ericgrau

iTrader: (1)

I know I'm gonna get some flames for this, but there seems to be a widespread lack of understanding about torque.

First let me say that I think the LS1 is great. It delivers lots of power. I am not here to bash LS1's or V8's.

I am just going to cover some simple physics. Ideally everyone would learn this in school but that doesn't always happen.

A gear trades torque for rpms. If you have a 2:1 gear ratio, for example, it will double your torque and half your rpms. Sweet, free torque, right? So why not make cars with 10:1 gear reduction for ridiculous torque? Well, having thousands of foot-pounds of torque doesn't help much if your wheel can only spin at 10rpm.

That's where your transmission comes in. It lets you choose a gear for maximum torque at your current wheel rpm. At first this is your lowest gear, which provides maximum gear reduction. As you gain speed you are forced to upshift to keep up with your wheel rpms. For maximum power you ofcourse upshift as late as possible to get maximum gear reduction.

Okay, let's say you have an engine spinning at 2000rpm, producing 200 ft-lbs. of torque. That power goes through your tranny, which converts it to - for example - 500rpm and 800 ft-lbs. of wheel torque using a 4:1 gear reduction. Let's say you have a different engine spinning at 4000rpm, producing 100 ft-lbs. of torque. The power goes through your tranny, which converts it to - for example - 500 rpm and 800 ft-lbs. of wheel torque using an 8:1 gear reduction. The 2nd engine gives you the exact same results!

So as you can see, 100 ft-lbs. of torque can mean just as much as 200 ft-lbs. of torque given a high enough rpm. So how do we get a good measurement of wheel torque? This is where horsepower comes in:
So in the above example:
As you might have guessed, the two engines produce the exact same horsepower. So does either engine have any advantage over the other? No, none at all. They both accelerate at exactly the same rate.

Having high torque does not mean your car is faster. Wheel torque is 100% dependant on horsepower

So what's the point of torque? Well, if one car has 200 ft-lbs. of torque at 2000rpm, it is obviously faster than another car that gets 150 ft-lbs. of torque at 2000rpm. 200 x 2000 > 150 x 2000. Plus if you ever look at a horsepower dyno chart, it's hard to figure out if the car has any low end power. Every car seems to have maximum power at high rpms, because higher rpms increase horsepower. But if you look at a torque curve, it removes the rpm advantage and makes low end power easy to see. Looking for a flat torque curve is easier than trying to figure out exactly how steep your horsepower curve is. Saying "That engine has good low-end torque" is the same as saying "That engine has good low-end horsepower". But since you look at torque curves to figure out low end power, we say the first statement, not the second statement.

What does this mean for rotaries and LS1's? An N/A rotary has "poor low end torque", which means it gives unusually low horsepower at the low rpms (even lower than what you'd expect, since all cars produce less power at low rpms). A twin turbo rotary (the stock FD) alleviates some of this problem using the smaller turbo to provide better low end power (or "low end torque"). A rotary with a large single turbo might magnify this problem due to turbo lag. And the LS1 gets good power across the entire rev range; it gets less power at low & mid rpms than at high rpms, but that's to be expected. It's low end power isn't unusually low like a N/A rotary.

So hopefully when comparing one dyno chart to another, everyone will now compare peak horsepower and use horsepower in the left half of the chart to compare low end power. And hopefully nobody will quote torque numbers anymore, unless comparing an LS1 to an LS1 or comparing a rotary to a rotary or comparing two engines with the same rpm limit and with peak torques at the same rpm. Otherwise it is best to quote horsepower numbers only, because that will be the only thing that determines wheel torque.

NOTE: Don't confuse "Wheel Torque" with torque numbers measured at the wheel. Just as your wheel is not spinning at 5000rpm, so also the torque numbers on the dyno do not equal wheel torque. They equal engine rpms and engine torque, minus drivetrain losses.

carsaregood

i'm not sure i understand your argument when you say that we should talk about horsepower, not torque, because they are related, and can be derived from each other:

hp = torque x rpm / 5252

oh i just read your note at the bottom. is your point that a car's performance is highly gear related?

good post man, a fellow hb inhabitant.

ericgrau

iTrader: (1)

There are explanations around the statement that tell you why you often can't rate performance with torque numbers. In rare situations you can, but usually you can't because redlines, trannies, etc. are different.

jimlab

Wouldn't the same apply to horsepower?

The correct answer is that you can't accurately predict the outcome of a race simply by comparing two peak power numbers, two power to weight ratios, or two power to displacement ratios.

The rate of acceleration of a vehicle is determined by its torque curve, gearing, and weight, as well as rolling and aerodynamic resistance and the coefficient of friction at the contact patch.

F = m * a, where F is the net force with all factors considered, as mentioned above.

Obviously not.

https://www.rx7club.com/showthread.p...ghlight=torque

So, how many times were you planning to start the same thread over again?

