Actually I think it has a great deal of relevance, think about it for a moment. If you were to change the roller load what happens to the force being measured by the pressure transducer?
Simple logic tells you that the more load placed on the rollers by the load cell device, the more force will be measured by the pressure transducer. This is true up until the load torque equals the maximum engine torque applied to the tires. At which point acceleration stops, and you can measure the maximum HP/TQ provided by the engine minus frictional losses. This type of measurement does not show rotational inertia energy being transferred to the drive train components.

In order for this type of dyno to accurately interpolate the pressure transducer values into actual wheel engine HP/TQ on acceleration testing, the system must know with great accuracy how much actual load is being supplied to the rollers at all times. Does that make sense? Can you now see how this system has a larger margin for error?
It is not nearly as simple as some would lead you to believe.

This is why the ramp rates and load factors programmed in by the operator are so important to accurate measurements. It has already been demonstrated on this forum, that by changing the ramp rates and load values you can get wildly different HP/TQ values from these systems.

So once again I have to insist that the pressure sensor accuracy is only one of several factors in determining the accuracy of this type of dyno. Do you still disagree?

You really lost me on this one, help me find the flaw in my logic, but here is what I think: The force on my backside is there because the car's acceleration increases at a much faster rate. The reason the car accelerates faster at this RPM point is because the engine torque making it to the wheels has also increased by a substantial amount. Do you know of a way to make a car accelerate at a faster rate without increasing the torque to the wheels? jet packs maybe?
The other fact is that all of these so called less accurate dynos show the torque peak to be right where my backside says it is, hmmm funny coincidence eh.

Yes, Yes, technically it is energy transfer not loss, but for the purposes of simply measuring acceleration engine power to the wheels, I think we can safely consider them as a loss.

I agree, that is why I have repeatedly asked for some one, any one, to perform some constant load measurements and compare them with an acceleration run, same car, same gear, same time/day. In fact I would like to see this test done for each gear if possible. This would help us understand drive train losses/transfers a little better. Perhaps the results of these tests might show something they do not want us to see? And yes I am goading them, if that is what it takes to get some real info, as opposed to the marketing BS they keep regurgitating.

Good, they started a thread, I responded and then never heard back from them.


Kind regards,

Eric

 

Shootout mode allows you to compare the results of more than one Dyno Dynamics dyno (with different operators/testing methods) to one and another. It's basically a equalizer. It automatically controls ramp-up rate, inertial factor, etc. This basically takes the dyno operator out of the equation. The only thing that the operator inputs is the kind of car being dynod (rwd, 2wd or awd, 4cyl, 6cyl, 8cyl, etc,) baro and temp which is displayed at the bottom of the page. You'll notice that using shootout mode, one can also plot S_HP which represents a flywheel hp estimate. Same with S_Torque.

Cheers,
shiv

 

???

 

There doesn't seem to be any dissagreement to the points I have made? As I have already stated several times, this dyno has some really nice features for tunning, trouble shooting, and packaging. But accurately measuring and comparing real world acceleration power is not one of it's strong points. There are just to many factors regarding the system and it's operation that could skew the numbers.
While no system is perfect, a true constant load inertia dyno seems to be far more accurate when trying to compare real world acceleration power, especially when comparing different cars and dynos.

I do not wish to waste any more of Shiv's time so don't feel that you have to actually respond, but something you mentioned in this SCC truck test was very interesting to me.

As I have already pointed out on an acceleration test with an active load dyno like yours, increasing the retarder load will obviously increase the torque measured by the pressure transducer (load cell). Obviously the actual torque to the wheel/tire is higher in a lower gear, so this is why the real world acceleration times for each gear are very different.
If you increase the retarder load so that the acceleration time in this low gear mode is equivilent to the higher gear (as you did hear), it stands to reason that your load cell would measure much higher HP/TQ (which it did), in the lower gear. IMO this had little or nothing to do with increased tire friction and more to do with improper measurment procedures.
This is probably why your 3rd gear EVO testing showed more HP than your 4th gear testing, which is just the opposite compared to a true constant load inertia dyno.



Do you honestly believe that you tire friction loss increased by 22KW? If so all I can say is get the marsh mellos because the tires are cooking. Use an infared temperature sensor and point it at the tire/roller during the run. It may not be 100% accurate but it will give you a ruff idea of the heat energy being expended. I think you will find that your not any where near this type of frictional heat loss.

I do hope peolpe are not taking any of this personal, I obviously have my own opinions. If there is credible data and or theories that prove otherwise, I am more than willing to openly admit I was wrong. Questioning, arguing, making mistakes is all part of the learning process, provided we keep an open mind.



Kind regards,

Eric

 

Eric,
The reason no one wants to keep arguing with you is because all your statements concerning the accuracy (or inaccuracy, as you call it) are your opinions based upon no firsthand experience. It's like arguing about a car you have never driven. It can't do that. It can't do this. Those (unlike you) who have used the dyno for tuning/testing and have seen it *repeatably* pick up things that go overlooked and completely unresolved by other measuring devices tell us all we really need to know. Go use the dyno, see how it really works and strike up this thread when you something new to say.

my 2c,
shiv

 

That just sounds like a lame excuse not address any of the valid points I have made.

I noticed your reported dyno numbers for the EVO have gone up since we initially started this debate. I find that highly amusing and confusing since it makes comparing new/old data impossible.
You are the one who openly started attacking every one else’s reported HP numbers, claiming that only your dyno is showing the true WHP to the road. I simply asked the question why? Why is your DD system more accurate when measuring acceleration/engine HP actually making it to the wheels?

I do not need to use this dyno to be able to question the results published from them on a car that I am quite familiar with. I have raised several valid points that have gone unanswered, I think it is very obvious who’s blowing smoke here.

Shiv writes:
I have repeatedly said:

 

Okay, Eric. Have a nice day.

Shiv

 

DAMN!!!!

 

I know, the fact that they will not properly address any of my common sense observations or provide additional information regarding these issues, tells me that I am much closer to the truth than they would care to admit. It's sad because there was a real opportunity to learn here, I guess if it makes there dyno look bad in the process, I could see why they would not want to continue.
I will at least run some constant load dyno tests with the Mustang AWD dyno, it should be interesting. I also have a good friend who owns and operates a Lingenfelter performance shop, they actually use engine and chassis dyno's for there work. There engines range from 400 to 800/900 crank HP, he is supposed to be getting me some examples of wildly different crank HP motors and how they read on a chassis dyno using similiar/same chassis components before and after mods/tunning. He did not have the actual data readily available, but from what he recalls the drive train losses were far from linear.

Hopefully these disscusions will at least quiet the USA DynoJet/inertia dyno trash talk from these individuals. If not I will be right there asking the same questions and making the same obvious observations.

Shiv you have a nice day also.

Kind regards,

Eric

 

ZzZzZz.. too much readinggggg