Who cares about torque! I drive a Honda that has 500hp and 1 lb-ft.

 

Rich,

No way in hell do I take any of these posts personally. There's are reason
I"m asking questions, and I'm looking up to everyone else to answer them.

My problem is, I'm a product of my surroundings. Getting good information
is sometimes tough; especially when half the world says one thing, and the
other half disagrees.

You will be happy to know, I am currently pursuing methods to return to school
at the University level for Electrical Engineering. Next week, I have an interview
with a senior Engineer!

I guess it's never too late to upgrade...would you believe car tech, the Discovery
Channel and people in this forum are my inspiration to take the next step.

P.S. I'm still going to try that second gear sprint and post the results.

 

Look at this torque curve:

http://www.jonaadland.com/NewPics3/Baseline.JPG

Look at this acceleration curve:

http://www.jonaadland.com/NewPics3/A...ion%20Plot.JPG

Striking resemblance....

You kids can play along at home, too. With WinPEP 7, load a dyno run without any funky spikes or anything. Unfortuantley it won't plot acceleration, but you can plot speed vs. time (you'll immediately get a clue by looking at the slope of the line--which is the very definition of acceleration).

Now, export the data to Excel. Make a column for acceleration (change in velocity divided by change in time). The way the program exports the data will give you a jumpy line. For the above graph I exported it in increments of .01 sec then smoothed the line a bit by doing a running average of the last 10 acceleration values (averaging them over a moving tenth of a second). Some Excel wizzes here ought to be able to give better tips.

There. For a given gear acceleration follows the engines torque curve proportionally (excluding aero, etc, which the dyno does nicely). Many of you have the data collected already and can see it for yourselves if you like.

Unfortunately, what usually gets lost in these discussions is just how meaningless the above actually is if you're trying to win a race.....

 

I used to be really into this whole rwhp/dyno/weight thing...thought I really knew what I was talking about....and in hindsight, I probably gave some wacky estimations...

But when I started working around my local dyno shop...and seeing a lot of cars and then finding out what they ran....I had to rethink my little theories.

Take my Lightning...it made 414/507 @ the wheels and weighs around 4700 lbs.

You can see the graph HERE

Every calculator I have says it needs to make around 500 rwhp to do that.

Then you have my brother's BBC in his Nova. It put down 442/530 @ the wheels and weighs I guess around 3100 lbs. The car I figure runs 10.5's@130 mph (it ran a 10.904@128.19 with some problems and leaving @ 1200 rpm).

Every calculator I have says it needs to make around 530 rwhp to do that.

I am not even putting into this aerodynamic resistance.

Just thought I would add my thoughts....

 

Rich said it best, and I'll add that maximum acceleration in any given gear is achieved at the torque peak, not the horsepower peak.

Engine torque, multipled by gearing, minus frictional losses is torque at the axles. Multiply by the radius of the drive wheel and you have thrust at the contact patch (tire), which is force (F) in the formula below. Divide by the weight of the car (m) and you've got acceleration (a) in g's*. Thanks Sir Isaac.

F = ma
a = F/m

*Frictional (rolling resistance) and aerodynamic losses are not factored in.

 

Where?

And I want to reiterate that maximum acceleration at any given speed is achieved at the horsepower peak, not the torque peak.

 

Sorry Kev, I know you didn't mean to type that...I just like using that emoticon.

He's kinda funky looking.

 

Why wouldn't he have? His statement and jimlab's are both correct.

 

Maximum acceleration at any given speed is seen when the gear chosen is the one which allows maximum torque to be delivered to the tire contact patch (ignoring effects of aerodynamics and friction).

Rich

 

Which is a ridiculous statement. It's the same as saying that maximum acceleration at any speed is achieved in the next lower gear, because torque at the axles at the horsepower peak would be higher than maximum torque at the axles (torque peak) in the current gear. Why not add that grass is green? Most of the time.

So... where's maximum acceleration in first gear when you can't downshift?

 

There^^^


And we continue to go thru it, don't we?

Let's open the other worm container: why do highend racers like Nextel Cup and Pro Stock go for higher and higher rpm even though hp isn't increasing, but rpm is? Or assume for the moment that peak hp remains the same but rpm increases 5%.

Even better, assume they lose 2% hp with a 5% rpm gain and go faster. 'Splain that to me.

 

Man, ya'll gotta go use the search thread and look for OldSStrokers previous posts on this HP vs. TQ debate.

My basic rule of racing is make the most TQ I can make at the highest RPM I can make it at and then multiply it as much as I can for the given track, distance and traction.

Bret

 

If RPM is increasing AND Horsepower is decreasing, then torque has fallen off
the deep end by forumla.


If a motor is rev'ing beyond the HP peak, it is losing all of the punch.

The only reason I'm aware of exceeding the HP peak is to allow for the next
gear to fall as high up on the HP curve. I've seen this referred to as
"straddling the curve".

That's my guess?

You will also find this thread EXTREMELY interesting.

http://web.camaross.com/forums/showt...highlight=peak

(EDIT - I just read most of that. Damn did I say some ignorant things. I even got the last word in! )

 

All other things being equal, more rpm means more wheel speed (and therefore more ground covered per unit of time) at the top of any gear, even if horsepower is falling off a little more.

In a high horsepower application, the difference in acceleration would probably be negligible and more than offset by the increase in wheel speed, especially if the power curve and gearing cooperated and you were still producing more torque at the axles at peak rpm than the maximum possible in the next higher gear.

Or, class or governing body allowing, you could run a little more gear and keep roughly the same top speed in each gear, but accelerate a little faster at any rpm in every gear, traction allowing.

 

You just proved my statement correct with your first paragraph.

As to 1st gear? Max acceleration is at the torque peak if you can't downshift. See? It's not hard...But if you COULD downshift, it would be at (or near) the horsepower peak in a lower gear.