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Discussion Starter · #1 · (Edited)
So I think I might understand what MikeK was talking about. After contemplating this and trying to come up with reasonable/logical answer, I think I know. But, I don't want to look like a dumbass explaining my conculsion if I'm wrong. So, in this thread can someone explain exactly what this means? I'm trying to pile enough information about building a motor and all you'll need to know. I have started a website with a shitload of nOOb information. I hope to have it up by summer. I know there is ser.net and all, but I'm trying to make this site very user / non reader friendly. As in having big letters and lots of pictures :D. And also having up to date information and products. Like Mike has been figuring out and stating lately...some of that info is outdated and doesn't make sense anymore.
 

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Basically, if a car makes more peak hp, but not until 8200 rpm it may be outmanned by a car that makes a more power for a longer time but does not have as high a peak hp number. The graph of a Civic Si starts out so low and then builds up to that peak hp. Our SE-Rs are quicker because they have a flat torque curve and they make more power for most of the rev range than an Si.
 

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this is where it helps to know about Riemann sums and integrals - check your math book or search google for a more in depth explanation

basically, area under the power curve pertains to the average power generated in a certain rpm range (ex: 4500-7700 rpm). You want the highest average power, so if you had [email protected] and [email protected] w/ a nice straight slope (no bumps or dips), that would be better than [email protected] and [email protected] (assuming again no bumps or dips). The latter power curve would have a sharper slope, meaning it would be relatively nutless down low, slowly building to nice topend power (like my B16). The former curve would have a less steep slope so it would have decent pull (and throttle response) thoughout more of the rev range, only being outdone at the very top (like my SR20).

then again it also depends a lot on how tall your axle is too - a short axle (higher numerical ratio) will allow my B16 to get into the powerband quicker, negating some of it's disadvantage - but also allowing it to fall off cam a lot easier - making it tougher to keep on the boil after a little drop throttle oversteer in the corners.

Basically, it boils down to personal preference. Things like having an LSD, good suspension and tires will affect how much power you can put down, which more often than not is more important on the track than what your power curve looks like. Generally speaking though, a fatter power curve i.e. more area under the curve makes it easier to drive your average car faster.
 

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Bjorn said:
this is where it helps to know about Riemann sums and integrals - check your math book or search google for a more in depth explanation

basically, area under the power curve pertains to the average power generated in a certain rpm range (ex: 4500-7700 rpm). You want the highest average power, so if you had [email protected] and [email protected] w/ a nice straight slope (no bumps or dips), that would be better than [email protected] and [email protected] (assuming again no bumps or dips). The latter power curve would have a sharper slope, meaning it would be relatively nutless down low, slowly building to nice topend power (like my B16). The former curve would have a less steep slope so it would have decent pull (and throttle response) thoughout more of the rev range, only being outdone at the very top (like my SR20).

then again it also depends a lot on how tall your axle is too - a short axle (higher numerical ratio) will allow my B16 to get into the powerband quicker, negating some of it's disadvantage - but also allowing it to fall off cam a lot easier - making it tougher to keep on the boil after a little drop throttle oversteer in the corners.

Basically, it boils down to personal preference. Things like having an LSD, good suspension and tires will affect how much power you can put down, which more often than not is more important on the track than what your power curve looks like. Generally speaking though, a fatter power curve i.e. more area under the curve makes it easier to drive your average car faster.
You had to bring calculus into this...you want power whenever you hit the throttle. If you are coming out of a corner and not in the powerband, you are going to lose speed. This is where it helps to have a flat torque curve and not a particularly peaky powerband.
 

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a flat torque curve is only going to mean that you have relatively constant acceleration - how high that actual number is determines just how swiftly your acceleration will be. A linear torque curve may be nice to balance your understeer/oversteer with the throttle, but having a car that takes a set and pounds out a torque surge post apex will rocket you out of the corner quicker (probably at the disadvantage of being slower pre apex though)

bottom line: different driving styles dictate which powerband will be more useful

as far as calculus goes, a quick look into a text book w/ a picture of what exactly an integral is would help explain exactly what power under the curve means. If anyone is intimidated by calc, check out a high school algebra book to find out what a Riemann sum is
 

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I can scan a page from my calc 4 book if someone can host it
 

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mYseRgOesvrOOm said:
So I think I might understand what MikeK was talking about. After contemplating this and trying to come up with reasonable/logical answer, I think I know. But, I don't want to look like a dumbass explaining my conculsion if I'm wrong. So, in this thread can someone explain exactly what this means? I'm trying to pile enough information about building a motor and all you'll need to know. I have started a website with a shitload of nOOb information. I hope to have it up by summer. I know there is ser.net and all, but I'm trying to make this site very user / non reader friendly. As in having big letters and lots of pictures :D. And also having up to date information and products. Like Mike has been figuring out and stating lately...some of that info is outdated and doesn't make sense anymore.
Actualy it was intergrating the area under the curve of cam lift over degrees of duration.

