I'm just wondering here...

I know going to redline is not the most effective way to go fast. You want shift to second so that the gear starts where the torque is. Anyway, for my car, that shift point seems to be between 5,000 and 5,500 rpm. I always shift there when driving fast, and it seems to work better then going to redline. Is it just a coincidence that this is where the hp and torque curves meet on MINIs? Or, is that like a magic spot of sorts for all engines?

 

your car may have a dip in there like min does even though my car hits 162whp it peaks at 6k then drops 25hp and climbs back up till redline where it peaks at about 162whp again , so usually when i shift at 6k it "feels" faster

 

hp = torque * RPM / 5252
So..... (theoretically) at 5252 rpm, hp = torque.
Not a coincidence, physics.
Not-too-technical explanation @ http://www.revsearch.com/dynamometer...orsepower.html
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Actually, with an engine like the MINI's where the torque doesn't fall off drastically at high RPM, you're better off shifting at redline for maximum acceleration.

The reason is, upshifting at any RPM on the MINI engine results in less torque to the wheels in the higher gear than you had in the lower gear, because you lose some torque multiplication in the transmission by shifting to the higher gear.

This thread has a good discussion on the topic. Be sure to check out the graph in post #22. It displays the *wheel* torque versus rpm for all six gears, and shows that upshifting will always cost you torque at the wheels compared to just staying in the lower gear as long as you possibly can. (Of course, if you have a different engine with an engine torque curve that drops like a stone at high RPM, or different transmission gear ratios, this doesn't always hold true.)

 

/\/\ yeah, what he said. Basically you want to avoid a situation where torque curve falls down drastically. I don't know what MINI torque curve looks like but if it's fairly flat and higher towards redline than it is at let's say 4000, than you're better off staying 'till redline.
You accelerate with torque, not with horsepower.

 

I don't see HP and tork meeting anyway on here. I forget who I stole this from but thanks, I still laugh my *** off at it.

 

ROFL! Great chart!

I tried increasing my torks with a tork wrench, but all it did was snap a bunch of bolts! Was I doing it wrong?

K, I'll now return you to your regularly scheduled thread...

 

I think that if you compare the spins vs the torks, there is a meeting (with powerpoint presentation) just before "|" and "_". It is a short meeting, and no refreshments will be provided. Please turn off your cell phones.
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You accelerate with torque, what total bull that is tell that to the N/A honda guys. 130# of tq and what 250 hp. will spank the crap out of all of us.
whateverman.....

 

I don't think so
you sound really knowledgeable about all of this
go read engine basics and how they work. You can make 1000hp but if you're not making torque you won't go anywhere.
Why do you think diesel engines feel "faster" and respond better to the throttle input during driving?
Simple google search yealded some interesting comparison between 2 BMW engines:
http://www.businessweek.com/bwdaily/...323_587549.htm

this of course is not limited to diesel. Take 2 cars with identical engines and identical HP numbers. Have one of them modified to have more of torque but still same HP and you'll see which one is faster

 

HP = T * N / 5252

Where T is in ft-lbs and N is in RPM.

so 130 ft/lbs at 10,000 rpm can be geared down to produce significant axle torque (say for example, 45 mph)

my mini makes 160 ft/lbs at 4,400 rpm, which in 2nd also equates to 45 mph

think of the gearing (imagine a DSP integra at the top of 1st gear! i've recently seen one of those...) between the two cars

the honda is reducing crankshaft to axle about two times compared to my car (10k rpm versus less than 5k) assuming we're running the same diameter wheel/tire combo (they are close)

so my car would have to make 260 ft/lbs at the crank to produce equal horsepower at only 4,400 rpm

that means the Integra in 1st at 45 should be kicking my butt

it is!



ps: you might say i'm cheating in this example, so let's consider that

what if i go apples to apples and put my mini in 1st?

it pulls 45 mph in first, but at almost 6,850 rpm, and at that speed the engine torque has fallen to only 125 ft/lbs - so the integra wins again! (not to mention that in the real world the integra would likely be at only 6k rpm with 2k left available - i'm on the limiter!)

