h8bumps

iTrader: (4)

Ok, another board member (350zfred5283) and I have been trying to figure this out for a few days now, with no success.

There has to be a way to calculate HP and torque from data logs. A data log would log time, velocity and RPM. Of course:

HP= (Torque*RPM)/5252

You should be able to use Δt, Δv and mass to solve Energy and Work equations, but we can't figure out the correct equations to use.

Nick, please post the formulas you were using.

350zfred5283

Yo 11,

Here are the methods I've been using. I must be making a mistake somewhere. I tried just evaluating 5th gear for h8bumps only because of the 1:1 gear ratio but it still seems we are off.

Also, you might want to post this in the tuning forums?

Can anyone shed some insight? See below:

Energy Method:

Given - velocity, mass, time

K = 0.5*m*v^2
P = ΔK / Δt = (Kf - Ki) / (tf - ti) (Watts)
HP = P(Watts) / 745.6999

Work Method:

Given - velocity, mass, time

a = Δv / Δt = (vf - vi) / (tf - ti)
F = m*a
d = (vi*Δt) + 0.5*Δa*Δt
Work = F*d
P = Work / Δt (Watts)
HP = P (Watts) / 745.6999

Newton’s Law Method:

Given – velocity, mass, time, gravitational constant

a = Δv / Δt = (vf - vi) / (tf - ti)
F = m*a
a = F / m = (550*g*HP) / (v*m ) (ft/sec^2)
HP = (a*v*m) / (550*g)

Late,
Nick

h8bumps

iTrader: (4)

Here are the data logs. One is 5th gear, which we were looking at because of the 1:1 trans ratio, but maybe wind resistance affects the equations. The other file is a 1st gear file, so trans ratio might have to be a part of the equations.

Hmmm, I had to zip them cuz I don't how to post excel files any other way.

350zfred5283

Um, how come no one has replied to this thread? Are we all not good at vehicle dynamics? Have you all just learned from cause and effect and not theory??

I'm wasted right now!

Who's going to Dick Scott Nissan tomorrow?

h8bumps loves CrAZy AmY!!!

Late,
Nick

plumpzz

iTrader: (10)

If you know the volumetric or thermal efficiency of the engine, its a bit easier. Finding volumetric efficiency is a lot easier than finding the thermal efficiency.
You also need to realize that the process is alot more complex than those simple formulas. It is not an ideal process, its at super high pressures (which further deviates it from ideal processes) and at high temperatures. There is tabulated data on thermodynamics of combustion engines, and the math is simple if you have a few temperatures and pressures.

http://www.engr.colostate.edu/~allan...e1/page1f.html

350zfred5283

Um, yea....you really need to know the volumetric or thermal efficiency of the engine...how many time have you needed this info on a dyno???

Nice try...NEXT!

Also, engine efficiencies are constants and are not the source of my problems when I look at the numbers after my calculations (I'm not off by a factor but by ?)...it's something else.

Seriously, some PHD come and call me out and not some undergrad.

Late,
Nick

push

iTrader: (3)

That's because a dyno is actually measuring the torque, your data log on the other hand doesn't.

350zfred5283

So then, why can't you extrapolate torque from V, t, and m????????????

Enron Exec

There are too many incalculable variables. Plus no two engines are the same. Just look at compression and leak down tests.

Tring to formulate an equation to compare against a dyno is not going to be cost effective because the data you need to log and pool would prob be in the order of 100's if not 1000's. The cost for all sensors and electronics would be ridiculous. Why do all motor companies have engine dynos for?

350zfred5283

Enron,

You never answer the question theoretically? Please explain via equation, proof, etc..? Why is torque data so much more valuable than velocity vs. time on a PID controller for the ECU?

Thanks!!

plumpzz

iTrader: (10)

ouch. Atleast I know how to do the math for finding it out. Theres no real easy way of doing this. Extrapolating the torque curve would be useless because you don't know how the flow characteristics change on the engine as RPM increases, no can you realy formulate a mathematical way to represent the torque curve for the entire RPM range.

I just reread ur information. You can find average power output but it won't be close to 'peak' hp from the curve.

A non-load based dyno calculates torque by measuring the voltage created by spinning the drum against an inductor and comparing it against a set of tables, and then formulating HP. (My guess, on how it works).

350zfred5283

But have you really done the math???? I have...why can't you use the velocity and the time and extrapolate the data then? We're getting data points of time, velocity, and RPM's...shoudn't we be able to get torque & HP? What is so different from a dyno?

plumpzz

iTrader: (10)

A dyno is taking several thousand measurements of voltage every run, and is making a graph whose data is all instantaneous. There is no extrapolating going on. Daistek dynos extrapolate data, and they're not concidered good tools for measuring HP.
Like i said, you can get the average HP for the operating range, or even the average torque, but peak HP is determined by the shape of the torque curve, which you can't get by just doing one calculation. You would have to do several to have the curve close enough to concider doing a peak HP calculation.

350zfred5283

The resolution on the Cipher software is 1 data point per 0.06 seconds approximately...that means, 16 data points per second...I guess that is not enough then??? Wouldn't a dyno see the same kind of error?

350zfred5283

Is everyone sleepin'?? I just took a ride in my Z... F all this talk about HP, I think I'm going FI tomorrow.

Late,
Nick

Enron Exec

The short answer is, you dont have enough data.

350zfred5283

BOO to ENRON!! Actually, BOO to Cipher!

The next question is, is there any software other than a dyno that has a resolution that we could use (other than mounting sensors and creating our own software) that could get us this data?

I thought there was something out there you could mount to your vehicle (I know I has and accelerometer built in) that can plot HP v. RPM's? That still gets me to believe I can get HP from my data...

Oh well...I'll never give up!!

Thanks to all...

Late,
Nikki Ree

h8bumps

iTrader: (4)

Now THAT'S a BS answer. What additional data is missing?

A sample rate of approx 16 times per second should be enough to calculate torque vs rpm - it's just a matter of finding the right formulas.

The data log shows time, velocity, rpm... vehicle mass is known also. At time deltas of about .06 seconds, the data will provide a delta v, and you can solve for acceleration. From there, I would think you could solve F=m*a to solve for the force the wheels are exerting on the pavement. Then, Torque=F*d, so since the radius of the tires is known, we should be able to solve for the Torque at the wheels. But the formulas aren't working, so I'm wondering if we have to use Work or Energy formulas. Work and Energy formulas are just manipulations of velocity, time, acceleration, mass... all variables (or constants) that are available in the data log.

So it CAN be done -- it's just a matter of figuring out which formulas to use. I was hoping someone had gone through this and found out which calcs to use -- it surprises me that with all the people logging data, nobody has done this!!!

350zfred5283

Prior to 1972 most American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross HP was measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices. Do you really think the instrumentation used at this time had a resolution greater than 16 times per second? Does this mean that torque RPM curves have been created just recently due to new technology of sample rate?

I'm with Mike, I think it can be done too.

Q45tech

Dynos usually sample the drum speed at 1/1000 second intervals and calculate drum acceleration over this interval. The drum mass [weight] is known very accurately.

Since most spec an accuracy of 1% you would need 100 x 10 or 1000 samples per second.

Due to slippage in drive train the engine rpm is not tied to the vehicle speed precisely.