Santapod on 14th ??
Discussion
spitfire4v8 said:
your limiter is at 6500rpm so change around 6400 if you can.
If you want you can have a beeper sound when it's time to change gear.
I await to see if much acceleration is gained through the gears running this high up the revs.If you want you can have a beeper sound when it's time to change gear.
Personally i dont think theres any need in exceeding the peak power point but will be happy to be proved wrong.
That's what's bothering me - the interaction of BHP and torque, and it applies on track days too, especially when trying to stay ahead of Mr 5.5.
Roughly speaking, with standard T5 and BTR diff, I am at 5200 rpm in third gear at 80mph. Changing to 4th gear at that point would drop my revs to 4000, which is my peak torque, even though it is below my peak BHP. So my question is should I change at 5200, or say 5900 as Derek suggests - which would be 4600 in 4th.
Graph attached so you can see how my bhp and torque relate
Roughly speaking, with standard T5 and BTR diff, I am at 5200 rpm in third gear at 80mph. Changing to 4th gear at that point would drop my revs to 4000, which is my peak torque, even though it is below my peak BHP. So my question is should I change at 5200, or say 5900 as Derek suggests - which would be 4600 in 4th.
Graph attached so you can see how my bhp and torque relate
Forget the torque figures they're meaningless in trying to determine the performance of a car. You want to be riding the peak power hump of the graph.
This excellent web page tells you everything you need to know
http://craig.backfire.ca/pages/autos/horsepower
website conclusion:
Conclusion
In order to quickly accelerate a vehicle, the engine must be able to make a large force at the speed that the vehicle is traveling. The amount of power determines the force that the engine can create at a given speed, whether it is a very low speed or a very high speed. It does not matter if the engine makes power by revving high or making a lot of torque, because drivetrain gearing can be used to adjust the torque and revs proportionally.
This excellent web page tells you everything you need to know
http://craig.backfire.ca/pages/autos/horsepower
website conclusion:
Conclusion
In order to quickly accelerate a vehicle, the engine must be able to make a large force at the speed that the vehicle is traveling. The amount of power determines the force that the engine can create at a given speed, whether it is a very low speed or a very high speed. It does not matter if the engine makes power by revving high or making a lot of torque, because drivetrain gearing can be used to adjust the torque and revs proportionally.
Edited by spitfire4v8 on Thursday 18th September 17:09
All i know is despite what a rolling road graph tells you that when you are on the strip you can feel the acceleration drop off when you reach a certain rpm from the seat of your pants. No point trying to squeeze more rpm if the engines getting reluctant. May as well grab the next gear sharpish and get accelerating again.
All comes down to practice on the dragstrip and finding the sweet spot in each gear.
I never push first and always short shift into second. Works for me anyway.
All cars have different demands due to many variables such as traction available, gear ratios, torque, peak power etc etc
All comes down to practice on the dragstrip and finding the sweet spot in each gear.
I never push first and always short shift into second. Works for me anyway.
All cars have different demands due to many variables such as traction available, gear ratios, torque, peak power etc etc
QBee said:
That's what's bothering me - the interaction of BHP and torque, and it applies on track days too, especially when trying to stay ahead of Mr 5.5.
Roughly speaking, with standard T5 and BTR diff, I am at 5200 rpm in third gear at 80mph. Changing to 4th gear at that point would drop my revs to 4000, which is my peak torque, even though it is below my peak BHP. So my question is should I change at 5200, or say 5900 as Derek suggests - which would be 4600 in 4th.
Graph attached so you can see how my bhp and torque relate
ALL graphs should cross at 5252 rpm. Unless the scale on one side doesn't start from the same point as the other side (usually zero). Watch out for that when using a graph produced by a rolling road company. It isn't a 'fiddle' really, it just moves the crossing point. It's because torque and power are a function of each other. For the long version:Roughly speaking, with standard T5 and BTR diff, I am at 5200 rpm in third gear at 80mph. Changing to 4th gear at that point would drop my revs to 4000, which is my peak torque, even though it is below my peak BHP. So my question is should I change at 5200, or say 5900 as Derek suggests - which would be 4600 in 4th.
