Power Band

[muscle_Car1]

^:thumbup:

[blkfordsedan]

Side note, I have been at the dyno when a few cars have dynoed and their numbers did not cross at 5250 rpms...

HP & Torque will ALWAYS be the same at 5250 rpm. It is a law of Physics!

If you follow the HP vs Torque equations on the website Jim gave the link to, you can see how it works out. From a formula standpoint, as RPM increases, torque decreases, IF the HP remains constant. This is to satisfy the equation and is evident in the case of electric motors and mechanical speed reduction (like gearing or belt drives). Internal combustion engine are a little unique because HP is variable and dependent on volumetric efficiency and as RPM increases, HP increases to a point then takes a nose dive as you pass the effective breathing range. (they just run out of breathing capacity to support the required flow)

As for the RPM of peak HP and torque, it depends on the design of the individual engine. Head flow, camshaft profile, intake design, compression, (you get the idea), all effect the HP & torque curves.
It is safe to say that MOST stock & good street engines will have peak HP around 4500 to 5500 RPM and preferably a semi-flat torque curve with peak torque around 2200 to 2700 RPM. When you add long duration cams, single plane intakes, big port/valve heads, etc., you trade the flat torque curve for a narrow torque curve with a higher peak torque. This is OK for a race engine where you can keep the engine within the narrow range, but impractical for everyday use. This is important to remember! You can do a mod (like an intake or cam swap) that may not add much PEAK HP or Torque, but if it adds 3 or 4 HP and 5Lbft of torque across the entire RPM range (like 2200 - 5500) then your car will be faster than a mod that adds 10HP @ 5500 but adds nothing (or costs you torque) below that.

[smokeshow]

I have not read this article on this, I am just speaking from experience and seeing things on a chasis dyno and their wheel numbers. That being said I think I got a little of topic from the original post/thread...

If I get the time, and the dyno is free'd up, I will see if I can throw my n'Fest-ation on and see where the hp starts to take a drop in each gear. But those are two huge if's..

[pwgus]

another thing about the 5250 rpm equilibrium theory is, it sounded to me (and I could have misinterpreted it) like they were talking about HP and torque at the flywheel, while I believe most dynoes use HP/torque at the drive wheels, which is after the transmission, so wouldnt that throw things?

[smokeshow]

Yes, scaling the graph does alter numbers, but mainly that just changes the percentages of the numbers/load perimeters.. but in the cases of the cars I noticed, they all had cam swaps... my guess is that they weren't in time with each other...

[schaefz28]

Side note, I have been at the dyno when a few cars have dynoed and their numbers did not cross at 5250 rpms...

It is likely that the HP and TQ were scaled differently on the graph. At least this was the case both times I have had my camaro on the dyno.

[pwgus]

wow, all so interesting, thanks to everyone so far on these most informative answers. And that article is certainly very fascinating. Something to think about for sure. When I think about it, alot of it makes sense, but I seam to be specticle that 5250 is going to necessarily going to be magical for all engines, the fact may be true, but I doubt its a sweet spot for all engines.

[bhazard]

I never had a problem with wheelspin in my b3 festy. Unless I dumped the clutch. Even then I quickly found traction. Maybe it was the 175/70/13's.

The B6t is another story. Just hit the gas in first and the back end squats and the front tires go byebye.

[smokeshow]

My mistake on the extra 5 hp... For some reason, I could of swarn somewhere in my manual it said it had 68 hp.. nontheless, its not a powerhouse motor to say the least..

Side note, I have been at the dyno when a few cars have dynoed and their numbers did not cross at 5250 rpms...

Another side note.. Driving a FWD car and getting the max potential out of it is harder than it seems.. You have to shift at the right time and account for wheelspin... and factor in that the wheelspin is what is helping achieve that current rpm, and try to maintain it in between shifts is really hard to do in a low torque vehicle... I.e. Festiva... It can be done.. just not easily...

[bhazard]

Because 39 mpg aint that great, Im doing better than that with my B6t...

And driving "hard" to keep up with dodge caravans just embarrasses me.

I used to think my B3 was peppy. But the only real time I was trying to pull on someone I lost. It was an automatic neon.

Sure, it is peppy... compared to a 1.0L metro.

[Festiva_tunner]

Take advantage of it by shifting at 2000 rpms and doing the speed limit. You'll get awesome gas mileage.

Thats the whole point of the B3.

You'll feel accomplished when youre getting well over 400 miles out of your 10 gallon gas tank.

Why not take advantage of its reliability, and durability while having fun with it and only suffer a 5 mpg loss and still getting 39mpg on mixed driving with a lot of back country hard driving and wheel pealing through the city.

[Pu241]

Now that makes sense!
Think we might need to copy, with permission of course, and make this a sticky in a tech section or something similar.

I had heard this before that the torque and HP crossover vs RPM was always at a specific RPM. Even heard people say that's how you know the dyno run was real and not faked. But never got a good explanation as to why.

Thanks FB71!

[FB71]

John, here's a great explanation of HP vs TQ, and why 5252rpm is the crossover;

http://www.revsearch.com/dynamometer/torque_vs_horsepower.html

[Pu241]

Someone has posted a Dyno run of a B3 somewhere on this site.
I'll see if I can find it.
BTW, OEM B3 is only 63 HP.
How is it that you can predict the crossover of the HP and torque curves vs RPM (5250 rpm)?
I would imagine new OEM engines would show a clustering about a specific RPM range for the crossover, and as they age and maintenance varies the crossover would start to spread out over a larger range of RPM's.
Just interested in an explanation.

[iceracerdude]

The max power is where the max torque curve is as stated by the factory RPM number usually. I don't remember now but In the case of the b3 they claim it's at what, like 4250 rpms? That's why the max power is never the same as the red line number.
You're on the right track here as far as your questioning goes, a lot of people assume the max power is at redline. So the answer is the same for what ever engine you happen to be working with, whether it's for a "race" or "economy" application...so good question.