Area under the power curve

[-Josh-]

I was reading through one of my old Hot Rod Magazines and found some really good tech articles in the January 2004 issue. This one in particular i thought would be a good post since everyone's always talking about peak numbers on here. It's a good article for gear heads...


HR January 2004, pg. 46
Area Under the Curve

Notice we said "the rpm range where the engine spends most of its time." Merely considering peak numbers is misleading. In almost every case, it is better to look at the average area under the power curve rather than simply at peak numbers, because a broader, flatter curve generally delivers superior performance to a peaky curve. As superflow's Harold Bettes puts it, "Some engines have a power curve that looks like a table top instead of a mountain range in profile are pure pleasures to drive." Comp cams Scooter Brothers adds, "If its a comp elminator, pro stock, or Winston Cup car, maybe peak power is the answer," because these engines operate in a relatively narrow RPM band. "But for the dual purpose car, torque must be flat for an extended period of time."

According to David Reher, "We look at the average horsepower within the RPM range we run in; we dont look at the peak number. Anytime you can pick up the average, that's an increase. But you dont want to lose power somewhere else."

"The wider the powerband, the better the acceleration," says turbo wizard Ken Duttweiler. "The best exacmples are variable cam engines like the Honda VTEC - they'll pull down to 500 RPM and accelerate to 7,000!" And Norm Brandes at Westech Automotive (of Wisconsin) adds that high strung, peaky motors "are easier to get out of tune. A carb on a good 'torque' motor sees a much stronger manifold signal, so it's more forgiving. The same holds true with electronic engine management; the computer will be much happier with a broad curve."

Generally the RPM range that is most important is the area between peak torque RPM and peak power RPM. The car should be geared so that you shift 400-500 RPM beyond peak power, and the engine "falls back" to just beyond the peak torque point. Assuming a similar operating range, the engine with the greater area under the power curve between the power and torque RPM peak points makes for the better combination. On an engine with the most "area under the curve," the torque falls off less rapidly after hitting its peak, so in that sense you are always building for the best overall torque, in order to produce the best overall power. This is where Scooter Brothers of Comp Cams gets his axiom, "build for torque, and horsepower will take care of itself," but remember the end goal is always to generate maximum power within your engine's operating RPM range. "There's not one thing that isn't a tradeoff," David Reher points out. "That's the most critical thing in engine building: deciding where and when to make those tradeoffs." Harold Bettes adds, "It is teh package with the greatest area under the power curve that has the advantage. Remember, you cannot have horsepower without torque, but you can have torque without horsepower!" It's called a dumptruck. HR

[Mr. Luos]

How is this torque curve???
Would be even better if the damn thing was tuned.

[-Jayson-]

This is what my power curve looked like when i was completely stock. This isnt my dyno sheet, but done on a cavalier with the exact same setup as mine, the cavalier was stock when this is done. MMM you gotta love roots blowers.

[-Josh-]

Love it, everyone whip em out and lets compare.. dyno sheets i mean...

[Mr. Luos]

Jayson....no offense to that sheet, but it starts at 4,000 RPM's basicly. This doesn't really show power 'under the band.'

[TheStang00]

Originally Posted by Mr. Luos

Jayson....no offense to that sheet, but it starts at 4,000 RPM's basicly. This doesn't really show power 'under the band.'

but... it does stay relatively flat until 6200. when it shifts at the top of a gear it probably wouldnt fall much if any below 4000.

[-The Stig-]

Right Click, Save As...

You can see my dyno graph there... I'll look for the actual pictures of the dyno sheets later.

[Mr. Luos]

Originally Posted by TheStang00

but... it does stay relatively flat until 6200. when it shifts at the top of a gear it probably wouldnt fall much if any below 4000.

Expand the graph so it looks like my graph. It wouldn't look as flat.

Before anyone gets pissy about that statement, I am saying the dyno is a bad dyno. Just saying it isn't as flat as it looks.
My older dyno's looked better than the one I posted. Lack of tune kept that one from being a flat torque curve....

Lid and Catback dynograph....

[TheStang00]

Originally Posted by Mr. Luos

Expand the graph so it looks like my graph. It wouldn't look as flat.

Before anyone gets pissy about that statement, I am saying the dyno is a bad dyno. Just saying it isn't as flat as it looks.
My older dyno's looked better than the one I posted. Lack of tune kept that one from being a flat torque curve....

Lid and Catback dynograph....

yep u are right about it peaking later. for practical cruising purposes it could cause a problem. the first dyno u posted looks like it has more low end...

[Mr. Luos]

Originally Posted by TheStang00

the first dyno u posted looks like it has more low end...

Should have less. Most cams tend to do that to these cars. I actually picked up a bunch of power across the board.

You can kinda notice the difference in where the dyno operator started testing. That might be some of the difference you saw. The run in red started at 1250 RPM's, which is quite low. I asked him to, I wanted to see how much torque it had down there. Blue run is the same as the first one I posted.

[TheStang00]

Originally Posted by Mr. Luos

Should have less. Most cams tend to do that to these cars. I actually picked up a bunch of power across the board.

You can kinda notice the difference in where the dyno operator started testing. That might be some of the difference you saw.

yup thats probably the difference... show all my experience in reading dyno charts...

[mason_RsX]

Interesting stuff...When ppl I talk with tell me about a hp number Ill ask where it comes at, how big is the powerband?

Ive always said tho, a large powerband can compensate for driver error...You can drive a small powerband car, but you have to be an excellent driver, one poor shift timing and you out of the powerband and potentially out of the race...

The other thing is that torque without horsepower can lead to poor performance...look at diesels...oodles of torque right along the powerband, very little horsepower...and it has to be tuned magnificantly and have an excellent driver to perform

[-Jayson-]

well my peak torque hits at 2400 RPMS, yeah i know that dyno sheet isnt the best, its my buddies.

[nissanfanatic]

I personally don't value something that starts low with a bunch of torque, but rather something that doesn't fall out of power between shifts. I know of cars that don't begin making power until like 5k and peak power occurs at like 6k. So when they shift, they fall out of the powerband.

But I know I don't begin to make power until 4k and it makes good power to 6k at least. So When I shift, I end up right back at 4k for second and then 4.5k for the rest. Seems to work and I don't even come close to making boost in daily driving. NTM it hits like hell.haha

[-Jayson-]

i love my low end torque, its something im going to look for in every car i get. it just ads so much grunt to the car. You dont need much gas to accelerate quickly. My engine also doesnt fall out of the power band, the engine only redlines at 6500 RPMS. Also i really love my engine cause it hits its max torque peak twice, once at 2400 RPMS and again at 4200 RPMS. Thats what gives my car a really nice flat power band.