Graph attached so you can see how my bhp and torque relate
http://www.howstuffworks.com/question622.htm
By taking an engine close to it's redline, I'd expect you should be close to max power in the next gear up, as you say.
Edited by ianwayne on Thursday 18th September 17:25
Useful tool here
http://www.gearboxman.co.uk/inforatios.html
Heres an example for my car. I have standard gearbox ratios but note most will want to change the tyre size and the final drive (diff) ratio to suit.
http://www.gearboxman.co.uk/inforatios.html
Heres an example for my car. I have standard gearbox ratios but note most will want to change the tyre size and the final drive (diff) ratio to suit.
db484bhpv8 said:
All i know is despite what a rolling road graph tells you that when you are on the strip you can feel the acceleration drop off when you reach a certain rpm from the seat of your pants. No point trying to squeeze more rpm if the engines getting reluctant. May as well grab the next gear sharpish and get accelerating again.
All comes down to practice on the dragstrip and finding the sweet spot in each gear.
I never push first and always short shift into second. Works for me anyway.
All cars have different demands due to many variables such as traction available, gear ratios, torque, peak power etc etc
You can work it out if you have a datalogger that plots rate of acceleration .. change gear only when the rate of acceleration in the next highest gear exceeds the current rate of acceleration in the current gear.All comes down to practice on the dragstrip and finding the sweet spot in each gear.
I never push first and always short shift into second. Works for me anyway.
All cars have different demands due to many variables such as traction available, gear ratios, torque, peak power etc etc
Whilstever you are not traction limited this is usually a point well past peak power (ie dont change gear until the rate of drop off of power isn't yet compromising acceleration more than the loss of power times higher gear ratio of the next gear).
Anthony can prove his own argument himself though .. go out and do a full bore acceleration run but change up at say 4500rpm so you're riding the hump of the torque curve .. then do another run but change up at say 6200rpm so you're riding the hump of the power curve.
Come back and tell us which gave the quickest acceleration ..
spitfire4v8 said:
You can work it out if you have a datalogger that plots rate of acceleration .. change gear only when the rate of acceleration in the next highest gear exceeds the current rate of acceleration in the current gear.
Whilstever you are not traction limited this is usually a point well past peak power (ie dont change gear until the rate of drop off of power isn't yet compromising acceleration more than the loss of power times higher gear ratio of the next gear).
Anthony can prove his own argument himself though .. go out and do a full bore acceleration run but change up at say 4500rpm so you're riding the hump of the torque curve .. then do another run but change up at say 6200rpm so you're riding the hump of the power curve.
Come back and tell us which gave the quickest acceleration ..
Obviously 6200 will beat 4500.Whilstever you are not traction limited this is usually a point well past peak power (ie dont change gear until the rate of drop off of power isn't yet compromising acceleration more than the loss of power times higher gear ratio of the next gear).
Anthony can prove his own argument himself though .. go out and do a full bore acceleration run but change up at say 4500rpm so you're riding the hump of the torque curve .. then do another run but change up at say 6200rpm so you're riding the hump of the power curve.
Come back and tell us which gave the quickest acceleration ..
But will 6200 beat 5900? I honestly believe in Anthony's case it would make no difference. In fact going by his power curve i would wager 5900 for the win.
Only one way to settle this.... RACE!
I think we concur really.
Well obviously 300rpm apart is very close, you'd only know with repeated testing, and the optimum change up point will differ as you go up through the gears .. but the point I'm making is that Anthony was asking about changing gear so he's closer to riding the torque peak than the power peak, but that it's the power that's important, so you might aw well ride it out to the limiter and take advantage of the much higher power output in the next gear.
Plotting the acceleration curve through each gear will give you the definitive answer though.
Anthony likes his track days and sprints at curborough though .. it's in his interest to find out and do the test himself for his particular car / engine?
Anyway, the answer is always power!
Plotting the acceleration curve through each gear will give you the definitive answer though.
Anthony likes his track days and sprints at curborough though .. it's in his interest to find out and do the test himself for his particular car / engine?
Anyway, the answer is always power!
Thanks guys, this discussion is excellent and much appreciated. I will be following Mr 5.5 on a track day very soon, so will do the tests you suggest on the straights at Snetterton or Cadwell Park and report back. Clearly I will be able to measure my speed in each case by the gap to Mr Consistent, or by my terminal velocity before braking into the next corner.
