce nearly 100% of the engine's output in braking force (A typical 400hp diesel engine might have 350-400hp of braking with a Jake Brake). Diesel pickups often use an aftermarket exhaust brake (a valve in the exhaust system that can be closed off) to perform a similar function. Semis also use things like hydraulic retarders to slow them down, but these generate enormous amounts of heat.

mazdaspeedwest

Diesels also use an exhaust brake, or is that the Jake Brake your refering to?

Davard

Big rigs use an exhaust brake, but it is intregrated into the head (controlling the exhaust valves) rather than on the exhaust pipe itself, as is fitted to pickup diesels.

For how it works, try How stuff works