Acceleration technique
Discussion
Just thought I would get your thoughts on the quickest way to accelerate the Chimaera. Figures are approx.
For a 4.5L Max torque is at around 4750rpm, Max power is achieved at around 5500rpm and Max revs are at around 6250rpm.
Now the torque falls off quite noticably above 5000rpm. Does it therefore make sense to change up at max power (5500rpm), and therefore find yourself back at around 4750rpm - the highest torque level for the next gear (and keep this going all through the gears)?
Or should you simply rev all the way to the red line (6250rpm) in each gear before changing down?
Another interesting question is how quickly to press the accelerator pedal. If you floor it straight away, does this provide faster acceleration than pressing it quickly but progressively.
Finally, from a standing start, is it really best to rev to max torque level and dump the clutch? How long does it take you clutch to burn out with this treatment?
For a 4.5L Max torque is at around 4750rpm, Max power is achieved at around 5500rpm and Max revs are at around 6250rpm.
Now the torque falls off quite noticably above 5000rpm. Does it therefore make sense to change up at max power (5500rpm), and therefore find yourself back at around 4750rpm - the highest torque level for the next gear (and keep this going all through the gears)?
Or should you simply rev all the way to the red line (6250rpm) in each gear before changing down?
Another interesting question is how quickly to press the accelerator pedal. If you floor it straight away, does this provide faster acceleration than pressing it quickly but progressively.
Finally, from a standing start, is it really best to rev to max torque level and dump the clutch? How long does it take you clutch to burn out with this treatment?
I've always been told that there is no point in exceeding the max power... what's the point? Pick another gear and get another surge forward. Personally, I tend to use the max torque (or thereabouts) for my shifts when pressing on. Using the figures you've given, I'd probably shift at 5000rpm.
Dumping the clutch at max torque? er... that'll probably do the car no favours. Again, I was always taught to be smooth and progressive in all movements - whether accelerating or braking. To move off sharpish, I'd dial in a few more revs than usual, and bring the clutch in - always trying to be on the limit of the tyres grip, but not exceeding it.
I was lucky enough to get a lift across a circuit from one D. Hill several years back, and was amazed at how smooth the man was at everything... it was so unhurried, yet the car wasn't exactly hanging around.
Dumping the clutch at max torque? er... that'll probably do the car no favours. Again, I was always taught to be smooth and progressive in all movements - whether accelerating or braking. To move off sharpish, I'd dial in a few more revs than usual, and bring the clutch in - always trying to be on the limit of the tyres grip, but not exceeding it.
I was lucky enough to get a lift across a circuit from one D. Hill several years back, and was amazed at how smooth the man was at everything... it was so unhurried, yet the car wasn't exactly hanging around.
quote:
Now the torque falls off quite noticably above 5000rpm. Does it therefore make sense to change up at max power (5500rpm), and therefore find yourself back at around 4750rpm - the highest torque level for the next gear (and keep this going all through the gears)?
Or should you simply rev all the way to the red line (6250rpm) in each gear before changing down?
I would change up at the point where the torque curve going down in the lower gear reaches the same level as the torque curve coming up in the higher gear - i.e. change up at about 5250, ending up somewhere below 4500 in the higher gear. The only reason to go much higher is because you've run out of gears (!) or because you know you're about to brake and slow down again, and it's not worth (briefly) changing up and then down.
Neil
Disclaimer: Based on my extensive experience as a novice sprinter, 6 events into my first season - there are wiser (piston)heads around with weightier advice
quote:IIRC you want to get about 15% wheelspin. Try starting at 4000rpm & bringing the clutch in smoothly (don't dump it as you would with a 4WD car)
I'd dial in a few more revs than usual, and bring the clutch in - always trying to be on the limit of the tyres grip, but not exceeding it.
This isn't a recipe for clutch longevity, but it should be fairly quick off the line...
cheers,
Craig
quote:The 5250 is a red herring - this is where power quoted in bhp and torque in lbft just happen to be the same (power = torque * rpm)
I would change up at the point where the torque curve going down in the lower gear reaches the same level as the torque curve coming up in the higher gear - i.e. change up at about 5250, ending up somewhere below 4500 in the higher gear. The only reason to go much higher is because you've run out of gears (!) or because you know you're about to brake and slow down again, and it's not worth (briefly) changing up and then down.
Neil
You basically need to work out the actual effective torque at the wheels (or propshaft), which you can do from the gear ratios (ignore final drive). You then change up where the torque has dropped off sufficiently that changing up produces more *effective torque at the wheels*. If the gearing isn't very close, this can mean that for optimum acceleration you would go beyond peak power, because that might still have more effective torque.
However, it isn't nice regularly going beyond peak power for the large Rover V8 road engine, so that's as good a place as any to change up.
If you want a good example of seeing the effective torque graphs, get a copy of Bike magazine; they now plot road effective torque (i.e. the acceleration you feel) for each gear, in addition to a simple dyno plot. This clearly shows the higher geared bikes with more power potentially losing out on acceleration up to 120mph to more sensibly road geared bikes.
danny
dannyIt has the right idea. I did a detailed model of theoretical acceleration for my hybrid single seat racing car (0-60mph in 2.2s - rock and roll!) for my MEng thesis (so it was pretty thorough before anyone picks up on the 'theoretical' bit!) and your key measurement is the 'motive force' generated.