GtoRx7

iTrader: (5)

Ah, yet another person that truely understands. I had this argument with many, and most say torque is the only real important factor, and higher rpms just save shift times. They forget a force needs time to accomplish work.

razorback

so what made you upgrade to a 3 rotor?

ericgrau

iTrader: (1)

Sigh... I wish our schools taught physics thoroughly, and flunked people who forgot it all 3 months later. But no... standardized tests are unfair, they say. I'm not liking the alternative.

In America, truth is what we want it to be. I mean, seriously, people just make stuff up or hear it from a buddy. Then they get mad at you for not agreeing. Whether or not his side is justifiable or your side is justifiable isn't really an issue anymore. I mean I try "A leads to B leads to C because of E and F", and that proves it works by the indisputable laws E & F by which our modern world runs. Then somebody says, "Nah, it's this way" or "Why can't it also by this way?" or "I'm sure that other way would work too" or "last time you said G leads to H and G sounds like C so I'm not listening to you". I'm not giving my opinion on ice cream flavors here. This is real physics, honest! It's basic physics. It's not complicated. I've done much, much harder work in my physics classes. I got an A. Any 15 year old student who just took the class should be able to tell you this. This is like trying to convince kindergarteners that heavy objects fall at the same rate as light objects.

You know what... screw it all.

P = Tw
T1w1 = T2w2 or T2 = T1 * N, w2 = T1 / N
F = T / d
F = ma
T = torque, w = rotational speed in radians per second, F = force, d = wheel diameter, m = mass, a = acceleration

Here's your equations, now you figure it out for yourself. And in the mean time don't believe anything you can't justify.

razorback

so this is your subtle/retarded way of bashing v8 swaps...

ericgrau

iTrader: (1)

Yes, that's exactly what it is. You're clever... you figured me out just by saying so

slo

iTrader: (1)

What wins races is the better set up race car optimized for particular event, and set up to the maximamum a racing class will allow.

You also have to look at more than just peak HP, HP over a range is far more important. Even 13b's arent nescisarily that bad at making HP over a range of several thousand RPM's, its just not going to be down low, and it will have an upper limit thats determined by porting and turbo's at which point gaining more HP up top is narrowing the effective power band.

Comparing a 5.7-6L engine to a 2.6L engine is a pointless loosing battle for the smaller engine. It doesn't matter that the engines are of a different design. How well would a 4 rotor rate against a 2.3L 4 cyl.

razorback

well everything else has been tried. the weight argument, handling argument, i guess the next logical route was to say something has too much power...

things in the real world do not always work out with the same predicted outcome as on paper, there are other determining factors.

ericgrau

iTrader: (1)

Forest for the trees, slo.

Razorback: Ya, you can make a 100HP, 4000lb. car with a 0-60 of 5s if you just engineer those, um, other factors.... a lot. And hard. Better work overtime.

wingsfan

More or less. As Jim pointed out he's attempted the same argument in several threads now.

ericgrau

iTrader: (1)

Link 'em.

slo

iTrader: (1)

so I suppose the LSX miata I am planning is going to be really slow then. Why post this here in this forum if your not attempting to bash V8 swappers. Your making us rotary guys look bad.

wingsfan

At least three, including this one.

https://www.rx7club.com/showthread.p...ghlight=torque

https://www.rx7club.com/showthread.p...ghlight=torque

ericgrau

iTrader: (1)

Slo:
Ok, quote where I said/implied the LS1 is/would be slow.

Tell me where else people talk about torque.

Wingsfan:
Since I've been to this section of the forums 3 times. I'm gonna have to say 3, total.

So you're telling me in all 3 of these threads I sung the praises of the LS1 on high? What did I say? At least tell me that if you're not going to give direct quotes.

razorback

those top fuel guys are really slow with all their torque

ericgrau

iTrader: (1)

Ok, that's the problem. I told everyone torquey cars are slow. Care to quote that?

You know, I once say a 3 rotor turbocharged RX-3 with old-faded paint, dings, etc. Guess I'm saying all beautiful cars like Ferraris are slow too.

You know, I could just be saying that horsepower is the only thing you need to look at. High torque or a high redline can help increase horsepower, but having high torque or a high redline doesn't necessarily mean anything. But having both does.

wingsfan

Who said you claimed they were slow?

Of course you did offer this doozy
https://www.rx7club.com/showpost.php...1&postcount=10

ericgrau

iTrader: (1)

And, care to embellish? I must be slow so you'll have to humor me.

Here's the section underneath that title fragment:
'cause that's the section where I said the LS1 is faster than the FD by all measures. I even included the sentance that could be misinterpreted, in case you want to use that. It's the 1st sentance.

razorback

i like that quote.

funny, i thought horsepower was a function of torque and rpm...

wingsfan

Clearly you're slow, otherwise you wouldn't feel the need to start a thread on a topic that's already been thoroughly explained to you.

wingsfan

No, the problem is that you started a polemic thread in the OEC section that has zippo to do with engine conversions.

ericgrau

iTrader: (1)

You quoted that from the section that said you need both torque and rpm to determine horsepower. If rpm is different you better not be quoting torque, because the same torque will give two different horsepowers.