SharkSkin

I think that's what I was saying -- also in the last post of mine you quoted, I meant to say "If one car had different gears, for example max speed in 2nd was say 45, 3rd 65, etc"

mark kibort

Gotcha.

The different gears gets into the "gear ratio" discussion where there are trade offs as well, based on operational speed ranges.

I run against these same BMWs that do have different gears. often the BMW guys have either 3.73, or 4.10 gears. ive run agains both with near equal HP to my car. the differences are very subtle

Its all about HP/seconds. Whoever can apply the most HP/seconds, will win the race!

mk

GlenL

Actually you mean HP*seconds. That'd be energy.

Now torque*seconds is meaningless by itself, but F=ma so lets say m*a*t. Well, that'd be m*v or momentum. Not quite energy, but you get the point.

mark kibort

Oops, wrong key stroke. ment to say, Hp-seconds.

like, killowatt-hours. unit measure of work, not power.

yes, torque*seconds, is meaningless by iteself, just as engine torque is meaningless by itself. momentum is not energy as well, missing the 1/2 and the ^2.

so, who ever applies the most amont of hp over the greatest time, wins.
energy! Yes!

Mk

GlenL

OK, I'll forego the difference between work and energy. I mean, gotta keep some secrets from y'all.

Did I say "meaningless." How batting practice of me.

One thing your pointing out, though unintentionally, is why power is decpetive as speed increases. It's takes an additional 3 parts to get two times faster while torque computations are linear. F=ma; it's the law!

Oh well, gotta grab dinner. Then a classic Bond movie with shaken beverage. Chicka, chicka, chicka, chicka.

tommytomaso

Mark...its worse then you think....EVEN PORSCHE dosnt agree with you.....well not on some points, like the VALUE of torque. Christophorus No.301 April/May 2003 artical on the misconseptions of TQ and its relationship to HP....but then again they are only the PORSCHE engineers.
"" Of all the important factors that indicate the abilities of a car,torque is the one most often ignored. Unjustly so-for it ensures that output will be translated into driving power."" quote from opening artical. = )

tommytomaso

we should all take note that many engine builders like Inline 6s because they "pull like a V8" I remember my first drive in a Z3 with the I6 ..very much reminded me of my 72 340 cuda' (Z3 was a way nicer ride....could go stop and turn) im just surprised so little companys use the I6..whos left BMW,JAG Aston Martin and the Big Desiel Guys?

mark kibort

Well, this is ONLY true if you are talking about rear wheel torque. The engineers are talking specifically about torque by definition. yes, torque x rpm/5250 is HP. so yes, its a big part of HP. (1/2 and the other 1/2 is rpm)

So, yes the engineer maybe talking about usable torque or torque multiplied through the gear box. but make no mistake, and ill debate this with any engineer, engine torque is irrelavant with out discussion of RPM, as i have shown, UNLESS you tie an rpm to it. the net torque to the wheels multiplied through the gear box is DETERMINED by hp and the HP curve. Acceleration = power/(mass x velocity)

I trust Netwon, more than i trust a translation of a german engineer on a concept that MOST engineers have a hard time explaning (in my professional experience and opinion). "torque assures that the output is translating to driving power" Hmmmm. this is one of those non technical bastardizaitions of physics terms.
if im at max engine torque, do i have the max "driving power"???? Absolutely not. But, this is probably a techy marketing blirbs that snuck through proof reading!

If this where true, than why doesnt the bmw with 50ftlbs less engine torque, ever show any weakness against the mighty V8, at ANY speed?

The EPA also says that changing your air filter saves gas with FI engines! do you believe that?? another discussion! There are all sorts of errors with many things that are said by folks that know better!


Mk

mark kibort

and so does the Inline 4 when it has the same hp curve as well. its all about making an engine breath. more air, more fuel = more HP.

There is even confusion with the Audi engineers with the R10 vs the R8 (mega torque turbo diesel vs turbo gas racer) they said special tires would be needed, because of the massive torque. however with the same HP at any speed, the torque to the rear wheels will be the same. sure it had a very flat HP curve( notice i didnt say the often an mistakenly explaned, flat torque curve), but the usable hp range was 550hp vs the older R8 high reving turbo which also had 550hp.. the ONLY difference was that there was less shifttig with the diesel, and first stage gears had to handle 800+ ft-lbs of torque, while at the CV joints, the same torque was present with both. (and for the special tires) all marketing to hype up new gas and engine technology.

if you ever have doubts look at the BMW I6 vs porsche V8 dyno chart comparison. it explains a lot!

