You should reread your post. You say "dyno is the most consistent way to measure power" and also say "of course variables are constantly changing". If that is true, then how can dyno runs be consistant?


You simply cannot argue that testing modifications on a track is a better way to judge performance because on top of all the same variables to which the dyno test is subjected, you are also adding human error.


Yeah, there is no risk of human error running a dyno. I don't believe that you would accept a dyno which showed more power while your car performed worse on the track.


Variables that effect dyno results: (not in any particular order)

- Air temperature, pressure and moisture
- Transmission and axle gear oil temperature
- Oil temperature
- Oil viscosity
- Crankcase oil volume
- Coolant temperature
- Fuel temperature (Fuel specific gravity changes)
- Tire size/pressure
- Wheel size/weight
- Force used to strap car to dyno
- Placement of fans
- Transmission gear used for pull (one guy made a chart from a pull in 3rd gear and then made a chart with a 4th gear pull. Customer was ecstatic with the increase in power his car had)
- Accidental or deliberate manipulation of the correction factor (always demand raw data)
- Vehicle weight
- Angle of tires on rollers
- Was the computer reset for the after mod runs?
- Intake temperature
- And many, many more…………………….

 

There is no debate here, to debate anything assumes subject matter expertise presence at both arguing parties.

Back engine pressure is controlled largely and it can be said solely by intake diameter of intake headers manifold and all subsequent flow obstructions of ideal free flow exhaust have to be compensated and worked around so essentially 'tuning the computer' is what happens there, speaking in your terms. In my terms, you unbalance previously balanced system with any bolt-on mods and then it requires to be re-tuned. Dyno machine is so far single known mechanism to do such tuning process possible as you have control more than a dozen parameters in real time under load.

Taking unbalanced untuned engine to 'track run' will simply destroy it.

As you denounce any tuning effort as pointless and have no understanding of dyno charts purpose in depicting internal engine parameters and processes, I do not see what can I do here and what to speak with you about any longer. Hope I made myself clear enough here.

 

Any available variables can be controlled to some degree if there is any intention of doing so. arbitrarily denounce any measurement just by the fact of theoretical discrepancy in some variables would destroy pretty much whole proving ground in modern theoretical physics. In reality there is always specific range in which certain parameters may and will be considered acceptable for any particular experimental results. It is more important to be able to enumerate and analyze influence from any available known parameters and correctly estimate possible factors from unknown parameters. As in any other life scenario it is impossible to know everything up front but it is not a reason to declare that any experiment is a fault by definition.

 

And the flow of water from your garden hose is solely controlled by the valve. Putting your finger over the end of the hose does not effect the flow or volume, nor does the size of the hose have any effect on how fast the water flows.

Putting your finger over the end of the hose increases torque and using a larger hose reduces torgue.


I can't believe all the things i learned on this thread today. I am so glad I am an open minded person.

 

To some degree, yes. To 100% certainty, no.

Throw into the equation the different Dyno equipment manufacturers, and the differences that each machine has, and the wear on a dyno...these can also not be controlled to a 100% accuracy. Also go look for the number of different drive train loss calculations that dyno people will tell you to use to calculate the crack vs wheel power (I have seen people claim 10-20% as the correct calculation).

 

So if you agree with the variabkle I listed, how can you trust a dyno chart unless these variables are monitored and controlled? Do you know the effect of strapping your car to the dyno using 30 foot pounds of force and using 80 ft pounds or the effect of runing your car with a 1% angle on the rollers?

 

I think YOU should reread my post. If you do, you'll find that I said dyno's are "the most consistent" way to measure power. I never said that they were perfect (in fact I acknowledged their limitations), but we live in an imperfect world. The point I was trying to make is that testing a car at the track is in fact far less consistent because you add a variable far greater than any of those you listed (almost all of which also apply to testing a car at the track, along with amt. of fuel in the tank which you can add) - human error! I know you said there is human error in the dyno - there's no disputing that human error, by its very nature, is present in anything where humans are involved in any capacity, but you cannot argue that there is less skill required to press the gas pedal to the floor then there is the shift, turn, brake, etc.

