From a question that popped up in THIS thread:
MrMoe on Mar/01/10 said:See this is the part that confuses me. In the world of FI, what does it matter if one motor flows better at higher revs if they are making the same amount of torque? If torque is used to make HP and both motors share the same torque is there really an advantage to having more HP?
Of course. If one setup is able to carry the same peak torque longer, it is going to be faster.
Think about it: HP=TORQUE X RPM / 5252
So a car making peak torque of 100ft*lbs at 3000RPM that carries it to a 5000RPM is going to make peak HP of 95.2HP at 5000RPM.
Now take another car with the same weight, same drivetrain, etc makes the same peak torque at 3000RPM, but carries it to 8000RPM. That car will make a peak HP of 152.3 at 8000RPM, and is going to be faster, even though both cars make the same torque. They just make it at different points in the powerband.
Look at every dyno printout. The Torque and HP curves will ALWAYS intersect at 5252 RPM. That is not by accident. It is where 1 Ft*lb of Torque is Equal to 1 HP. one is a measure of rotational force (ft*lbs), and the other is power (1 HP=745.7 Watts=745.7 N*m/s).
A quick example:
The B18B makes peak power of [email protected], but peak torque is at an entirely different place in the powerband: 127 ft*[email protected]
So how is this possible?
The car makes peak torque at 5200RPM, which produces 125.74HP if you do the math.
But at 6300RPM, it makes 118.4ft*lbs of torque. So even though there is less torque being produced, the fact that that torque is being produced at a higher point in the powerband means that the motor is putting out more power (Work/time), which means that more work is being done. (Really that work is being done at a faster rate.)
So even though HP is more or less the golden standard in turbo selection, it can be misleading. The real best way to go about turbo selection is to think about what type of torque curve you are after.
If any of that confuses any of you who have never taken a physics class, here is a quick guide:
(where θ is the angle between the force vector and the lever arm, which is exactly what it sounds like)
Work=Force*Displacement (think energy transfer over some distance caused by a force)
Power=Work/Time (or the rate that work is being done)
You can get crazy with these equations, and derive infinitely more complex equations from them, but the equations provided should be enough to provide enough background info to understand exactly what HP and Torque really mean.
And Malhon lets keep things like angular velocity, and any and all Calculus out of it. I think these are sufficient.
Here is some proof. The math is pretty easy to follow:
Quote: sgtmillhouse648 on Mar/01/10 Quote: Danny50 on Mar/01/10And Malhon lets keep things like angular velocity, and any and all Calculus out of it. I think these are sufficient.
bbubbububbubbbuut this is the perfect app for conservation of angular momentum rate form
this is actually starting to get into the good ol' MD "Which car is quicker" discussions that used to take place! The big thing that you started to shine light on is the powerband aspect. the primary part of this then is not only placing your powerband where you want it, but also making sure that where you want it coincides with the gear choices and what kindof event you plan on competing in.
Quote: MichaelDelaney on Nov/30/02a powerband is the longest rpm range that has the highest torque (+/- 3 lb ft which is the error of measurement variance in a chassis dyno).
So here we have ITR cams in a properly fuel tuned 11.5 CR B18C1 engine vs. the same engine untuned.
Now, oNLY look at the torque curve.
Ignore the hp curve (here's why we emphasize TQ and not HP here on TI.)
The ITR cams have 2 different powerbands (untuned from 6200 to 7500 rpm and tuned from 5300 to 7400 rpm ) .
The torque is at the peak level or near the peak level (+/- 2-3 lb ft) . It runs for 2100 rpm in width tuned vs. a narrower 1200 rpm untuned.
They have different powerband locations and width. When we say "higher powerband location" we don't mean the torque value is higher. We mean the peak torque for that engine begins at a higher rpm and it's entire range is at a higher rpm.
in a nutshell:
WHERE YOUR PEAK TORQUE IS LOCATED ALoNG THE RPM RANGE IS IMPORTANT because it must be aligned to where your tranny operates.
Your tranny works within a certain 2000 rpm wide window usually when you are at full throttle. Sometimes to go faster, you want the engine powerband (peak tq) to line up with the tranny rpm window perfectly and sometimes for traction reasons you want the powerband to be staggered or delayed from the start of the tranny's rpm window.
You can't just look at a dyno sheet without considering how it relates to the tranny. If you don't consider this, you will see that a car has a great dyno sheet but is slow at the track. This explains why. Everything is inter-related and not an island onto itself to work properly.
Here is Erick Aguilar's record all motor 2.1 L B18C1. The powerband is from 6500 to 9500 rpm on the torque curve. Notice how nice and flat it is and how wide it is. 3000 rpm in width! that is a result of amazing packaging AND tuning combined .
Most of us are happy with a 2000 rpm powerband width which is the average.
You can determine or shift the powerband up or down the rpm range (for your given redline) by choosing the correct combination of parts with certain dimensions and by tuning (eg. cam gears, valve lash, ECU reprogram).
Some parts are designed (dimensions and layout) for an upper rpm powerband (6300-> redline) and others are designed for midrange (3500-6000 rpm).
Don't think that you can mix and match midrange powerband parts with upper rpm powerband parts to get an ultimate wide powerband.
When you combine a midrange powerband part with a high rpm one, they just cancel each other out and you get LESS power and a narrower powerband. Some novices just do this without knowing it because they don't understand the effect of a part's design and sizing or specs on powerbands...and end up buying parts that cancel each other's gains. Why? because they never were explained what a powerband is and why it is important.
you will see later on that the engine powerband must also match where your tranny's gears work in order for you to go faster than the other guy/gal lined up beside you. But we won't get into that now. Let's just take a breath and absorb this idea of a powerband as a guide for how you select engine parts.
it's not a stupid question. Some supposedly "advanced" people don't even get this concept.
As far as picking which setup to go with for whatever event you plan on choosing, let's compare autox to road racing to drag racing...
In the bulk of autox's i've been to, you really floor it through 1st, get into 2nd and stay parked there the bulk of the time. You end up a lot of the time in the 2k-(6-7)k range or so. Coming out of a turn at 2500k really doesn't do you a whole lot of good when your turbo hasn't spooled yet and won't (starting your powerband) till 3k-3500rpm. This is why on a small cramped track, a well pieced together supercharger or even an NA setup (but nobody cares about those no boost guys ) will outshine a very well pieced together turbo setup on a small track. A turbo just can't compete with needing the powerband to start at 2krpm.
on the other hand with road racing/drag racing (drag racing especially) the bulk of your time when you are accelerating is spent north of 3-4krpm. It's pretty easy to see here that a well pieced turbo setup will be much more efficient in these higher revs than a comperable supercharger setup.
So in summary, pick your event->pick your powerband->pick your goals (tq, not hp)->pick your setup
Check out this thread which goes over picking the proper turbo for your goals.