You accurately log your best acceleration times in only one gear on a manual box. Say in 5 mph increments - if you could do such a thing.
Like say 20-25, 45-50 mph, etc.
Where would be best figure be - maximum torque, maximum BHP, or somewhere else?
Perfect surface and no wheel spin. And at the sort of speeds where air drag doesn't make a difference.
Peak acceleation.
Moderator: phpBB2 - Administrators
I would have thought that it would be at maximum torque, the gearbox acts as a torque 'multiplier' but initially the torque is being produced at the crankshaft.
Max BHP is related to torque but also to the actual revs per minute of the crank and this in turn relates to the MPH. That's why your maximum speed is determined by your max BHP. Once your engine has revved higher than where it produces peak torque your acceleration will start to drop off but it will still continue to accelerate as you are still producing torque. When the torque starts to drop at such a high rate that the increase in RPM is not great enough to result in an increase in BHP you have then hit your peak BHP.
Max BHP is related to torque but also to the actual revs per minute of the crank and this in turn relates to the MPH. That's why your maximum speed is determined by your max BHP. Once your engine has revved higher than where it produces peak torque your acceleration will start to drop off but it will still continue to accelerate as you are still producing torque. When the torque starts to drop at such a high rate that the increase in RPM is not great enough to result in an increase in BHP you have then hit your peak BHP.
Well whoever told you that does not have a clue about what torque or BHP is!DaveEFI wrote:Just what I'd always thought. But just been told in no uncertain terms it would be at maximum BHP, not torque.
I tend to spend hours and hours in the bath reading books on all this sort of stuff. A.G. Bells book on 4 strokes has a good section on gearing and gearboxes, my first post was based on the info from that book!
(All of my books are wrinkly!)
You sort of even know this subconsciously anyway, you tend not to rev the engine to peak RPM (peak BHP) in first gear beacuse you have gone way past peak torque, you do rev the engine above peak torque in each gear because when you change up you need the engine revs to drop back onto the fat bit of the torque curve. The gear change point for maximum acceleration changes for each gear that you are in but I must admit that I tend to just rev the engine hard in every gear other than first! Ofcourse the wheels just to tend to spin up anyway! (A racer after every 1/10 of a second would be more interested in this stuff than me I guess)
Last edited by sidecar on Thu Mar 31, 2016 9:05 pm, edited 2 times in total.
And at the sort of speeds where air drag doesn't make a difference.
Thats on a Dyno I guess !! Peak torque rpm is the key here i think ?
Thats on a Dyno I guess !! Peak torque rpm is the key here i think ?
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
Max BHP
You want to accelerate something and that's all about moving and Power is an ability to move and do work.
Torque is about an ability to twist/turn something and requires no movement - I can generate more torque than my V8 (at zero rpm) but to do it at 7000rpm - Nah - that's power.
You want to accelerate something and that's all about moving and Power is an ability to move and do work.
Torque is about an ability to twist/turn something and requires no movement - I can generate more torque than my V8 (at zero rpm) but to do it at 7000rpm - Nah - that's power.
4.5L V8 Ginetta G27
I just googled this, now I'm not saying that just because the first site I came across says its peak torque therefore I'm right. I reckon its peak torque anyway!Darkspeed wrote:Max BHP
You want to accelerate something and that's all about moving and Power is an ability to move and do work.
Torque is about an ability to twist/turn something and requires no movement - I can generate more torque than my V8 (at zero rpm) but to do it at 7000rpm - Nah - that's power.
The conclusion from the website...
But, you ask, isn't your acceleration greatest at the torque peak? Yes, it is! But only within that gear. The next gear down will give you even greater acceleration at the same speed, unless the vehicle speed is too high for that gear
The website...
http://www.allpar.com/eek/hp-vs-torque.html
Mind you it also says this....
Shift to maximize engine POWER, not engine torque!
But I think that is with regards to changing gear and as the OP said implied for a single gear I think that in that gear no matter what that gear is the peak rate of acceleration will be at peak torque.
Last edited by sidecar on Fri Apr 01, 2016 2:34 pm, edited 1 time in total.