Mk

tommytomaso

Mark ...so ture about PR...you can prove all your points if you can find two SAME cars.. SAME HP
SAME ENGINE SIZE SAME WEIGHT SAME GEARS....but diferant TQ.....ops ...same tire weight and size........all your charts...to my eyes only show the ripples not the true depths why you think TQ is irrelivent.....spinning mass...weight ,Final gearing and im sure im missing about 10 other corosponding mutipliers and dividing factors... that make the whole story. = )

mark kibort

And you got to love power required goes up with the cube of speed!! (as you reminded us) came in handy when looking at the power required for driving my wing at the higher speeds, even though that was less than most folks thought. (50 more lbs of downforce, is 5lbs of drag, or 5ft-lbs of torque at the rear, through the gear box at 4.5:1 at 100mph, is 1.1ft-lbs on the engine or 1.16hp. Now, at 150mph, its 11.25lbs of drag, 11.25ft-lbs and 3.5ft-lbs to the engine through a 3.2:1 gear box so, 4hp! cubed!)

so, power x seconds is energy. you pay for it at the meter like this. (killowatt/hours) batteries are measured by it (amp-hours, at a given voltage)

but momentum is not. without knowing its components, its as usless in dermining energy as the term torque is. I can have big mass and little velocity, or little mass and big velocity. two different stored energy situations
The net force equals rate of change of mometum just as the rate of change of kenetic energy is power. so, as far as momentum is concerned, it doesnt care if you have a small force over a long period of time or a great force over a short period of time.

mk

mark kibort

You are going down the rat hole of confusion. yes, if it all is the same, then you can compare the two factors in question. Are we good with torque being irrelavant if the HP curves are identical shapes?

Now, what do you want to change? Im good with that too.

Next most common would be two cars with the same HP to weight ratio,and then proportional curves. ahh, but then you have to compare HP to drag ratios too. it gets better. one thing nice about the dyno is that incorporates much of what you just seemed to be tossing out there. gearing doesnt matter if they are creating the same MPH shift points, inertia of the tires, engine, etc, all show up with the rolling chassis dyno. we kept that the same for the understanding of the relatioinship of ONLY hp vs torque.

We are comparing two vehicles of the same weight and that have the same HP curve shapes.
In actuality, there would be other factors, but subtle at best. areo, gearing choices, (which are maximizers of HP over desired speed ranges) and then the dramtic factors, chassis set up, tires, driver, etc.
the torque at the engine is irrelavant, if we dont know the rpms. if we have the HP and it is the same, with all the driveline attached, all those factors you mentioned are incorporated in the rear wheel dyno number.

so, in the end, the curves show the relationship of two close to the same type cars, with the same power curves, but different torque values. you see that in acceleration modeling, there wont be much of a difference. can you find any??

Mk



Now,

tommytomaso

So why cant a 5L V8 928 s4 out shine a 3.6? inline6 M3?
I6 has a lighter internal mass....50 less Tq is nothing ..its all the small things that make up the diferance...lighter crank,smaller pistons...beter gearing per its weight.
...lets not forget BMW drivers are just beter drivers........hehehe

mark kibort

It can, but thats not the point. I think the upper limits of the 5 liter is near 600hp, while the upper limits of the 3.2 is near 500hp. (based on race engine specs)
internal mass isnt as much of a power factor as it is a absolute weight factor and a strength factor. this rotating weight has the effect of more weight as it was sitting it the car, but difference of 50lbs of crank from 5000rpm to 8000rpm over 5 seconds, has a power value associated with it. could be near 5-10hp or the same effect if 75 or 100lbs was sitting in the car. the difference of two different cranks is going to be much less.

the car can be lighter, and gearing is just the fine tuning that maximizes the hp available over a speed range.

In my races, the trade offs are very equal. so equal in fact, its not uncommon for a nose to tail race for the entire race! then, racing becomes a chess game, or a wait for someone to make a mistake! when ive been beat or have beaten one of these near equal hp/weight ratio BMWs, neither one of us have ever felt it was unfair. its all trade offs , the way racing should be!

MK

SharkSkin

Torqe is multiplied by RPM in the equation to find horsepower. The BMW revs higher so the torque is multiplied by a bigger number. Simple as that.