Engine braking
Discussion
Just read a comment by the guru Steve Heath saying that ideally only the brakes should be used for stopping in TVRs rather than changing down a gear and using the engine plus a little bit of the brakes. Just wondered if this is definitely what people recommend for safe, efficient stopping.....? Does this just apply to TIVs (i.e. can't the engines take it?
)Personally I'd happily use a rover lump to help braking - especially when driving swiftly on roads (but not on the limit). I wouldnt use an AJP for engine braking , I dont think that it is really suited to that. Not becuase of fragility but because that it is light fly wheel, peaky etc
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Just read a comment by the guru Steve Heath saying that ideally only the brakes should be used for stopping in TVRs rather than changing down a gear and using the engine plus a little bit of the brakes. Just wondered if this is definitely what people recommend for safe, efficient stopping.....? Does this just apply to TIVs (i.e. can't the engines take it?
Hmm. Change down a gear, upping the revs to match the new gear, and then use engine braking? Sounds an ideal setup for lift-off oversteer to me.
I'll await the words of the more experienced...
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Forgive my ignorance, but when does lifting off turn into engine braking ?
When you lift off to the stage where insufficient fuel is getting to the engine to maintain revs, and drive, at the wheels, the wheels start to drive the engine. The more you have lifted off, the less the engine is driving itself, and the more the wheels are driving the engine. This takes power, and hence has a braking effect.
When the force required from the wheels to keep the engine turning exceeds the gripping force of the wheels on the road - water, slippery surface, or cornering - then the wheels can lock up - resulting in lift-off oversteer.
The problem with Rover V8 engined TVRs is the huge amount of engine braking, combined with the relatively light body weight.
A bit of eninge braking - say slowing from X mph, to X minus 10 mph for a corner is OK, and can be gentler than braking in some instances - but changing down and matching at around 4 to 5000 rpm, and then lifting off totally will undoubtedly lock the rear wheels.
Because engine braking only works on the rear axle, which becomes 'unloaded' under braking, it is very easy to over do it.
That said, any braking - eningine or conventional - should be done BEFORE turning in to the corner, unless your name's Michael Schumacher
A bit of eninge braking - say slowing from X mph, to X minus 10 mph for a corner is OK, and can be gentler than braking in some instances - but changing down and matching at around 4 to 5000 rpm, and then lifting off totally will undoubtedly lock the rear wheels.
Because engine braking only works on the rear axle, which becomes 'unloaded' under braking, it is very easy to over do it.
That said, any braking - eningine or conventional - should be done BEFORE turning in to the corner, unless your name's Michael Schumacher
That is certainly the cost recommendation. However I was taught(rally course, so slightly different) that engine braking was more controlled.
I believe that engine braking can also prevent total lock up, since the engine, while absorbing power and thus slowing the car/drivetrain/wheels also has a large amount of Momentum, which prefers not to be slowed too quickly. This would surely provide a smoother braking action under extreme end-of-a-long-straight-into-corner type braking.
Could be wrong though, but it certainly works when braking hard on mud and slate in a Welsh forest.
Steve
>> Edited by madasahatter on Tuesday 13th August 15:05
I believe that engine braking can also prevent total lock up, since the engine, while absorbing power and thus slowing the car/drivetrain/wheels also has a large amount of Momentum, which prefers not to be slowed too quickly. This would surely provide a smoother braking action under extreme end-of-a-long-straight-into-corner type braking.
Could be wrong though, but it certainly works when braking hard on mud and slate in a Welsh forest.
Steve
>> Edited by madasahatter on Tuesday 13th August 15:05
Heel toeing will be good to ensure that if you should need to change down gear mid-bend that the "jerk" sent through the drivetrain as the clutch tries to match the engine speed through gearbox to the wheel speed doesn't induce temporary lockup, or unbalance the car (nose diving).
Plotless: You point about the 4wd thing is right. I was driving a rwd Escort at the time. I suppose I always think about what a car feels like when freewheeling (not good IMHO), and extrapolate that to the point that the closer that the gear and engine drag on the car matches the speed that the wheels are going round, then the more balanced the car will be. Engine braking seems to balance the car more to me.
I have yet to see (hear) a racing driving who doesn't change down under heavy braking, and thus that must be the best way to do it
Plotless: You point about the 4wd thing is right. I was driving a rwd Escort at the time. I suppose I always think about what a car feels like when freewheeling (not good IMHO), and extrapolate that to the point that the closer that the gear and engine drag on the car matches the speed that the wheels are going round, then the more balanced the car will be. Engine braking seems to balance the car more to me.
