OldSStroker

4 mph is significant: 3.2%. If you were turning more r's with the 4.10s you were getting closer to the hp peak. If you were turning fewer with the 4.10s you might initially have been over the peak. My guess is that your gear change was more than 3.2 % (3.97 or 4.23). What was the "before" gear? I'm guessing 3.90 or even 3.73.

The trap speed is basically a function of hp and weight. You put down about 3% more with the 4.10s. If you put down 550 rwhp thru the traps that went up to about 570. 500-700 rpm could do that. If you were to make additional gear changes up and down you might find a slightly faster one. Then the only way to go faster would be more power or less weight, assuming you don't change drag.

IMO, the .22 came from the gears. Did the 60 ft. times change with the gear change?

My $02

RMC

That's incorrect. Inertia dyno's first find HP then find torque from the HP. They know the inertial mass of the rotating drum along with the frictional drag of the bearings, the size of the drum or it's distance, and they measure its acceleration.

W=F*d & F=ma ---> W=m*a*d & 1HP=550 W * 1 second

HP=550*t=(m X a X d) / (t X 550).

Horsepower= (mass * acceleration * distance) divided by (time * 550)

Then find torque

Torque can be figured by multiplying the horsepower by 5252, then dividing that by the speed at which the force was measured.

Brake dyno's use a load to measure torque then find HP.

There's two different types and the prevalent one is the inertia because of lower cost and simplicity.

Highlander

Isn't work = Torque = Nm?

RMC

In a way yes but also no...you are right they have the same units and are nearly identical. But they are still slightly different

alpha = degrees x (pi / 180)
d= (alpha / 2pi) x 2pi r = alpha x r

Torque is defined as force times moment arm or:
Torque =F x r

Work is defined as force times distance traveled or
W = F x d

Substitute d for angular:
W = F x alpha x r

So torque and work have a fixed relationship that depends on the travel in radians:

W = T x alpha

This should show you that for a different radian you can have more work but not more torque.

edit: It also follows that for smaller angles traveleved you can have less work with same torque applied. For 1 radian the angle is roughly 57degrees and torque would equal work. For larger angles radians is > 1 and acts as a multiplier for smaller angles < ~57 radians are < 1 and less work is done for same torque.

Thus the two are similiar but not always equal.

Highlander

With that explanation you reach on why the HP constant is 5252

Still ... HP is not "measurable" its simply a calculation made...

Torque is a physical measurement.. Tq can be multiplied, hp not.

RMC

That's a bit silly to say torque is a measurement and HP is only a calculation. Torque is just another calculation just like HP.

Distance is a measurement, time is a measurement. Everything else is a derivative from those.

Torque is calculated with force. Force units are 1 kg m²/s².. I don't think you can measure square numbers with a ruler. You have to calculate them. It is a derivative from physical measurements.

ds/dt=velocity, dv/dt= acceleration Those are calculations. Or better known as calculus

And ya know why they use 5252, because that's when the angular factor is 1 and thus torque and HP are always equal at that point. Both HP and TQ are calculations. You can get to one from the other using two different techniques. When you take the inertia dyno (ie. Dynojet) you are finding HP and not torque regardless of what your opinion is.

So, if they calculate the HP first then they must calculate TQ from a given factor which is why they put a meter to get your rpms.

If it's a brake dyno they are calculating torque first then finding HP from that.

W= T * alpha T= W/ alpha you can calc one or the other first.

OldSStroker

That's a little confusing to me. Here's a pretty good explanation from "How Stuff Works".

(Torque x Engine speed) / 5,252 = Horsepower

The engine that makes 300 pound-feet of torque at 4,000 RPM produces [(300 x 4,000) / 5,252] 228 horsepower at 4,000 RPM. But where does the number 5,252 come from?

To get from pound-feet of torque to horsepower, you need to go through a few conversions. The number 5,252 is the result of lumping several different conversion factors together into one number.

First, 1 horsepower is defined as 550 foot-pounds per second (read How Horsepower Works to find out how they got that number). The units of torque are pound-feet. So to get from torque to horsepower, you need the "per second" term. You get that by multiplying the torque by the engine speed.

But engine speed is normally referred to in revolutions per minute (RPM). Since we want a "per second," we need to convert RPMs to "something per second." The seconds are easy -- we just divide by 60 to get from minutes to seconds. Now what we need is a dimensionless unit for revolutions: a radian. A radian is actually a ratio of the length of an arc divided by the length of a radius, so the units of length cancel out and you're left with a dimensionless measure.

You can think of a revolution as a measurement of an angle. One revolution is 360 degrees of a circle. Since the circumference of a circle is (2 x pi x radius), there are 2-pi radians in a revolution. To convert revolutions per minute to radians per second, you multiply RPM by (2-pi/60), which equals 0.10472 radians per second. This gives us the "per second" we need to calculate horsepower.

Let's put this all together. We need to get to horsepower, which is 550 foot-pounds per second, using torque (pound-feet) and engine speed (RPM). If we divide the 550 foot-pounds by the 0.10472 radians per second (engine speed), we get 550/0.10472, which equals 5,252.

So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second."


I think there are other things than time and distance which can be measured. In most brake dynos I've seen, a force (at some fixed distance) is measured perhaps with a load cell. Knowing the fixed distance, torque is readily calculated. Most folks call this a measurement of torque. I don't think that's far off.

RMC

Yeah I just skipped detailing all the angular conversions. 5252 is a bunch of conversions but equates to when the factor is 1

Which as I said there is one factor between the two that is multiplied to torque or divided by HP to get the other value. That's why when that value corresponds to 1, they are equal because T * 1 = W. That is why there will always be one value for RPM where torque and HP are always equal.