A fat curve has more area than a skinny curve given the same amount of duration and will make more power.This is the super simple way of thinking about it.

Fat curves come from fast opening ramps and slow closing ramps on the cam lobe. This is hard to engineer BTW.

Mike
 

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Discussion Starter · #9 · (Edited)
choaderboy2 said:
Actualy it was intergrating the area under the curve of cam lift over degrees of duration.

A fat curve has more area than a skinny curve given the same amount of duration and will make more power.This is the super simple way of thinking about it.

Fat curves come from fast opening ramps and slow closing ramps on the cam lobe. This is hard to engineer BTW.

Mike
aHA! I knew it! That's what I was getting at! I knew it wasn't really about horsepower but in the cam design.

I thought of this because of the thread where someone had those flat looking cams in the European race VE motor. I figured, if the valve is opened longer at a larger intake possibility (or outake) then it would produce more power. Versus a cam that just opened to it's highest for a slight moment then closed. Only giving it a short time to gain its maximum intake level.

However, what I didn't know was the ramps being setup that way. Are you saying that the open and close sides are different in length and angle? Something like open would be set at 5 while closing at 6. (Those #'s aren't ment to represent any certain measurement, just the idea).

Thanks for the reply. I'm looking mighty smart to my friends ;). Haha...

JasonQ


[edit]

Like this, right?

 

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Bjorn said:
this is where it helps to know about Riemann sums and integrals - check your math book or search google for a more in depth explanation.
My goodness... Don't remind me. Calculus 2 all over again.
Our SR20 motors is GREAT when it comes to area under the curve; but then again, I'm only use to looking at turbo SR20 dyno curves :D ....Before I put cams in my car, power would fall off dramatically after 68oo RPMs. Now that I have S4 cams, I bet I only lose like 2-3 WHP after 68oo RPMs.
It would be cool to find out what the area (our powerband) is if we could figure out the equation of our so-called line so we can integrate. We can compare who has the highest average area and basically discuss whose car is technically faster given the same conditions (i.e. same wheels, tires, weight, etc.) for everybody's car.

Manny
 

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Discussion Starter · #12 ·
Storm88000 said:
Our cars are 'great under the curve' and thats all you really need to know. :D
Actually...I wasn't talking anything about the power of our motor. But the cam designs for our motor. Not about power making before peak, I already know that. I didn't reply until Mike said something because I knew it was about the design when he was talking about how one cam has 'more area under the curve' than another, even tho they may have the same lift and duration. 'There's more to cam design than just that'...

I don't need to know this so I can go design some really neato cam. I'm just curious about everything and I feel I have to understand every bit. Everytime the big dawgs are talking about something technical I want to understand. So far I'm doing purty good. :D
 

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it's all the same. area under the curve is the same no matter if your talking cams, hp, whatever. Thats why I posted that link right away, you just have to imagine it a little and think about it and transfer the same idea to the other question and then you have the same answer basicaly.
 

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Just to throw another factor into the mix.....

Now that you have area under the lift vs duration curve sussed out, consider the amount of valve lift at which the head peaks in flow.

Your head may peak in flow at 11.5mm valve lift (arbitrary number) - so draw a horizontal line across the curve at that amount of lift.

The area above that line doesn't contribute to power - only the area below it. Therefore the biggest contribution to making power is achieved by getting the steepest possible slopes on the curve up to that peak flow line (within mechanical limits). This gives more area as the valve is opening, as it's closing, and more "dwell" time at the peak flow lift for the head.

Above that line, the valve is basically just turning around and you can only take advantage of that upper area by modifying the head to flow more at the higher valve lift (or maybe boosting).
 

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Xcel can give you a formula for a curve if you want to try to integrate for area on your dyno plots.

I doubt that you'll get the exact valve/duration curve data for the cams unless you measure them yourself - but this is only one step away from reverse engineering so be careful :tongue:
 

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ouch, feels like i'm in AP Calc all over again!!
 
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