question on torque and shifting

[matchuk]

i just been doing some reading and just want to clarify something, the powerband is the range of rpm with max torque right? what happens if max torque occurs before redline or max rpm, then in theory u would want to upshift alil above max torque but before redline... if thats case why do most people shift redline???

also anyone have an idea where a stock h22a prelude 94vtir powerband lies??

thanks in advance

[aaronng]

You should shift at peak power, not at peak torque. Because once you shift at peak torque, you end up further below peak torque RPM. If you shirt at peak power RPM, then you will probably end up closer to peak torque RPM and have better acceleration.

[SeverAMV]

ideally, it depends on the shape of your power band. but from a mathematical point of view, if your car doesnt lose too much power between peak power and the redline, then you should shift at the redline, as after the upshift, you will be at a higher power point than if you shift at the peak power point. essentially its the power under the curve, curve area is greater if the average power is greater.

[Limbo]

ideally, it depends on the shape of your power band. but from a mathematical point of view, if your car doesnt lose too much power between peak power and the redline, then you should shift at the redline, as after the upshift, you will be at a higher power point than if you shift at the peak power point. essentially its the power under the curve, curve area is greater if the average power is greater.


that logic sounds good to me, pretty much what i have done with all my cars

[JohnL]

i just been doing some reading and just want to clarify something, the powerband is the range of rpm with max torque right? what happens if max torque occurs before redline or max rpm, then in theory u would want to upshift alil above max torque but before redline... if thats case why do most people shift redline???

also anyone have an idea where a stock h22a prelude 94vtir powerband lies??

thanks in advance

Max torque always occurs well before the redline, as does max horsepower (though closer to the redline, more or less so depending on the engine). The only exception to this will be when an engine has been modified in such a way that the powerband is moved much higher in the rpm range, possibly so high that you don't rev the engine that hard for fear of blowing it up, or the valves start bouncing before power starts to fall off (this would be an unwisely set up engine).

You want to upshift when the engines reaches an rpm that will cause the rpm to be at (or very near to, but slighty below) max torque when the next higher gear is selected. This might mean revving the engine past the point at which max horsepower is being produced, but with correct ratios in the box you shoud be able to shift before the horsepower starts to drop off significantly.

With poor ratio choice (or an engine modified so the power band is too narrow, so power band doesn't match the gaps between gear ratios) you might have to rev the engine too far past peak hp and still be too far below peak torque in the next gear. In this case you need to revise the ratios or revise the engine tuning to increase the breadth of the power band (even if this means producing less peak power, which it probably will).

A lot of modded engines produce a heap of peaky power (i.e. over a narrow rpm range), but not much outside that power band. With such an engine you need a close ratio gearbox. If you don't want or can't fit a close ratio box then engine mods need to be reasonably conservative, there's little point in having a heap of power if your gear ratios don't suit it.

With a lot of stock engines there's little point in revving the engine to the redline because the power is dropping off a lot by the redline, and when you select the next gear you may find the rpm to be above max torque in the next higher gear (so you miss some part of the 'good' power band). In such a case it can be better to 'short shift' to some degree. This does depend on the gearing though, you still don't want to be too far below max torque when you select the next gear. With my CB7 the redine is 6300, but I never rev it this high as it's slower than shifting at 5500.

[AzKik-R]

i just been doing some reading and just want to clarify something, the powerband is the range of rpm with max torque right? what happens if max torque occurs before redline or max rpm, then in theory u would want to upshift alil above max torque but before redline... if thats case why do most people shift redline???

also anyone have an idea where a stock h22a prelude 94vtir powerband lies??

thanks in advance

2 main reasons
firstly, when it comes to acceleration, 1st gear has a better ratio then 2nd gear, 2nd gear has better acceleration then 3rd and so on and so on. This case is especially true with n/a engines. Staying in each gear as long as possible allows you to enjoy that gear ratio for as long as possible. The lower the gear the better the acceleration gear ratio

secondly, when you've changed gear, you want the power to be on tap pretty quickly, rather then waiting for the power to build up. Its important that when you've completed your gear shift, that the rpm lands in a good spot on the power charts. Shifting too Early may mean that your revs land on a low power zone, and shifting too late means, you're car is going to be bouncing off the rev-limiter.

another reason, not so major, shiting gears takes time. We try to keep time to a minimum.