 

hp is a product of torque. so you will have both, the question is where will you have it.

and also if hp and torque meet at 5252, then that is not necessarily the best place to shift, because they both drop off below that, may be better to shift approx 1000rpm above that so that the rpm drop puts the revs close to 5252 upon reopening the throttle.

correct me if i am wrong.

i also don't think that the integra is gonna beat a mini all the time, mini still has a good bit of plus on the integra. if they are both stock.

and what stock vehicle is revving to 10k? (nissan) sr20 guys are gunning for 9k at the limit with very built internals.

 

probably a bad example, but a there's a D Street Prepared integra running up here in New England Region that's a proper effort. I watched it run with two fast drivers at NHMS on a tight course, and it was in 1st and 2nd. Nowhere near stock of course!

 

Honda I believe is shooting for the first factory built vehicle to feature a 10K RPM redline. Or was it Acura in the new NSX...

 

If it's Acura then it's Honda...

 

A lot of good answers already.

The car pulls the hardest (produces the most Gs pushing you into the seat) @ the torque peak, which is what you are feeling and makes you think you are running "fastest" when shifting by 5K-5.5K; the pull is actually more at lower RPMs. So that is true, in any one gear.

However when you add torque multiplication from gearing into the equation, and how that reduces every time you upshift, when looked at in relation to the vehicle speed... The reality is when accelerating through the gears, you maximizes power, i.e. rotational torque to the wheels to produce work, when keeping the RPMs as near to the power peak as you can through the gears.

...and (assuming here) everyone thought theyd never need to use the calculus taught in school... i.e. This is all defined by using "Integration" to calculate the area under a curve... the power curve. The rule is you want to maximize the sum of the calculated areas under the power curve of each gear RPM range that is utilized, while upshifting through the gears. If you shift too soon in one gear [say, 5K], that takes too much away from the "area under the curve" calculated of the effective power being put to the tire's contact patch in the next higher gear. That maxes by keeping the RPMs as close to the power curve peak as you can; i.e. by upshifting just after the peak of the power curve to average your utilization through the power peak while running through the RPM range in each gear. Math rocks!

 

Good to know. I forgot how to do calculus, but I remember the basic ideas behind it.

 

Good post, except maximizing the area under the "engine power versus time" curve doesn't guarantee the maximum vehicle acceleration, because of the torque multiplication effects from the transmission that you mentioned.

What you want to do is maximize the area under the *wheel torque* versus time curve. Vehicle acceleration is directly proportional to wheel torque, and the proportionality constant (1/inertia) is a constant, so you can take it outside the integral. Thus, integrating wheel torque over time gives you a number that's directly proportional to vehicle speed.

Alternatively, if you want to integrate the power over time, you could do that too, but again, you'd need to use *wheel* power, not engine power, since the transmission de-multiplies power at the same time it multiplies torque.

With the MINI, the engine torque gained by upshifting in order to lower the engine rpm doesn't make up for the wheel torque lost due to reduced transmission multiplication in the higher gear, so you're better off just holding it in gear until redline.

It would be different with a car whose engine torque curve fell off faster above the torque peak, or if the transmission ratios were different, but in our case, upshifting from one gear to another at *any* rpm leaves you with less wheel torque (and therefore, less instantaneous acceleration) in the higher gear than you had in the lower gear.

 

Try this. Shift at a slightly higher rpm than what you mentioned. About 5500 to 5800 rpm. What happens is rpm will drop when you shift that will put HP a bit lower but then it will climb back up as rpm climbs since torque is still fairly strong up to about 5800 rpm. At 6000 rpm and higher torque tends to drop off a little more strongly.

If you shift at 5000 rpm then when rpm drops you get a much lower part of the HP curve so you have to climb back up through 6000 rpm which takes a bit of time.

Depending on your ECU tuning, your sweet spot might be a little lower like 5200 to 5400 rpm. I have RMW tuning and my best shift point is 5800 rpm.

You could try a couple of 0-60 runs and choose different shift point rpms and see how you do each time. I bet it would be easy to figure out what would give the best results.

 

I'll give you that. ... that's what I meant when I said "effective power being put to the tire's contact patch". The power curve is just a simple algebraic derivation from the torque curve using RPM. It undergoes multiplication in linear fashion as the torque curve through the transmission and differential, minus some linear and geometric parasitic losses.