I have yet to see (hear) a racing driving who doesn't change down under heavy braking, and thus that must be the best way to do it
I have yet to see (hear) a racing driving who doesn't change down under heavy braking, and thus that must be the best way to do it
I think you might find they are not using engine braking but matching the right gear to the speed of the car so that when they come off the brakes they are in the right gear to accelerate out.
I guess that is one reason for it, but why not jump gears?
If they are matching the engine speed to their wheel speed, then surely they are engine braking?
Sorry if I sound Anal. I am just interested in the subject. I very much doubt I am anything but an equal in terms of driver skill to anyone else on this site.
Just feels right, that's all.
If they are matching the engine speed to their wheel speed, then surely they are engine braking?
Sorry if I sound Anal. I am just interested in the subject. I very much doubt I am anything but an equal in terms of driver skill to anyone else on this site.
Just feels right, that's all.
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Sorry if I sound Anal. I am just interested in the subject. I very much doubt I am anything but an equal in terms of driver skill to anyone else on this site.
Just feels right, that's all.
try looking atwww.motor-tech.co.uk/braking.htm
I got trained (IAM) not to bother changing down when braking..but to block change to the most appropriate gear AFTER the braking and BEFORE turn-in to the corner.
On a track that takes up valuable extra time that just doesn't matter on the road.
Hence Heel and Toe - allows you to be braking at the full potential of the braking system and grip without adding additional engine braking by changing down DURING the brake and causing the rear wheels to lock up thereby....since braking and changing down to the proper corner exit gear are overlapped it all happens faster.
Not to mention sounding absolutely brilliant!
You can hear the car "hating it" (and wearing out the clutch) changing down whilst braking unless you heel'n'toe and match engine revs to road speed prior to letting up the clutch...IMHO
I only heel and toe on the road to practice for the track. In general road driving I just wait until after I'm off the brakes to change gear...
On a track that takes up valuable extra time that just doesn't matter on the road.
Hence Heel and Toe - allows you to be braking at the full potential of the braking system and grip without adding additional engine braking by changing down DURING the brake and causing the rear wheels to lock up thereby....since braking and changing down to the proper corner exit gear are overlapped it all happens faster.
Not to mention sounding absolutely brilliant!
You can hear the car "hating it" (and wearing out the clutch) changing down whilst braking unless you heel'n'toe and match engine revs to road speed prior to letting up the clutch...IMHO
I only heel and toe on the road to practice for the track. In general road driving I just wait until after I'm off the brakes to change gear...
I'm no expert either, but the last time at Zolder circuit I experienced the difference between heel and toe and not-heel and toe.
When pushing hard, revving high and braking late, using heel and toe prevented the rear wheels from locking or the rear feeling light-ish. It stayed planted on the road.
When I got a bit tired, I was too lazy to heel and toe a few times and immediately the car felt lighter and the rears started sliding a little. It did vary per turn a bit.
This is for a (Griff) 500 which is very torquey. I can imagine that for a multi valve Speed 6 it is different but I don't know.
When pushing hard, revving high and braking late, using heel and toe prevented the rear wheels from locking or the rear feeling light-ish. It stayed planted on the road.
When I got a bit tired, I was too lazy to heel and toe a few times and immediately the car felt lighter and the rears started sliding a little. It did vary per turn a bit.
This is for a (Griff) 500 which is very torquey. I can imagine that for a multi valve Speed 6 it is different but I don't know.
Interesting link.
Found this one as well, where "Tiff and Friends" talk about it engine braking. Nobody seems to have a direct answer!!
I'm afraid you will have to rebuild the URL below - doesn't quite post properly.
http://groups.google.com/groups?q=engine+braking+race&hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=7uhjij%24421%241%40nnrp1.deja.com&rnum=2
Found this one as well, where "Tiff and Friends" talk about it engine braking. Nobody seems to have a direct answer!!
I'm afraid you will have to rebuild the URL below - doesn't quite post properly.
http://groups.google.com/groups?q=engine+braking+race&hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=7uhjij%24421%241%40nnrp1.deja.com&rnum=2
There's a good book and video called roadcraft, it's produced by the police and is used to train their pursuit drivers. In this book they have a thing called the system. Basically there are 4 things you can do to a car. Accelerate, brake, turn, change gear. They say you should do these one at a time. So when slowing down, brake until you reach the right speed for the hazard(corner) then stick it into the matching gear, that way you have both hands on the wheel while braking, then both hands on the wheel for turning. I went out with ride-drive and they did the same.
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