foolio

I think by now an engineer given the torque/rpm curve for an engine (and hp curve for convenience) can calculate the acceleration potential for a given mass. I don't like to debate physics with someone who doesn't like to do math.

The interesting point to me is the real-life significance of max torque figures. Why do we imagine a "stump puller" when we hear of an engine that has a maximum torque of 500 lb-ft?

I've come to the realization that:
torque has a rough correlation to engine size
=> the larger the engine the more expensive it is engineer it to rev up high (due to greater mass)
=> thus these big displacement engines are tuned for power low in the RPM range
=> and drag racing is all about the low RPM range

What do you guys think.

no_really

drag racing isn't about low rpm. The "best" way to make more power is increase the volume of air moving through your engine, and increase the amount of fuel that can be burned in a combustion event. The size of each explosion has a direct correlation to the amount of torque generated. If you increase the amount of torque your engine generates at a given rpm, you increase the horsepower at tht rpm. You cannot increase horsepower at a given rpm without increasing torque. you can spin your engine faster to stay in first gear longer, but you won't accelerate any harder in first gear, because you didn't increase torque.

foolio

You can also increase the amount of air + fuel combusted by increasing the speed of the explosions right? e.g. You double the explosions, you double your power. Think of a pulley.

cutes2k

Funny isn't it,

a Honda forum talking about Torque.

neko_cat

All I was trying to show is that the torque curve IS your acceleration curve.

If you increase torque on a spot on the torque curve the acceleration curve will match it there. So if you want to know how you accelerate look no further than your torque curve it is a good rough estimate of how you will accelerate in each gear.

Change that curve and of coarse you also changed HP. But when you discuss what relates to acceleration I think it's fair to say that TQ is more closely related as they match curves 1 to 1.


Nether is a more useful figure. I'm just trying to show people with a graph that indeed it is RWTQ that you feel pushing you back in your seat. Work takes on a completely different curve.

I think both are useful and I think Neither is more useful. It's so easy to convert back and forth that you can get one or the other at any point.

The only useful thing is looking at:
HP curve
TQ curve
gearing
weight
.cd

Without all of those any single one is pretty useless.

One could make a new number that used all of those to normalize performance of any car where you knew all of those.

That number would be a 1/4 mile drag strip.

It takes all of those variables and then some into account.

Though for fun you could make a new number that did the math to figure out RWTQ curves for each car. The car with that higher total RWTQ will be the quicker car. You could sample 1000 points across an dyno curve and sum them to arrive at the total. This would be a bit better than an average of the points.

If magazines showed TOTAL and AVERAGE RWTQ based on dyno curves
the ratios of different cars would be somewhat similar to the ratios of their 1/4 mile times I'd bet.

-mikey

Here's the 3 gear plot:

There's lots to see in it.

I got to about 85MPH before I had to shut down, out of room.
You can see drag's effect.
I only scaled everything to match the top once for the entire plot, not for each gear.

So the relationship of acceleration between gears is accurate. Acceleration drops from the mechanical disadvantage as well as from drag as time increases.

AlanP

So the driver of the low-torque car (e.g. S2K) needs to choose a different gear ratio than the driver of the high-torque car (e.g. Mustang GT). So what is your point? You've added absolutely nothing (but confusion) to this discussion.

To those of us who study the history of science, Isaac Newton was the first to advance the notion that simple, concise physical agreements are better than page after page of wild handwaving. Before Newton, philosophers like Descartes used to think that a longer arument with more words must be better. But Newton is considered one of the greatest minds of all time for his ability to distill physical ideas to the core.

Take a look at the fifteen pages of posts to this forum. You fill find that those who really understand what is going on can get to the point in a few lines.

If you know only a car's mass and it's peak torque at the crank (you are NOT given the RPM at which the peak torque is delivered), you know absolutely nothing about how well it will accelerate.

If you know a car's mass and it's peak horsepower, you know to a high degree of accuracy it's peak acceleration.

That's about it. Why 15 pages of posts?

Neko_cat- You can show in a few lines of algebra that the accleration curve is proportional to the torque curve. But that constant of proportionality involves the GEAR RATIO. That's why you could only normalize your curve in one area. The gear ratio changes every time you change gears.

neko_cat

If you think that I've added nothing to peoples understanding with the my visual graph than how much less useful was your reply?

I fully understand the physics going on very well.
I never spoke of using one point as useful for much of anything.
You find useful what you find useful.
Good for you.

-mikey

daabc

AlanP

"If you know a car's mass and it's peak horsepower, you know to a high degree of accuracy it's peak acceleration."

I"ll take that challenge. I"ll even give you RPM.

Car A:
2800 lbs
240 HP @ 40,000RPM

Lets see you try to "gear" this to get the same acceleration as the S2000, and consistently hit the powerband.

brockLT1

the more torque on top of a fair amount of hp is always a good thing, as well as keeping the torque flat and linear untill 5252 rpm, where it falls off.


so get a car with a lot of hp and a lot of torque i.e. V8's!!!!!!!

AlanP

In any given gear, the torque curve has the same shape as the acceleration curve (torque is proportional to acceleration in any given gear). That proportionality can be shown in five lines of algebra.

Who cares?

I'm trying to point out that your post, and your curves, have no bearing on the original question of whether HP or torque determines how a car accelerates. The constant of proportionality changes every time you switch gears. Your own curves show that you could only normalize the curves in one gear.