mark kibort

Dave, its not me "saying so", its a fact of racing a car. you lift, you have compression braking.... its a fact of life. Its like holding your breath and thinking your lungs are not passing oxygen to your blood.

compression braking is a force, and a measurable one .... You just don't know because you haven't measured it as I have , or have thought about how many times you actually lift throttle over a lap. if you ever lift, you are using engine braking. Just because you are not aware of it, doesn't mean it's tnot here.

saying its bad to do, is irresponsible here, as someone might actually take you and Viking seriously. Wear is a fraction of what happens at WOT, based on the forces, and most of the reduced forces are only operating in the opposite direction, clearly within those components design use. the valve train doesn't know If there is negative or positive force on the drive train, or if you are at WOT or not. it just spins via the belt or chain. the clutch, it sees forces in both direction naturally, so its a non issue, especially with the reduced forces of decal vs WOT. to make such a claim that there is some kind of wear factor is a little irresponsible on your part.

If you disagree, I would certainly love to hear why.

Greg Smith

I haven't been on here for a year, I see absolutely nothing has changed.

mark kibort

Don't be a troll. there are enough here to call it, troll city.

ProCoach

Mark, the data does not support your supposition. It IS bad to do. It is not efficient, or a "skill execution" taught by any of the recognized (or less so) schools nor practiced by any pro I have been fortunate enough to capture data.

I'm with the opposing camp here, Mark. Viking and Dave...

mark kibort

I really don't understand how you can say that.

take a second and help me understand what you mean.

let me see ONE video where someone doesn't use engine braking. just one. Any video I've EVER seen of any pro or club racer, has the car in gear
and is decelerating. Even through the close ratio gears, the rpm is high, and so are the braking forces to the rear wheels. I don't know how you can deny this. very curious.

Are you advocating pulling the car out of gear from 130mph down to
70-80mph and braking in neutral before a downshift? if not, you are using engine braking whether you know it or not.

How is this bad? your seem to be like VR, Viking and the rest that always offer some statement, like "your wrong", and then offer no reasons for the comment and certainly "0" supporting information.
how is it wrong...... how can you even say that?

you don't have data to support anyone lifting off the throttle?? if you do, then you have engine braking. feathering the throttle will mitigate the engine braking effects. no gas, max effects. a little gas..... you get the idea. what part of this do you not agree with?

now, to the contrary, I instruct and make sure there is no "coasting" . you are always in gear, which means you are ready for anything that can happen to the car. if you ever upset the car and are out of gear, deceling, the chances are much less you will be able to control it, as well as have the right power available to accelerate effectively out of it. engine braking gives stability to the rear of the car, and provides the correct engine RPM to apply throttle when required .

again, post any video of someone that DOESNT use engine braking. (knowingly or not) just one! remember, (again), anytime you are off throttle, you are using engine braking, and doing so for a reason..... and the forces and effects are measurable and known

mark kibort

engine braking by Patrick long and I don't think he would have it any other way.

Veloce Raptor

Mark, what about that video suggests that he is not using the brakes??

J richard

This is absolutely correct, not sure why its being debated. Porsche pressure plates transfer about half the loads through straps on the sides of the plate between the sprung plate and the cover. The pic shows one that has been over stressed and has bent the strap. It is designed to work in tension not compression. Overloaded in compression the strap will bend until it folds/cracks/tears and one of two things happens; the strap tears off and spins around the inside of your bellhousing at 8000rpm essentially sawing it in half, or they all fail and the big peice of metal with the green arrow slides back and slams into the big peice of metal with the red arrow and they both go kaboom. This is generally a bad kind of kaboom which blows big chunks of your bellhousing out.... eliminating this is one of the benifits of the tilton style clutches...so yea Viking kinda knows what he's talking about....

mark kibort

Now hold on cowboy! are you suggesting that I've advocating not using the "real " brakes? If so, we are speaking different languages here.
Procoach? is this what you also think im saying?

if so, your response makes sense. no no no. engine braking adds to whatever braking you need to add to the situation, sometimes, in a lift, engine braking is all you need. I cant believe that you would think that I was advocating "no brakes". after all the threshold breaking talk!

to be clear..... im only referring to the rear brking force that the engine adds to the braking force the front brakes and rear brakes make during decel.

mark kibort

No, you clearly don't understand the amount of forces on the clutch pressure plate straps flat springs, or maybe you do, but are not familiar when those forces are exceeding the limits of the flat straps (springs). this doesn't happen under decel forces, and are not stretched under accel. it happens on a downshift of mismatching RPM. HUGE difference. the force under decel, clutch released, is a fraction of what can be generated on a mis RPM downshift. on a mis RPM downshift, the forces can be 2 x 3 that of WOT for most cars. (this is part of a discussion that compares the KE of the engine vs the car at speed generating forces on the driveline components..... including the clutch pressure plate)

so, he is NOT absolutely correct. decel forces are a normal part and well within the limits of the Porsche clutch. every time you let off the gas, you apply a negative force to the assembly, well within the design limits. again, there is NO racer around that doesn't use engine braking on decels, and during throttle lifts. AND , It doesn't hurt the pressure plate in any way.