Acceleration is dominated by torque at low speeds and power at high speeds. If you take into account the power and torque curves of the engine (minus the power sapping effect of the transmission), the gear selected, the final drive ratio and traction (a massively complex function of tyre/surface friction coefficient, tyre pressure, weight over wheels including weight transfer under acceleration, degree of slip, etc.) you can produce a good theoretical 'perfect' acceleration curve for a given surface condition, this will include an 'optimum' number of revs to use to accelerate off the line with maximum effect. However, seeing the perfect curve on a computer and actually producing one with your two feet is a very different thing.
Automatic launch control uses accelerometers mounted on the wheels to detect wheelspin rather than attempting to follow some kind of pre-determined acceleration curve, not least because the curve changes every time one of the variables mentioned above changes (i.e. it rains, you change your tyres, your on a different type of tarmac, etc.)
So, after all that useless background information, what's my conclusion.... Well, I'm afraid it's simply 'Go to a test track with some timing gear and find out what works best for you and your car'. Sorry it's not very helpful but it's the best way IMO.
roadsweeper.
Acceleration is dominated by torque at low speeds and power at high speeds. If you take into account the power and torque curves of the engine (minus the power sapping effect of the transmission), the gear selected, the final drive ratio and traction (a massively complex function of tyre/surface friction coefficient, tyre pressure, weight over wheels including weight transfer under acceleration, degree of slip, etc.) you can produce a good theoretical 'perfect' acceleration curve for a given surface condition, this will include an 'optimum' number of revs to use to accelerate off the line with maximum effect. However, seeing the perfect curve on a computer and actually producing one with your two feet is a very different thing.
Automatic launch control uses accelerometers mounted on the wheels to detect wheelspin rather than attempting to follow some kind of pre-determined acceleration curve, not least because the curve changes every time one of the variables mentioned above changes (i.e. it rains, you change your tyres, your on a different type of tarmac, etc.)
So, after all that useless background information, what's my conclusion.... Well, I'm afraid it's simply 'Go to a test track with some timing gear and find out what works best for you and your car'. Sorry it's not very helpful but it's the best way IMO.
roadsweeper.
Traction control doesn'r use accelerometers. They use wheel speed sensors i.e. count pulses as the wheels rotate so that they can identify any mismatch in wheel speed. There's an article on the Racelogic system on my website if you are interested.
If you want to car to accelerate... rev it. If you can go a few hundred revs more than someone else, then the car will be quicker. If I accelerate and change early at just over 5000, the car is noticeably slower. At 6 and a bit it flies. Mind you a bad gear change can ruin all the gains or failing to get full throttle can loose all the gains.
Steve
If you want to car to accelerate... rev it. If you can go a few hundred revs more than someone else, then the car will be quicker. If I accelerate and change early at just over 5000, the car is noticeably slower. At 6 and a bit it flies. Mind you a bad gear change can ruin all the gains or failing to get full throttle can loose all the gains.
Steve
quote:Lose not loose!
If you want to car to accelerate... rev it. If you can go a few hundred revs more than someone else, then the car will be quicker. If I accelerate and change early at just over 5000, the car is noticeably slower. At 6 and a bit it flies. Mind you a bad gear change can ruin all the gains or failing to get full throttle can loose all the gains.
Anyway, Steve - that's only because your car has peak power close to the limiter. For engines which rev quite far beyond peak power, and don't have as close gearing, that's NOT true. Though admittedly more a common phenomenon no motorbike engines.
Loose/lost you know what I mean. I'll use mislaid next time!
I've sprinted cars with max torque/power figures all over the place including various engine configurations in the 390 where the peaks were similar to that on a Chimaera. The question is "Does the time it takes for the engine to go from 5500 rpm to 6000 rpm and the car to accelerate between those two corresponding speeds shorter than the time taken in the next gear to go between those two speeds?"
In my experience and years of data logs, the answer is often yes. It can often only be a few tenths but it is significant. The trick is to know how many revs above the peak can you go. The engine doesn't develop full power and 1 rpm over stop. The higher the revs that you can take, the power/torque there will be when the gear change is made. Takes a lot of practice and there are a lot of variables but it can shorten those times.
I agree that having peaks high up the band is an advantage, the Griff is at 6033 rpm and the 520 is at 6300 ish but the rev range is there to be used. I am not advocating overrevving but if you want the best acceleration, consider burying that throttle!
Steve
I've sprinted cars with max torque/power figures all over the place including various engine configurations in the 390 where the peaks were similar to that on a Chimaera. The question is "Does the time it takes for the engine to go from 5500 rpm to 6000 rpm and the car to accelerate between those two corresponding speeds shorter than the time taken in the next gear to go between those two speeds?"
In my experience and years of data logs, the answer is often yes. It can often only be a few tenths but it is significant. The trick is to know how many revs above the peak can you go. The engine doesn't develop full power and 1 rpm over stop. The higher the revs that you can take, the power/torque there will be when the gear change is made. Takes a lot of practice and there are a lot of variables but it can shorten those times.
I agree that having peaks high up the band is an advantage, the Griff is at 6033 rpm and the 520 is at 6300 ish but the rev range is there to be used. I am not advocating overrevving but if you want the best acceleration, consider burying that throttle!
Steve
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