They are still both calculated and not measured directly, and can be calculated from each other with the one known factor that differs.

It's the varying angles and speed that give different values of HP and TQ.

Which you calculate first depends on what knowns you are capable of measuring.

NewbieWar

One HP = 33,000 foot pounds per minute, or 550 foot pounds per second. HP= Torque in foot pounds * RPM over 5252 Why 5252 you ask? Because 5252 = 33,000 / ( 2 * pi ). So that HP = ( torque in lb-ft * RPM ) / (33000 / ( 2 * pi ) ).

make sense?

Edit: Technically they are all calculateable...
torque is the calculation of force x distance

so since its a calculated value does that mean its not measurable?

RMC

Definition of calculate:
estimate a figure using mathematics.

You don't need equations to use a ruler. You just have to compare to a uniform standard.

In a loose sense of the word maybe they are the same but you can't get calculations without measurements. Calculations are essentially estimates based multiple measurements.

So really neither TQ or Hp are a single independant measurement, they are based on multiple varying measurements. Though as we get more advanced int he individual measurements we can approximate these with greater and greater accuracy which we now do.

It's wordplay when it comes down to it and not important.

However, I wouldn't say HP is not measureable and TQ is. I would either say both are measurable or more accurately describe them as both are calculations based on measurements.

I still tend to disagree that it is a measurement because when you say TQ of an engine you are actually using calculus and taking the sum of individual torques through the whole range of motion in respect to time as in RPM. So you actually aren't ever able to take one instance of torque in respect to an engine. You take it in terms of rpm which is summation of torques with respect to revolutions over a period of time. So no, given the choice I would prefer to describe summations as calculations and not one measurement.

OK this was fun, I'm done after this edit.. I got to refresh a lot of my memory from physics and actually apply it to something I like in the real world.

As I look at the issue I think these are some of the general confusions. HP outside of an engine is a description of work and time based on an expirement a long time ago where 1 horse can raise 330 pounds of coal 100 feet in a minute. That became a standard. So you have HP =Work(or F*d) over a period of time.

People think of torque at a simple physics level as T=F*d and so they assume Work =Torque ... that's not true but for only one circumstance which is what shows up at 5252 rpms in an engine. Also people seem to confuse a generic force as being equal to Torque. So they see W=F*d and think W=T*d

There's actually more to consider in torque calculations
(T = m*r^2 * derivative of [omega]/ derivative of time ) but it's been simplified to an instantaneous moment for the intro physics level to be able to ignore the angle calculations.

Oh and for inertia dynos they calculate the distance in the work equation which is fixed instead of variable like the torque equation. That's how they are getting Work value without using any torque values in a dynojet. They take the drums known constant moment of inertia, factor in bearing drag, measure the radius, measure acceleration. That gives work.. then all that's left to find HP is to factor in the time so it's basically a whole lot of those calculations summed up..which is why the computer allows an inertia dyno to get more accurate the better the computer. It's just summing a whole lot of Work values over very very short periods of time and keeps track of engine rpm to show when to stop summing the values and provide an approximation for that rpm.

If you notice also a TQ and HP dyno graph always has one value higher on the left and it becomes the lower value on the right after they cross. That's exactly where the W= T * alpha comes in. For alpha >1 torque will be higher than Work done and for alpha<1 it will be lower. When you consider this over a time period the equation gets messier with conversions but that fundamental equation is still there and clearly evident.

You don't have to have torque to find HP if you use a work over time equation where the distance in the work equation uses arclength.
Respectively you don't need HP to find torque.

You can of course derive equations where they both are part of the equation, which is ultimately how each one determines the values it wasn't initially calculating.


That is all...good info discussed guys, thanks.

********************************************
Now here's the definitive answer straight from Dynojet themselves.

Q: Will the second dyno show a loss of horse power caused by the 3:27 to 4:10 gear change?

ANSWER:
Yes

EXPLANATION:

"The 4:10 gear will show less horsepower than the 3:27. The reason is due to rate of acceleration changes. The rate of acceleration is quicker with the 4:10. The horsepower will show less because the targeted RPM is met before the horsepower has a chance to overcome the rotational mass (dyno, drive line, etc.) or moment of inertia in speed.

******************
Which also shows that dynojets use acceleration of the drum, and it's rotational mass to calculate HP independant of torque...

Highlander

Of course they use rotational mass... that is important in calculating the HP!

Anyways... Tq can be measured.. easily.. use a dynamometer! and not a chassis dyno as we are talking about.

Remember torque wrench?

RMC

Yeah I realize both are possible and both can be independantly calculated from each other given the proper dyno. Whether you call it measurement or calculation depends on how specific you are being. Both use some slightly advanced physics and calculus though so I don't consider it a simple measurement.

I think many people don't realize that there are two different types of dynos that measure differently and that the common Dynojet actually measures HP first....

And if you want to simplify it like a torque wrench of course it is a very simple calculation. But that's my point. Whether it's a torque wrench or a horse lifting weight both calculations are easy.... it's the fact that it gets more complicated when rotated and measured over time.

It really shouldn't be oversimplified with elementary physics equations as people keep doing. Torque in respect to rpms in an engine isn't the same formula as T=F*d as you would calculate torque from a 12" wrench.

Highlander

I can put a long tube on a torque wrench and still measure the same torque.. why? because it has a dynamometer inside...

My dynamometer statement is a regular dynamometer that uses a spring to measure it.

marshall93z

while you guys are discussing physics and stuff, i am once again going to say that "a higher numerically numbered gear will show LESS hp on the dyno"!