Bader-X

iTrader: (2)

Voted Peak HP.

because 4k-6.5k is where the race at and what the car is seeing in the race (mostly from a roll race).... and pulling away in each gear is better than power under the curve beacause when I`m racing I don`t want the grocery store trip to be where I feel the power of the car while shifting from 1.5k-3k rpm.

PREDATOR-Z

Undercurve is under the intersection of HP/Trq curves (5252).

Marc 85Z28

iTrader: (8)

IMO the "power under the curve" arguement is so full of holes it's unreal. Why bother having impressive torque numbers at 3000-4000rpm? Those numbers are measured under WOT throttle conditions. The under the curve arguement assumes you are going to make that kind of power while driving around... NOT AT WOT! You can't compare WOT torque figures to part throttle operation.

PREDATOR-Z

Actualy, yes you can. The numbers delivered at WOT for dyno purposes are just the maximum potential of the valve events of that combo. Part throttle will reflect the same, but with less output due to less fuel/air.
Meanig, if your part throttle manners are good your WOT numbers will be as well.

WS6FirebirdTA00

iTrader: (33)

Damn right. I want something that is going to have some bottom end. A lot of people replying mid range have setups that are far from what they say they want.

Marc 85Z28

iTrader: (8)

Can you back any of this up with real world evidence? You are inferring that the part throttle numbers will mimic a percentage of the WOT numbers correct? I have no dyno experience with this, but I can say that a 40 ft/lb difference across the RPM range at WOT will not translate into a noticable difference at part throttle. Having 10% more power under the curve at WOT on an engine with a 400ft/lb average may be noticable, but 10% more power under the curve at part throttle will not be.

PREDATOR-Z

I'm a little bit of a cam affectionado, yes I can back it up

Marc 85Z28

iTrader: (8)

I'm familiar with your reputation... And no offense, but respected opinion does not equal fact. I'm really just curious to see the difference at part throttle - can you provide that?

schultzsj

iTrader: (1)

As most people have said, power under the curve is where it is at but it has nothing to do with the 5252 number. If you remember from your calculus classes, "under the curve" is actually the sum of what is under the curve - in this case power (or torque). For comparison purposes, the sum has to be taken between two selected RPM's and it equates to averge power (or torque) between these RPM limits. The problem with this is you have to select the RPM limits that you are interested in and this is where all the discussion is.

For example, my car has a 3400 RPM stall converter so my usable power range is about 3400 to 6400 (where I shift) in first gear. So, from a dig I want the best AVERAGE power (under the curve) between these two RPM's. If I have high, peaky torque/power I might have more HP at a certain RPM but I am likely to have less AVERAGE between these two RPM's and so my I will be slower (even with more peak HP).

Another example is for 2nd (and higher) gears. I don't know exactly what my RPM drops to between gears (and it varies for the different gears and tranny types) but let's say it drops to 4800 at shift. Now I am interested in the 4800 to 6400 RPM range where higher, peaky torque/power MIGHT also yield higher AVERAGE power.

So, the correct answer is ALWAYS power under the curve (average). The real question is, between what RPM limits do want to be concerned with. If you are running a 5000 RPM stall converter and 456 gears with a 7000 RPM shift point, by all means go for the high-end peak power. For the rest of us (i.e. DD's) a somewhat flatter torque curve (less peaky) is best, giving more average power under wider RPM limits - especially if you don't want downshift everytime you want moderate acceleration on the street.

A quick indication of less-peaky, power-under-the-curve (i.e. a flatter torque curve) that I have always used to determine how fast a car is going to be is the RPM between the torque and power peaks. If it is narrow (less than 1500 RPM or so), the car will be slower. If it is wider (2000-4000) the car will be faster for similar horsepower. Mercedes AMG cars are great for this - they often have HP ratings similar to, or even slightly less than, their competition but usually stomp them in acceleration trials.

