Looking at the TTE turbo plot below - How does this translate into the best point in the rev range to shift gears when accelerating s:?: :?: s:?:
(http://i28.photobucket.com/albums/c229/fullSP/Powergraph.jpg)
look for the highest point in the toque curve and short shift
Quote from: "kanujunkie"look for the highest point in the toque curve and short shift
boy thats low down the rev range - need to get my gear changing arm in shape (its gonna need to be used quickly) - luckily its the same arm as i drink with so well developed already s:D :D s:D
Quote from: "ninjinski"luckily its the same arm as i drink with so well developed already s:D :D s:D
s:lol: :lol: s:lol: s:lol: :lol: s:lol: s:lol: :lol: s:lol: s:lol: :lol: s:lol:
Just try and change before you hit the rev limiter s:twisted: :twisted: s:twisted:
Quote from: "TommyD"Just try and change before you hit the rev limiter s:twisted: :twisted: s:twisted:
OK, I am sure there are plenty of posts about it, elsewhere if not here, but can somebody explain to me the relationship between torque and power (bhp).
On the above graph max torque is 3,500 - 4,500, but max power is at 6,500. Do you change at 4,500 or 6,500?
Sorry, i missed that lesson in Physics - and failed the A-level !
Gotta say that if I had a turbo, woulld be revving it out way beyond the highest point in the torque curve - limiter here I come!
A quick google found a spread sheet that you can use to calculate it (admitedly for a bike but can't be that much different):
m http://www.timberwoof.com/motorcycle/shiftpoints.html (http://www.timberwoof.com/motorcycle/shiftpoints.html) m
I don't know much but wouldn't you want to maximise the power and not the torque?
just remember one thing, torque=available power to the gearbox, BHP=cock all without any torque. I'm no good at explaining physics i'm afraid Roger
here (http://www.carkeys.co.uk/features/technical/636.asp) is good.
Power is what a car needs to accelerate. Power= revsxtorque over a constant (5252) You would also want to be changing high enough up so you hit the peak torque for the next gear. s8) 8) s8)
Quote from: "kanujunkie"just remember one thing, torque=available power to the gearbox, BHP=cock all without any torque. I'm no good at explaining physics i'm afraid Roger
Depends on gearing. If a car has twice the rpm but half the torque, it can put out similar power to a car with half the rpm but the full amount of torque s:? :? s:?
Quote from: "Bongo"A quick google found a spread sheet that you can use to calculate it (admitedly for a bike but can't be that much different):
m http://www.timberwoof.com/motorcycle/shiftpoints.html (http://www.timberwoof.com/motorcycle/shiftpoints.html) m
I don't know much but wouldn't you want to maximise the power and not the torque?
Threw a few figures in....it suggested I should change from 1st - 2nd at 170mph!!
Told you physics wasn't my strong point
On a turbo'd '2, you'll be lucky to try and differentiate between shifting at 5K or 7K rpm in first and 2nd gear, as the needle swings round pretty quickly!
If I'm giving it some beans, I still shift at the same point as I did when I was N/A, which is at about 6.5K (or as near as I can get it bearing in mind my comment above).
I've yet to try a full-on launch whilst holding 3-4K revs, as it's too wet and cold and I just sit there wheel spinning at WOT. s8) 8) s8)
Surely the best time to change depends on where the revs land, once you're in the next gear. It's stupid changing at 3500RPM in 3rd when you drop down to 2000 – 2500rpm in 4th
so you really need to know the gear ratios.
Quote from: "Roo"here (http://www.carkeys.co.uk/features/technical/636.asp) is good.
Power is what a car needs to accelerate. Power= revsxtorque over a constant (5252) You would also want to be changing high enough up so you hit the peak torque for the next gear. s8) 8) s8)
Very good article!!
Quote from: "Roo"here (http://www.carkeys.co.uk/features/technical/636.asp) is good.
Power is what a car needs to accelerate. Power= revsxtorque over a constant (5252) You would also want to be changing high enough up so you hit the peak torque for the next gear. s8) 8) s8)
Thanks Roo, very interesting. I can see now why people want an S2K. Also interesting to see an F1 car only produces about 260 lb/ft !
Quote from: "Ekona"On a turbo'd '2, you'll be lucky to try and differentiate between shifting at 5K or 7K rpm in first and 2nd gear, as the needle swings round pretty quickly!
If I'm giving it some beans, I still shift at the same point as I did when I was N/A, which is at about 6.5K (or as near as I can get it bearing in mind my comment above).
I've yet to try a full-on launch whilst holding 3-4K revs, as it's too wet and cold and I just sit there wheel spinning at WOT. s8) 8) s8)
Mate how much quicker do u change gear now when pushing on hard? Silly question really but just trying to get an idea! ta
Quote from: "roger"Quote from: "Roo"here (http://www.carkeys.co.uk/features/technical/636.asp) is good.
