ErnestSw

You're in 3rd gear and there's a red light ahead of you about half a block away. You downshift to 2nd and let the engine slow you down anticipating that you'll still be moving when the light changes and that you'll have to downshift anyway. The light changes as expected, you're still in the torque band, you haven't touched the brakes, you accelerate and all's well with the world.
I guess I'm the only one who's ever used the engine's torque to slow the car. My bad.

Marine Blue

Ernest I agree there are times when it really does make sense to downshift and use the engine but there are also instances when you are close to a light and it's turning red. Do you downshift only to take it down another gear and then get on the brakes or do you shift into neutral and hit the brakes?

ErnestSw

Brakes are cheaper and a LOT easier than clutches (ask me how I know).
My post was in response to those who "know" whether engine braking makes sense. The correct answer is yes----and no.

mark kibort

I know what you are talking about here, but the unskilled driver is basically unable to correct for most all non standard situation, and this goes for any car front or rear engine. The rear engine just makes things worse. Ive seen hundreds of turns with full throttle lift and correction for 911 drivers in the middle of very technical turns. certainly is not auto correct like our cars!

The main issue here is do you use the engine for braking on the street? there is a difference between leaving the car in gear and then slowing and downshifting if the rpms get low enough, and downshifting to get maximum engine braking. I think the point is why do a needless downshift as brakes do a better job at slowing. a skilled hand certainly doesnt need to double clutching to make a very smooth, low wear change of gears. anytime you use the clutch, you are creating some wear and there is also wear during the shifts on the transmission. working on matching rpms and do less high rpm braking and you will have a drive train that can last as long as the engine!

on the track, engine braking is such as small part of the decel, the gas is either on or off. (sometimes some feathering is needed on some turns) just like the brakes, its either full power or not at all. At laguna Seca for example, there is only one turn out of 11, where no brakes are used and compression braking is the only braking needed (turn 9 after the corkscrew). Otherwise, its all brakes or all gas, with very little time spent in between! I wouldnt want to be in neutral, as i mentioned, as engine connection to the rear wheels keeps the rears from locking up, basically like free ABS for the rears! its one of the BIG benefits for 4x4 race cars. threashold and trail braking is easier with the engine engaged to all 4 tires. much harder to lock up.

Mk



Mk

tomcat

Mark, how do you do that without slipping the clutch. That is, on the street when you are trying to be smooth. I'd rather slip it into neutral while reving the engine before dropping it into gear.

**My opinion** I would never brake in neutral. Brakes have to work that much harder. Unless you're in an uncontrolled spin.

mark kibort

you (I) rev the engine while the clutch is in. very easy to do. If you cant do this, it takes a little practice.

brakes do much of the work anyway. (point 2) with or without engine braking, makes very little difference. if i see a stop light, and i dont want to hear the glorious sound of a rpm blip downshift, i just coast down by putting the car in neutral and slowing by the brakes. not a big deal at ANY speed. brakes can produce near 1000hp, while engine braking is less than 60 at near highway speeds, 10-20 of this is just rolling friction!
mk

tomcat

Gotcha Mark. I guess you really don't have to disengage twice.

James-man

Agreed for the most part. For those that have not modified brake bias, you can feel the difference between Brakes-only braking and high RPM rev matching because there is some braking going on.

For me, it could be that I have felt the difference because I use much better brake pads in the front than on the back of the car. So clearly YMMV.

SwayBar

'Silly, no reason'? I think the following is much sillier:

So let's get this straight. You are advocating preserving a $100 throwout bearing, yet on the other hand, you state that it's 'silly' to preserve one's syncros in their very expensive 5-speed transmission?

Sure, one does not need to double-clutch just like one does not need to put their tranny in neutral with the clutch out at a stop light. Nonetheless, both are good practices for the sake of reliability, but one of them is much more costly to fix.