In my Chim 400 days I would have had no doubt - power every time. I only asked the question because now I have a very torquey 500 and it feels more capable at lower revs.
I do in fact rev it to around 6000 rpm on track days regularly and had been wondering if I would be better to change up earlier, with the added benefit of saving stress on the engine? I do occasionally hit the limiter when trying to overtake. I certainly never take any track day corner (except the hairpin at Cadwell Park) in second, preferring to stay in third and use the grunt to pull me out of the corner. This has the added advantage of avoiding disappearing off stage left followed by a recovery truck, as the gap between 3rd and 2nd gears is quite large, and misjudging the revs when banging the clutch in in second can have noisy and alarming results!! On the plus side, one amusing effect of using second at the Cadwell hairpin is that if I forget to change up to third before Barn Corner, I get the most almighty explosion and flash of flame out of the exhaust as i back off the revs going into the corner - singes the eyebrows of anyone impertinent enough to be following me.
At Curborough sprints I stay at 6000 rpm in second around the twisties, as changing up to third just means changing almost straight back down again. It's annoying, as the track just doesn't suit the Chim's gearing. I only use third on the finishing straight. So hopefully I am using the power effectively. I must ask Peter what gears he uses, as he is consistently a couple of seconds faster than me. b
d!
In my Chim 400 days I would have had no doubt - power every time. I only asked the question because now I have a very torquey 500 and it feels more capable at lower revs.
I do in fact rev it to around 6000 rpm on track days regularly and had been wondering if I would be better to change up earlier, with the added benefit of saving stress on the engine? I do occasionally hit the limiter when trying to overtake. I certainly never take any track day corner (except the hairpin at Cadwell Park) in second, preferring to stay in third and use the grunt to pull me out of the corner. This has the added advantage of avoiding disappearing off stage left followed by a recovery truck, as the gap between 3rd and 2nd gears is quite large, and misjudging the revs when banging the clutch in in second can have noisy and alarming results!! On the plus side, one amusing effect of using second at the Cadwell hairpin is that if I forget to change up to third before Barn Corner, I get the most almighty explosion and flash of flame out of the exhaust as i back off the revs going into the corner - singes the eyebrows of anyone impertinent enough to be following me.
At Curborough sprints I stay at 6000 rpm in second around the twisties, as changing up to third just means changing almost straight back down again. It's annoying, as the track just doesn't suit the Chim's gearing. I only use third on the finishing straight. So hopefully I am using the power effectively. I must ask Peter what gears he uses, as he is consistently a couple of seconds faster than me. b
d!2nd all round then 3rd and fourth down the straight.
I gave a ride to a Z4 owner, gave it max beans with car snaking under braking, much tail wagging, smoking from rear and generally sawing at the wheel to keep it on line.
We did a 1.27, he was silent during the drive and his only comment after was, " that's the closest I've been to a near death experience"...........
I gave a ride to a Z4 owner, gave it max beans with car snaking under braking, much tail wagging, smoking from rear and generally sawing at the wheel to keep it on line.
We did a 1.27, he was silent during the drive and his only comment after was, " that's the closest I've been to a near death experience"...........
phazed said:
2nd all round then 3rd and fourth down the straight.
I gave a ride to a Z4 owner, gave it max beans with car snaking under braking, much tail wagging, smoking from rear and generally sawing at the wheel to keep it on line.
We did a 1.27, he was silent during the drive and his only comment after was, " that's the closest I've been to a near death experience"...........
Same as me then - and I guess you find yourself close to the limiter most of the time. I gave a ride to a Z4 owner, gave it max beans with car snaking under braking, much tail wagging, smoking from rear and generally sawing at the wheel to keep it on line.
We did a 1.27, he was silent during the drive and his only comment after was, " that's the closest I've been to a near death experience"...........
Is that the guy with the silver supercharged Z4M? The 520 bhp one that simply cannot get the power down? He's on Federal 595s, so it's not a lack of tyre grip. Wish I had been there now, instead of stuck in an office in Chelmsford with two women who won't turn the aircon on. I'd love to have seen how much better your car is now since finding the extra herd of horses.
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