I am not following what you mean in "transmission de-multiplies power at the same time it multiplies torque". I do not know "de-multiply" to be a word, and I'm not sure what you mean by it in your particular vernacular. I do however think we both mean the same thing in the end. One should operate in the RPM range to maximize the effective wheel power, not torque, thru the gears to maximize say 1/4 mile ET or 0-60, 0-whatever times. I too do understand that to be redline on the Mini.

I recommend CarTest2000 to eveyone that likes to fiddle with this stuff. Great simulation program, that can take your measure Dyno values @ the wheel and will optimize gearing or rear diff ratio for time to distance or time to speed ranges. ...just for kicks.

 

Yep - I think we're saying pretty much the same thing, although I still think it's more proper to talk about maximizing wheel torque over time, rather than power, given that torque is more closely-related to acceleration, and it's the time integral of acceleration that gives you velocity.

The time integral of power gives you total work done, which I admit you can translate into a velocity by equating the total work done to the change in kinetic energy, but in my mind, that just seems like the "long way around", compared to just maximizing torque (and therefore acceleration and final velocity) for the time period of interest.

 

5250 RPM is an ARBITRARY selected number for calculating HP and TQ figures, don't see how shifting at that point would make any difference. It was a number picked for making mathematical calculations only.

In GO FAST, you shift when the motor stops pulling, that is generally when the HP levels out at maximum and the TQ is actually starting to drop. Usually happens pretty close to redline on high rev motors.

 

I was just trying to explain the justification that it is the integral of the power curve, not the torque curve, that can and should be used to calculate what the optimal shift point should be, as the torque curve does not represent the force applied and in motion, which is what is needed to get a mass to either a distance or a speed over a set time, when more than one gear is being utilized. As you're saying that the integral of the power curve gives you total work done, it should be recognized that it is the work that was done -- through the gears, taking into account you only use the full RPM range in 1st and far less from 2nd on -- that results in a time to distance or time to speed of a mass, not instantaneous force that can be applied, which is what the torque curve gives.

I guess I'm just not understanding what you're meaning by "compared to just maximizing torque (and therefore acceleration and final velocity) for the time period of interest" if not looking at it in the power context. To me, shifting to maximize torque through each gear would have you shifting before 5K RPM ... As the gear you upshift to will be travelling through the RPM range where torque is maximum (gearing multiplication does not change the torque curve, just the adjusted value). That will result in probably 1sec longer to 60mph if not more, and many seconds longer in the 1/4 mile if one were to do that.

I know you're not saying that as you said one should be shifting @ redline. .. but the torque at and before redline in that engine just like any is much less at redline than at 6K, or 5.5K or 5K, etc... So it's when I read that from you that I'm getting confused about what you mean.

 

I thought I'd just throw out ... it's not completely arbitrary as in "pulled out of the hat". It is a derivation based on the combination, reduction actually, of several units of measure. Yes, "unit of measure" of any one "unit" is essentially arbitrary. But once we apply unit of measure, it become the frame in which we can determine and relate metrics.

 

Granted, this would be a *lot* easier to talk about in person, but I'm not saying that you should shift at the engine's torque peak.

Just plot out a graph of the *wheel* torque versus engine rpm for each gear. Then, for whatever gear/engine rpm you're currently at, ask yourself "will I have more torque at the wheels if I upshift now, or if I stay in the same gear?" Granted, if you stay in the same gear, the *engine* torque will continue to decrease if you're already past the engine's torque peak, but upshifting might cost you even *more* torque because of the loss of transmission multiplication.

I'd rather have 150 lbf-ft of engine torque at 6800 rpm, being multiplied 5:1 by the transmission in 2nd gear, than 175 lbf-ft of engine torque at 5500 rpm, only being multiplied 3:1 by the transmission in 3rd gear. Even though 6800 rpm is well past the engine's torque peak, the greater torque multiplication in the lower gear more than makes up for it.

By asking yourself this question at every instant on the wheel torque curve as you accelerate, you'll maximize wheel torque (and therefore acceleration) over time, and minimize your time to any particular final speed/distance.