My car goes quickest when I shift gears at peak torque rpm. If I shift at peak bhp rpm it goes slower on the 1/4 mile.sidecar wrote:Well whoever told you that does not have a clue about what torque or BHP is!DaveEFI wrote:Just what I'd always thought. But just been told in no uncertain terms it would be at maximum BHP, not torque.
I tend to spend hours and hours in the bath reading books on all this sort of stuff. A.G. Bells book on 4 strokes has a good section on gearing and gearboxes, my first post was based on the info from that book!
(All of my books are wrinkly!)
You sort of even know this subconsciously anyway, you tend not to rev the engine to peak RPM (peak BHP) in first gear beacuse you have gone way past peak torque, you do rev the engine above peak torque in each gear because when you change up you need the engine revs to drop back onto the fat bit of the torque curve. The gear change point for maximum acceleration changes for each gear that you are in but I must admit that I tend to just rev the engine hard in every gear other than first! Ofcourse the wheels just to tend to spin up anyway! (A racer after every 1/10 of a second would be more interested in this stuff than me I guess)
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
We can all waffle on about it but if you have tested it down the strip and the tests are repeatable then I guess that's more conclusive than any theories or quoting of books!mgbv8 wrote:
My car goes quickest when I shift gears at peak torque rpm. If I shift at peak bhp rpm it goes slower on the 1/4 mile.
sidecar wrote:I just googled this, now I'm not saying that just because the first site I came across says its peak torque therefore I'm right. I reckon its peak torque anyway!Darkspeed wrote:Max BHP
You want to accelerate something and that's all about moving and Power is an ability to move and do work.
Torque is about an ability to twist/turn something and requires no movement - I can generate more torque than my V8 (at zero rpm) but to do it at 7000rpm - Nah - that's power.
The conclusion from the website...
But, you ask, isn't your acceleration greatest at the torque peak? Yes, it is! But only within that gear. The next gear down will give you even greater acceleration at the same speed, unless the vehicle speed is too high for that gear
The website...
http://www.allpar.com/eek/hp-vs-torque.html
The summary from that website
Torque and power are (almost) flip sides of the same coin. Increasing the torque of an engine at a particular RPM is the same as increasing the power output at the same RPM.
Power is just as useful and relevant in determining vehicle performance as is torque. In some situations it's more useful, because you may not have to play with gear ratios and a calculator to understand what's going on.
A car accelerates hardest with gearing selected to stay as close as possible to the engine *power* peak, subject to the traction capability of the tires.
Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points.
end quote.
And the bold is what the OP asked ignoring any of the relevant things like traction and wind etc.
Max torque could be at 5 RPM - that's not quick and if you change the gearing you change the torque as its all 5250 connected.
This is to go fast and accelerate quickly you go for Power and turn the engine as fast as possible and use the gearing to maximise the torque at the wheels.
Question was pretty pointless TBH
If torque was king no engine would need to run at higher than 5250 rpm accelerate as fast as possible and we know that is not a fact.
4.5L V8 Ginetta G27
sidecar wrote:We can all waffle on about it but if you have tested it down the strip and the tests are repeatable then I guess that's more conclusive than any theories or quoting of books!mgbv8 wrote:
My car goes quickest when I shift gears at peak torque rpm. If I shift at peak bhp rpm it goes slower on the 1/4 mile.
Just the results of my own testing !!
I had a read up on the whole thing about this online and to be honest I glazed over after a few mins
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
sidecar wrote:We can all waffle on about it but if you have tested it down the strip and the tests are repeatable then I guess that's more conclusive than any theories or quoting of books!mgbv8 wrote:
My car goes quickest when I shift gears at peak torque rpm. If I shift at peak bhp rpm it goes slower on the 1/4 mile.
Just the results of my own testing !!
I had a read up on the whole thing about this online and to be honest I glazed over after a few mins
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
Unless you have a CVT covering all possible speeds, you will always have to run the engine outside its 'perfect' speed no matter what that is.Darkspeed wrote:
[snip]
If torque was king no engine would need to run at higher than 5250 rpm accelerate as fast as possible and we know that is not a fact.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
