And the dyno is using kinematic equations to calculate the force being applied to the drum by the vehicle wheels, right? Same equations can be applied if the vehicle is moving (Force @ pavement is accelerating the vehicle) if the vehicle mass is known.

How does the dyno account for this? The dyno is measuring force at the drum, and engine RPM, both as a function of time -- same as data log.

A larger # of samples per second would only increase resolution, or accuracy, of each data point. If a 5th gear run to redline takes, i don't know, 10 seconds, 160 data points (16 per second) should be plenty to show a HP and torque curve over the RPM range.

 

do you know:

precise mass of vehical? Think fluids, driver, any mods, etc.

drag coefficient of your car? consider altitude of your test, temperature, humidity, wind speed and direction

how was your traction? did you floor it without spinning the tires at all?

These are just some of the points where a dyno has an advantage. I'd say go spend the $60-70 and do a dyno pull.

 

I guess you don't understand how a dyno works. It uses electrical signals to measure the acceleration of the drum. Its not average acceleration like you are measuring, but instantaneous acceleration. It knows the mass and radius of the massive drum, finds the amount of torque applied to the drum, and then finds the HP in correlation to RPM. HP is a function of torque and RPM, so you need to know both. If you have 16 data points/sec, and a dyno run takes 10 seconds to accelerate from 2000-7000 rpm, then youll have 160 data points, at each of which you will need to find acceleration (320 calculations), and at each of those points, find the torque (320 more calculations), and then at each of thosepoints, find the HP (320 more calculation). Then graph the data, and pick the highest data point. Thats ur peak HP. Its not hard, and I dont know why you keep asking this stupid question

 

"Instantaneous" acceleration is just a fancy term for "acceleration over a very short period of time." The shorter the time period, the more accurate the calculation.

So, it should be possible to compute HP from acceleration, weight, and RPM. Hey, my GTechPro calculates it, even though their numbers will be a bit lower than a stock dyno because of the addition of air resistance (drag).

 

It's obvious you don't have a background in kinematics. If the topic is beyond the scope of your knowledge, please don't bother responding.


For everyone else: I'm positive that a HP vs RPM curve can be calculated from the data included in the data logs. I'm looking for someone with enough knowledge of kinematics equations that can help figure out which formulas can be used to calculate torque at each time interval in the log.

 

You're right, I dont. Its just the thing every student in every science major covers 2 weeks into physics 1. You have the formulas fool, find data points, and calculate it yourself.

And wtf is a background in kinematics? Ive taken quite a few semesters of physics, and I don't know what that is. Kinematics is just that, 2d motion. So stop using big words to make urself feel smarter. What you have to do is find instantaneous acceleration at each point, then find the torque on the wheels from the 1:1 ratio in the transmission and then find HP after that, and find the maximum HP for the entire RPM band. Ive said that twice, its how its done, wtf is wrong with you?

 

119 hp to the ground at 130mph. Happy? Notice that number means nothing. Its not how much HP the engine makes, or how much HP actually gets to the wheels. its the net work done by the car including friction, fluid and solid.

 

You obviously lack reading comprehension skills too. That's great that you fumbled your way through two semesters of high school level physics classes without learning basic terminology, but I'm looking for answers from people who are a bit more educated.

Do you even have calculations for how you came up with your number? If it's as simple as you make it sound, post your spreadsheet with the calculation columns, and your graphs of Torque vs RPM and HP vs RPM.

Maybe you should just stop posting and save yourself further embarrassment. You obviously don't understand the question that is being asked.

 

This thread shouldn't die...BUMP!

 

HP = 745.69987158227022 (Watt)

Watt = (kg x m^2) / s^3

kg = 2.20462262 pounds

m = 3.2808399 feet

HP = (745.69987158227022)(lbs)(ft^2) / (s^3)(2.20462262)(3.2808399^2)

HP = (31.4238746)(lbs)(ft^2) / (s^3)

Now, here are your problems:

1) you do not know precise enough mass of vehical, fluids, driver, dirt on car, etc.

2) For best accuracy, ft => 0. Makes accurate timing difficult lol.

3) you have to do a number of points to try and flesh out a graph

4) it does not account for various losses like air resistance, drivetrain loss, traction issues, etc

but you ought to be able to get somewhere near what a mustang dyno would read. I think. Only one way to test it, and that requires you to hit the dyno anyways lol.

 

actually, here may be a better way now that I think about it:

F = m x a

Power = (F x d) / t

P = (m x a x d) / t

P = m x a x v

Power = mass x acceleration x velocity

would be a good bit easier based on the data you have now that I think of it. I'll leave all the unit conversions to you though.

 

HP*(550)= Torque * 2Pi() * 1/60sec * rpm

 

That's what I've been sayin'....

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)

But none of these methods give us a good #?????????????????

I'm wasted right now!

Late,
Nick

 

My car goes fast

Problem solved

 

It's funny...these guys seem to be able to do it???

http://www.bahntech.com/products/Auto_Dyno/default.asp

h8bumps, let's write some software and sell it for buko $$$!

Late,
Nick

 

It requires you to know the same stuff I pointed out. Weight, drivetrain loss %, and coefficients of friction. Not real sure where you would find good #s unless you have run your Z on both an engine and mustang dyno, plus had time in a wind tunnel.

 

lawl, ur still trying to figure it out My value includes wind resistance and average friction . btw, you dont have nearly enough data points. My value is power at 6000 RPM.

 

Where's the B.S. flag?

You can get a good approximation of what you'd get on a static dyno, but then again the question becomes "which static dyno?" They all read differently, even on the same car on the same day with the same setup, so it's all an approximation anyway.

Besides, we're probably talking about RW numbers, so you don't need drivetrain loss %, and coefficient of friction is also a "red herring" -- especially since there is wheel slippage on any non-direct-connect dyno. An exact vehicle weight is important in the calculation, but being off by a few pounds (or even a few tens of pounds) isn't probably going to throw off the numbers THAT much.

 

^ +1 , almost. Since you know the change in speed over the RPM, drive train loss, and friction is already factored into the time. The only problems is that I cant do enough calculations without setting up a program in excel to do it for me. One would have to do every calculation and graph it, and find the max, just like the dyno does. Im doing the psuedo math that a dyno does to get that number.

 

If you will notice, I was responding to the post above where a device was linked. If you care to look at the device, it does infact ask for exactly what I stated. I made up nothing, only read and reported what others like yourself obvious were too busy to look into. Here is specifically where to look:

http://www.bahntech.com/products/Aut...er/default.asp

Please, no BS flag for myself, as I am simply reading and responding, not asserting anything without considering, like how "a few tens of pounds" will not make much of a difference ( 30 lbs in a 3000lb car would make about 1% difference in your power numbers, small to some I guess but still something to be considered).