Power is what a car needs to accelerate. Power= revsxtorque over a constant (5252) You would also want to be changing high enough up so you hit the peak torque for the next gear. s8) 8) s8)
Thanks Roo, very interesting. I can see now why people want an S2K. Also interesting to see an F1 car only produces about 260 BHP !
260 torques
"If 800bhp is produced at, say, 16,000rpm (and some Grand Prix cars can go far higher), that equates to a torque figure of only 262.6lb/ft"
Caught me! As soon as I read it I realised I got the wrong unit s:cry: :cry: s:cry:
Thats the thing with an S2K.
My old car, a Seat Ibiza Tdi Sport had loads of torque (330nm) at 2200 rpm, but only revved to 4000rpm so it felt like it was accelerating really quickly and you'd get a massive shove in the back. Put it against a petrol with half the peak torque and double the revs and see what happens! The optimum point has to be somewhere after the peak torque and before the peak BHP, where the torque tails off too much for the revs to multiply it more effectively than revving lower at a higher ratio - i.e. lower gear. The more torque at higher revs, the better = why an S2k has a good strong engine.
Gearing is v. important as is weight. As I said above chaging at peak torque would drop you below peak torque in the next gear. You are better to rev higher and multiply the torque by RPM for a fair bit before the laws of diminishing returns cause you to change up. I should think this would be quite near redline in our cars.
Cheers
Roo s8) 8) s8)
Quote from: "edward.carter"Quote from: "roger"Quote from: "Roo"here (http://www.carkeys.co.uk/features/technical/636.asp) is good.
Power is what a car needs to accelerate. Power= revsxtorque over a constant (5252) You would also want to be changing high enough up so you hit the peak torque for the next gear. s8) 8) s8)
Thanks Roo, very interesting. I can see now why people want an S2K. Also interesting to see an F1 car only produces about 260 BHP !
260 torques
"If 800bhp is produced at, say, 16,000rpm (and some Grand Prix cars can go far higher), that equates to a torque figure of only 262.6lb/ft"
262 lb/ft - my Ibiza produced 230 lb/ft - could it at peak rpm out drag an F1 car..lol or would the F1 car have more power available through revving longer through longer gearing...lol lowerish torque over a higher rpm spread is better than higher torque for a very short rpm, multiplier effect.
Quote from: "ninjinski"Mate how much quicker do u change gear now when pushing on hard? Silly question really but just trying to get an idea! ta
A hell of a lot quicker is the answer. When I say that the revs just fly by, I'm not exaggerating at all (ask one of the other turbo guys, they'll confirm this I'm sure), and you really do have to take notice of what the rev needle is doing. It's a lot harder to shift by ear in 1st and 2nd, as the revs fly too quickly and you need to concentrate on holding the wheel steady. That's not to say it's an out of control fly by the seat of your pants thing, more that I tend to keep one eye on the rev counter and one on the road when giving it some.
You're technique will be the most important thing. Smooth and quick is the best way to go - I know that's the best way full stop, but it's more important on a turbo '2 than N/A. IMHO, obviously. s:wink: :wink: s:wink:
Quote from: "kanujunkie"just remember one thing, torque=available power to the gearbox, BHP=cock all without any torque.
but who is saying any other kit is low torque ? higher power and same torque would be better still. I mean.
Quote from: "Ekona"Quote from: "ninjinski"Mate how much quicker do u change gear now when pushing on hard? Silly question really but just trying to get an idea! ta
................It's a lot harder to shift by ear in 1st and 2nd, as the revs fly too quickly and you need to concentrate on holding the wheel steady. ........
Actually that reminds me someone did mention that the xtra power could cause front wheel unstability when accelerating s:!: :!: s:!: Comments s:?: :?: s:?:
I've not noticed any major instability: It's no different than N/A, you just tend to hand on a bit more as you're going a hell of a lot faster much quicker! s:D :D s:D
Quote from: "Roo"Quote from: "kanujunkie"just remember one thing, torque=available power to the gearbox, BHP=cock all without any torque. I'm no good at explaining physics i'm afraid Roger
Depends on gearing. If a car has twice the rpm but half the torque, it can put out similar power to a car with half the rpm but the full amount of torque s:? :? s:?
that was why i said torque available to the gearbox
with you now stu! I was thinking low torque over many thousand rpm can = higher power than high torque over a few rpm therefore power doesnt equal cack all if you have the rpm to produce it.. which in turn brings us back to gearing..lol
Im dizzy
I don't know if any of the posted links contain the answer to the original question, but here it is from a mechanical engineer.
assuming you will be shifting more than one gear:
1: find the difference in rpm of the engine at a set speed between the gear you are in and the next. we will call this x rpm
2: find the starting rpm and finishing rpm separated by x rpm which has the greatest area under the HP curve. the upper of these points is the rpm of your shift. the lower is the rpm you will be at in the next higher gear.