so here is the net net of the design. those springs are not straps at all. they allow the pressure plate surface to retract with the release bearing. so, when reving the engine with the clutch in, the pressure plate surface is floating via the release springs. (flat springs).rev up, they stretch, on decal they compress. no big deal... but on a mis matched downforce and clutch slipping............ the force can be transferred to the springs before clutch engagement. BUT if the clutch pedal is released, and you have no clutch slipping ... there is no force on the springs. all the force is always transferred directly to the clutch discs relative to the surface of the pressure plate and flywheel. the straps (flat springs) are not involved in the torque on decel or accel.

the dual disc clutches have the same straps, on their intermediate plate. they support a lot of force but only on reving the engine with the clutch pedal pushed in. (it floats via the same straps or flat springs) once the pedal is released, the plate is sandwiched with 500lbs of force , against the plate, clutch discs, and flywheel. the clutch discs drive the driveshaft. no force is applied to the flat springs in this case, in accel or decal.

What you are looking at, is a negative force, miss matched RPM downshift. pure and simple. in no way, is a released clutch pedal put forces on those straps, or better called flat springs, either positive or negative. the springs are there to support the pressure plate surface as you rev the engine with the clutch pedal pushed to the floor. once the clutch pedal is released, the flatsprings are out of the picture.

as a note. look at your picture. the clutch cover is bolted to the flywheel the pressure plate is attached to the clutch cover via the springs. the pressure plate puts pressure on the clutch discs spinning between them, and synchronizes their speed via this pressure. all the force is from the main pressure plate spring fingers and clamps the discs to the flywheel. the flat springs are out of the equations once the pressure plate is pushing on the discs and flywheel.
Hard to visualize, but this is how It works. flat springs bend via quick RPM revs with the clutch in, or miss matched RPM downshifts.
The purpose of the flat springs is to retract the pressure plate surface from the disparate speed, spinning clutch discs which are tied to the transmission main input shaft.

333pg333

I think both parties are correct. Mark is technically correct in that of course there is some engine braking during coasting or maintenance throttle or just prior to blipping on downshifts. However nobody uses this compression deliberately to slow the vehicle. Well nobody that downshifts correctly. Potentially there is still some engine braking when you heel and toe if you don't get it perfectly too. Not everyone gets it perfect every time. I had the occasion to have no engine braking when the car would drop out of gear on fast sweepers many years ago. It's quite the eerie feeling just coasting through a corner at over 100mph with the engine idling and just ghosting through there with both hands tightly on the wheel. Definitely not a reassuring feeling.

ProCoach

Yes, that's what it sounded like you were saying.

Nobody said anything about "declutching," either...

mark kibort

well, everyone was saying, including you, that engine braking is bad. hurts the engine and is not taught. forget about when you apply the brakes, when you lift, you are using engine braking, plain and simple and the force is substantial. in 2nd, it can equal the total output of your rear brakes. ive measured it, and I can even show you the dyno runs
during decal with using the brakes, its a factor as well.... no where near as effective as the front brakes, but still a stabilizing factor in the rear of the car. It doesn't hurt the engine either, as I mentioned, the forces are only 1/3 of that of WOT. all components are designed for throttle lift, engine braking with no adverse wear.

mark kibort

that's like saying, no one uses rear brakes "deliberately". of course we do. as a driver, you should be familiar with all the forces acting on the car, because at some point in a race or lap, you might be called on to use one of those forces in a way that can best assist you. Yes, people use compression braking "deliberately". when you might ask? ever approach a kink at a race track. many of them don't require a brake stab, just a lift... the lift is engine braking. generally, getting around a tight hair pin turn, can require throttle/ and lift throttle. the lift throttle creates engine braking that can help rotate a tight car around a turn.
as you say, and many hear can attest, if your car drops out of gear.. (remember, I have that issue with 2nd right now if I don't physically hold it in gear). down the corkscrew, in neutral is not a good feeling to not have the rear planted via compression braking at the entrance . hard to create those rear braking forces any other way, unless you were really good with a hand brake. .

The point of all this, is to recognize the effects of engine braking. its substantial and is a force to consider when setting up bias settings. in most cases at high speed, engine braking is about 1/2 that of the rear brakes, and at the lower speeds it can equal. if you are at the edge of grip at high speed at the rear, at those slower speed entrances to curves, you might find yourself a little loose.

others are also chiming in that the forces are harder on the engine during engine braking and they are not. people are trusting others that are validating those that clearly don't understand the forces acting on some of the simplest components of the drivetrain, as gospel. This is a problem of the discussion right there.

333pg333

My understanding of the negatives associated through the term 'engine braking' were due to mistimed downshifts while heel/toeing or even not blipping at all and relying on engine braking to help slow you more than the brakes. That is probably what most people are objecting to in this thread. We've all seen it where someone basically just puts the car in the next lowest gear and releases the clutch whereby the engine revs overly high and sometimes leads to the rear tyres chirping (rwd car).

Of course there is some engagement of the engine during off throttle / in gear moments. We don't knowingly think 'I must use engine braking through this upcoming corner'. We just do it. By balancing the car on the throttle we are using the compression of the motor at these moments. If you want to term that 'engine braking' for the sake of argument, just preface this before beginning discussion and this will save you some R.S.I.