One would think that since you're concerned about a $100 bearing wearing out that you would be much more concerned about a part which cost much much more to fix. Each time you downshift without double-clutching, you're spooling up those syncros, heating them up and subsequently wearing them out over time. Fixing those syncros will prove to be infinitely more expensive to fix versus replacing a cheapo, easy to get to throwout bearing.

Additionally, since you're not a factory driver and must replace worn-out parts yourself, one would think that you would take much better care of such an important and expensive part of your car like the transmission, especially since those good 928 5-speeds keep getting harder to find.

On the bright-side, once those syncros expire, and they will without double-clutching on downshifts, at least you won't need to replace your throwout bearing too.

Jim bailey - 928 International

Wonder why second gear syncros are ALWAYS the first to go away on an early 5 speed and 4 th gear always looks good ! It is the DOWNSHIFTS . Engine braking is a throw back to the days when brakes sucked and race drivers HAD to use engine braking...Double clutching was manditory in the days before syncronizers I was quite proud of my self when I figured out how to get my 1947 Plymouth into first gear on the roll. Down shifting the VW bus into second without using the clutch also was quite fun . If you are on the street and see a red light turn red a block in front of you ease up on the gas pull the shifter into neutral no need for the clutch and coast with your foot off the throttle... no wear on clutch, trans or ENGINE . Then at the light when it is about to turn depress clutch count to three and move the shift lever slowly into first gear . But like the Ferrari 360 I saw on Harbor Blvd. as he came up behind 4-5 stopped cars stopped at a red light with cars on either side He downshifted reved it to about 4,000 RPM and burbled to a stop !!! It worked for him I LOOKED ! Modern transmissions the syncronizers assist in matching gear speeds to allow gears to mesh without grinding BUT the syncros work on friction and friction means wear no way around that. It all comes down to down shifting engine braking is FUN but it certainly is NOT needed and is NOT good for the car. As Mark Kibort points out car brakes are more efficient and much cheaper than engines ,transmissions, and clutches. At the track to go quickly you need to be back on the gas in the right gear through the corner because anytime you are turning you are using up energy and unless you are on the throttle you are slowing down in the corner. But I consider drag racing starts to be "car abuse" yet think road course racing is just using the car to it's full potential even though one hour of track time probably is more wear than 2,000 miles of street driving !

fabric

I had never heard this, you're ok to just pop it out of gear? This just seems like it wouldn't be good.

tomcat

I know the horse is dead by now, but...

How does leaving it in gear and coasting to a stop wear the clutch? i.e., I don't see the benefit of coasting in neutral to a stop. If anything it seems a little unsafe if you need to suddenly get out of the way of a minivan driver with a cell phone in the driver's ear (trying to be sensative to the sexes).

RyanPerrella

I wanted to post this.

I in no way meant to suggest that engine braking will slow the car anymore effectively then the front brakes. Our brakes are great and if i was racing my 928 i would slam the brakes every chance i get cause i know they could probably take it. But I do see the occasional use for engine braking, it dosent reduce your speed much, the 928 GT is a pretty close gearbox, as in ratios are fairly close, not a giant change in RPM going from one gear to the next, if anything you engine brake and go down 2 or 3 gears and slowly let the clutch out. I think its kinda fun, its something you cant do with an auto and i still dont think it accelerates any clutch wear to the point that its wasteful to do the occasional engine braking.

Obviously to stop fast use the brake pedal.

the flyin' scotsman

Jim said 'pull' the shifter into neutral.........ie don't use the clutch.

Safety of course takes presedence re. mini van drivers; not that I am one but when driving my truck the wife is always sticking things in my ear

Keeps you young.

tomcat

Malcom, hopefully your wife is doing it because she likes you.

Understood. But it seems whether you move it into neutral or just stay in gear while stopping, both methods wouldn't effect clutch wear. In fairness to Jim, he didn't explicitly say one method wears the clutch more than the other. Just said the method he described doesn't cause any wear. But then, either does the other. So things being the same, I'd leave it in gear so I can concentrate on protecting my ears canals.