3: repeat step two until you are in the highest gear you will be accelerating in.
4: for your last upshift, shift at Y rpm, where the hp avalable at Y rpm first becomes less than the HP at Y minus X rpm, or, if that does not occur before redline, shift at redline.
I can think of only one situation where following these rules would not result in the best possible (max acceleration) shift points, and that is on an uphill in a situation where the last shift comes so close to the end of acceleration that the time wasted coasting in the shift would be better spent bouncing the rev limiter
Richard
Quote from: "Rocwandrer"1: find the difference in rpm of the engine at a set speed between the gear you are in and the next. we will call this x rpm
2: find the starting rpm and finishing rpm separated by x rpm which has the greatest area under the HP curve. the upper of these points is the rpm of your shift. the lower is the rpm you will be at in the next higher gear.
That's a good rule of thumb, but not the full truth.
Say the above ends you up with a range, where your area starts and ends with 100hp. Now would it be best to change from 2nd at 100hp to 3rd with 100hp, or from 2nd at 99hp to 3rd with 101hp? The gearing does make a difference and you get better acceleration with less hp with higher gearing.
Quote from: "Tem"Quote from: "Rocwandrer"1: find the difference in rpm of the engine at a set speed between the gear you are in and the next. we will call this x rpm
2: find the starting rpm and finishing rpm separated by x rpm which has the greatest area under the HP curve. the upper of these points is the rpm of your shift. the lower is the rpm you will be at in the next higher gear.
That's a good rule of thumb, but not the full truth.
Say the above ends you up with a range, where your area starts and ends with 100hp. Now would it be best to change from 2nd at 100hp to 3rd with 100hp, or from 2nd at 99hp to 3rd with 101hp? The gearing does make a difference and you get better acceleration with less hp with higher gearing.
No, it sounds like you are talking height, not area under the curve...
Having maximum area under the curve between the two points mentioned rarely results in the same HP after the shift as before. There are smart, knowledgeable people who will tell you torque is a better indicater of power at low rpm, or something similar. In simple (slightly inaccurate) terms, acceleration is about energy, hp is a measure of energy, and the maximum average energy over the period of time (actually rpm range covered...) in a gear results in the maximum average acceleration, which is what anyone asking this question wants.
Quote from: "Rocwandrer"No, it sounds like you are talking height, not area under the curve...
That's basically the same thing in my example, because the gearing won't change and you have to cover the same rev range. s;) ;) s;)
Just think about it. Choose any power/rpm point on your car. Then floor the pedal on that point. Do it with 2nd and 3rd gear, which is faster?
The area under the curve is the right answer to getting from x rpm to y rpm, but it doesn't consider gear changes. I'll try to explain it again. Say your maximum area under the curve is a symmetrical triangle, starting with 100hp at 4000rpm, going to 150hp at 5000rpm and down to 100hp at 6000rpm. That's your fastest way from 4k to 6k in one gear.
But in real life you usually have to change gears. So you do it from 100hp at 6000rpm on 2nd to 100hp at 4000rpm on 3rd. You'll notice it won't accelerate as fast on 3rd as it just did on 2nd, even though you have the same power. Now consider which is faster, 99hp on 2nd or 101hp on 3rd. Maybe it would be best to stretch beyond the maximum area under the curve on smaller gear? Just so you can get more power on the lazier bigger gear.
(...yes, if you really want to calculate it, you'll need to know the gearing, mass, wind resistance and alikes. I'm just saying it's not that simple...)
Quote from: "Tem"But in real life you usually have to change gears. So you do it from 100hp at 6000rpm on 2nd to 100hp at 4000rpm on 3rd. You'll notice it won't accelerate as fast on 3rd as it just did on 2nd, even though you have the same power. Now consider which is faster, 99hp on 2nd or 101hp on 3rd. Maybe it would be best to stretch beyond the maximum area under the curve on smaller gear? Just so you can get more power on the lazier bigger gear.
Which is why it's worth accelerating past peak torque towards peak BHP until diminishing returns mean that a greater level of acceleration is achievable from a higher gear, and therefore change up.
Quote from: "Tem""stuff"
hey, I am not trying to convince you, I just dislike the idea that someone might search for the answer to this question, and see wrong answers which no one contested... I am sure from your view point, you were doing the same thing.
I'm done :-) :-) :-)
Quote from: "Rocwandrer"someone might search
Like that would ever happen s:lol: :lol: s:lol:
Quote from: "Tem"Quote from: "Rocwandrer"someone might search
Like that would ever happen s:lol: :lol: s:lol:
s:lol: :lol: s:lol: s:lol: :lol: s:lol: s8) 8) s8)