Steve

PREDATOR-Z

We were talking dyno graphs

LS1rulz

iTrader: (1)

So does "under the curve" refer to a certain RPM range (like most people mean) or does it refer to a certain throttle position percentage (like some are throwing in for some reason)?

schultzsj

iTrader: (1)

So was I - you can't get horsepower and torque readings at all RPM's anywhere else. The only part you get elsewhere is the RPM range in which you want your highest "under the curve horsepower/torque" (i.e. average).

I am not sure what you were trying to say with your response

Steve

Louie83

iTrader: (3)

That's a pretty good way to put it.

I believe they were called Reiman sums (spelling?) in which you take the integral and it calculates the actual area underneath a curve. The bottom limit in the integral would be the RPM you start at (or the RPM it ends up at after you ship), and the upper limit would be the RPM you shift at.

I don't think too many people are on the same page on what the term "under the curve" really means. I've heard lot's of different meanings, but from an engineering stand point, yours really makes the most sense.

I think what most of the people on here look at as is "under the curve" means lower RPM torque and peak means peak HP. The bigger the cam, the higher up the torque curve moves, HP is a product of torque and RPM, so the peak HP is generally higher. Sometimes those bigger cams get their torque curve cut short because they run into the redline while still making decent power.

I think what most of the "under the curve" crowd is promoting are smaller cams over larger cams, because with smaller cams you will be able to fit pretty much the whole torque curve before redlining. Therefore, if you look at a graph showing the entire RPM range, that car really will have more torque under the curve. But like you said, what really matters is the area within the RPM range in which you have the pedal to the metal and are shifting like a mad man.

KingSumthn

iTrader: (4)

just think about it this way...unless ur planning on racing from a stop, peak hp will get the job done more often on the street becuase as long as ur not in 1st gear u can always downshift to get to your powerband. and once ur racing, theres no reason to ever be under 4500 rpm. from a stop ud have no chance tho with a peaky car. so what do u prefer roll races or from a dig?

Puppet_Master

Marc makes a good point. There should be an equation that relates rpm, power, and gear ratio. So people who are familiar with MATLAB can maybe help write code for this. Maybe something like:

%power_curve_model.m
power_curve = %put power equation here
torque_curve = %put torque equation here


%differentiate and set to zero to find peak torque/power
rpm_low = solve(diff(torque_curve));
rpm_high = solve(diff(power_curve));

%integrate power curve with respect to rpm from the preceding range
result = int(power_curve,rpm,rpm_low,rpm_high);


obviously this needs tweaking but y'all get the idea.

mchdg86

iTrader: (3)

Damn this is an old thread but I would rather have higher peak HP numbers for my application because I spend very little time below 5000 RPMs with my stalled auto. But if I had a M6 I would want better average power. So I think there is no better one, it just depends on your application.

DarkJuggalo

iTrader: (6)

under the curve, its what counts on the street

darrensls1

I vote for my peak power getting under Jessica Alba's curves

But for this boring topic I agree with Predator-z. I want BOTH!

N4cer

iTrader: (11)

Why does every other sucker say power under the curve matters? That's true whether it's peaky or broad and flat. As long as you have max power under that curve of the rev range you'll be in, you're good.

Even from a stop, you're revving higher. That's why we dump clutches and put in big stalls. Even "on the street".

And come on, prefer roll racing or dig racing? Roll racing is for ricers. That shouldn't even be asked on a domestic board with *****.

KingSumthn

iTrader: (4)

saying roll racing is for ricers doesnt make any sense. The fact is most of us spend more time having fun with our cars on the street than we do at the track, and whenever you pull up next to something worth racing on the street ur usually already moving. you cant always just get a light. Plus as many people on here know, if u are running street tires an Fbody with decent power is a bitch to get traction. that means a race from a dig is more like a who gets better traction contest, which is pointless. But theres no question about it once you go to the track theres no complaining about traction. You made the choice to go to the track so u gotta deal with it.