 

That article is a great find Ed.....wonder how true it is!
Here is the part I found most interesting.....

"There's no really accurate way to get engine horsepower from a chassis dyno," says Matt Harwood, marketing coordinator for Mustang Dynamometer, a major supplier of chassis dynos in Twinsburg, Ohio. Some tuners use the so-called 15/20 rule, which assumes a 15-percent driveline loss for manual transmissions and 20 percent for automatics. But, says Harwood, "I've seen losses as high as 35 percent." So unless it's printed in the brochure or was measured on a true engine dyno or by a tuner with tons of experience with your particular brand of car, any flywheel horsepower number quoted by a hot rodder under the shade tree is most likely just a calculated guess.

More important, did your car run on the dyno as it would on the street? If it's the latest model, chances are good it may not have, says BMW tuning wizard Steve Dinan. An afternoon spent at his Bavarian speed emporium in Morgan Hill, California, convinced us that cars are gradually becoming too computerized for the simple dyno test.

Dinan's cars are wired with a battery of sensors that report when the airflow over the bumper is too little, when the inlet air is too hot, and when the water temperatures in the block and radiator are too close together (most turbocharged and supercharged cars also "know" when their intercoolers aren't cooling enough). The computer reacts by backing off the spark and turning up the richness—and as a result, turning down the power—to prevent catastrophic engine meltdowns.

To prove his point, Dinan bolts to his Dynopack one of his 2003 Dinan M5s, heavily tweaked to make a claimed 470 horsepower at the crank (he expects about 415 at the wheels). With the hood closed and no external fan blowing air into the radiator, the car wheezes out just 334 horsepower at the wheels. An LCD data logger on the dashboard reveals the air-fuel ratio from the engine computer. Approaching redline, the BMW's computer richens the mixture all the way to 9.5:1 as the underhood temperatures soar.

And also this.......

"Basically, what horsepower would you like? I can give you anything from 330 to 420 with the same car," Dinan says. "Blowing air with a fan isn't the same as creating a bow-pressure effect over the whole front of the car. BMW can simulate that because it has billions to spend on wind tunnels. We don't, but we can come close by spending $250,000 to $300,000 on a climate-controlled room."


Stacy

 

you are obviously changing the point here, what I was saying initially was exact opposite - that all those dyno charts will have reason for your personal tuning efforts only. Original question was what to do in real life situation, without going into abstract discussion of mechanical engineering and experimental practices. And again, point was quite simple - use same dyno shop, same operator, and know what you are going to do. then you`ll have some chances to have relatively useful data to work with so you would know what areas of your system does require to be worked on. Consequent spinning of this simple claim I treat just like a pointless BS, to be frank.

 

Exactly. That is why no one here is concerned about true and ACCURATE _ENGINE_ power. It is not the point and never was. All we measure and work with is effective torque/power at wheels.

What you have to work with in real life, again, are timing fluctuations, irregularities in air/fuel supply, possible knocking, and many other simple enough things you can see ONLY under load while looking at all those charts.
Then based on this data you can try to figure out what is it to be altered to remedy that.

Point is not to 'measure' and compare to others, point here is to TUNE your engine properly after you change it.

 

Right. But you forgot in your fine example one single detail - connect your thin garden hose to fire hydrant first, then try to put you finger at its end.
then start speculating how does your finger control internal pressure inside of the fire hydrant.

That would be bit more accurate scenario.

 

You will minimize a few of the variables but not enough to get the accurate results, there are too many variables to control. And the net results would be as you stated pointless BS...to be frank of course!

 

Now you're talking about variable forced induction which changes everything. If you want your freer flowing exhaust to actually give you power, you need to put some pressure behind the intake. Here is a good product that you might benefit from:

http://www.amazon.com/Mimio-Electric.../dp/B000J5SPHQ

 

LMAO!

 

Sure, why not. Any net results are valid only within that particular dyno anyway. you still have you pre- and post- curves and will see relative overall difference between those curves. And if anybody does not seem to believe that 2+2=4 it does not change overall base rules of arithmetic.

That will do it, I have some work to do.