These reasons in mind.

It will always be optimal shifting just before the redline.
Manufacturers use the redline shift for all their acceleration tests. By logic, they wouldn't post slow accelerations times (that and maybe because its consistant shifing at red)

[matchuk]

just a bit of theory here please correct my way of thinking

http://www.drhess.net/images/4a-ge_20_dyno.gif
using this torque dyno from and the gear ratios 3.166-->1.904

the greatest torque band would be starting from 4500 to about 7000 rpm right

meaning we want to be at 4500 rpm after dropping revs gettin into 2nd gear

hence X/3.166 x 1.904 = 4500 where X is optimal shift pt

hence we should shift at X = 7482 around 7500 rpm??

in the end power in kw or hp creates torque which really determines acceleration am i correct ???

[aaronng]

^^ Actually, torque x rpm x factor is what creates power.

[Bludger]

just a bit of theory here please correct my way of thinking

http://www.drhess.net/images/4a-ge_20_dyno.gif
using this torque dyno from and the gear ratios 3.166-->1.904

the greatest torque band would be starting from 4500 to about 7000 rpm right

meaning we want to be at 4500 rpm after dropping revs gettin into 2nd gear

hence X/3.166 x 1.904 = 4500 where X is optimal shift pt

hence we should shift at X = 7482 around 7500 rpm??

in the end power in kw or hp creates torque which really determines acceleration am i correct ???seriously, why are you bothering with all these figures???

are you doing some sort of project???

I would just use my 'bum-o-meter' to judge when its best to shift to get the most performance....

[matchuk]

nuh not doing a project just personal interest understanding certain things

[JohnL]

in the end power in kw or hp creates torque which really determines acceleration am i correct ???

No. Torque is a measure of force, and power (horsepower, kilowatts etc) is a measure of 'work' being done. This is interelated but quite distinctly different, and the source for endless confusion. 'Power' is another word for 'energy' which is a different 'thing' to force (i.e. force can exist when zero energy exists).

For an 'accelerating' vehicle, the more torque we have the better, but torque on it's own is useless, unless we're tightening a bolt or nut (though this is actually an example of a high torque / low power application rather than a zero power application). Keep in mind that force can exist when zero or little work is being performed, and zero work = zero motion. We need motion to exist in addition to torque in order to have something useful for a vehicle in motion.

I suppose it could be suggested that power = force X time, since motion must be involved and motion must take place over time. This is I think implicit in the concept of power being 'torque X rpm', where we should note the 'm' in rpm.

Some people seem to think of torque and power as being in some way independant from each other, i.e "torque is what you get at low rpm and power is what you get at high rpm". This is of course completely wrong.

A 'torquey' motor (i.e what is commonly thought of as 'torquey') with a good bottom end but poor top end has a lot of torque at low rpm, which equates to a lot of power at low rpm (i.e. a big number X a small number = X power). A 'power' engine with poor bottom end but good top end has poor torque at low rpm but good torque at high rpm, so power is poor at low rpm but good at high rpm (i.e. a big number X a big number = Y power).

Note that when we make best torque at high rpm that we can then make more power (which is what we're really after) because we are multiplying a big number with a big number, rather than when we make best torque at low rpm where we multiply a big number with a small number.

This is why very 'torquey' engines tend to have a large cubic capacity, because large capacity can more easily create very big low rpm torque and thus good power at low rpm (the sort of thing you want for big heavy sedans where 'lazy' / effortless acceleration at 'town' speeds is more important than frantic flat out performance at higher rpm).

Matchuk,
At this stage I think you need to postpone trying to make sense of particular torque / hp numbers for particular engines, and do some more basic research on the first principles of power and torque. If you type 'power vs torque' into a search engine I expect you'll be spoilt for reading material...