that makes abit more sense now mate, that's knocking on Veyron power/weight, must be a proper weapon

 

I think what he is saying is the DD ATMC2 correction was totally disabled.
I will try and get some graphs up here tomorrow to illustrate the difference that makes.

 

I believe that was the case, I will ask tomorrow when I see the guy who ran the dyno that evening. Thanks Stu.

 

don't forget the sae/din cuppa plot for me pllllleeeeeeeaaaassseeeee

 

Do you specifically want the plot from the brew mate?

 

if possible stu please mate if you could show the hottest temp sensor plot showing all the corrections din/sae and dyno dynamics own that would be great, after reading how much sae supposedly inflates the figures as temps rise id like to see some comparable data, your a star thanks stu

I guess the tea one was about 90d was it roughly ?

 

I don't think Dyno Dynamics use DIN at all anymore. Will take a look now as James is on lunch so I can access the computer remotely now.

 

I did the cup of tea (water actually) test on a dyno shoot out day a couple of years ago, my wifes Mini convertible went from 90hp to 115, doesn't sound a lot but as a percentage its huge.

 

It's a massive percentage.

Good topic this one

 

ok mate I have some data for din anyway for my car, its sae im mainly interested in as that's supposedly higher cr as the temps increase.

 

that's 28% martin is that difference from ambient upto cuppa ? if it stayed at 28% my old supra at 760 rwhp would of made 972 rwhp ! lol

 

Ok,
As most of you hopefully now know, a Rolling Road of any form simply measures power at the tyres (Not wheels, that's different)


That measurement is then corrected to a known standard that takes into account:

• Atmospheric pressure
• Ambient air temperature
• Humidity
• Intake air temperature

The problem here is that there are quite a few standards out there today, and the latest 2013 Dyno Dynamics Dynotech machines offer correction to the following standards.

• ATC
• ATMC1
• ATMC2
• SAEJ95

Or of course we can read it totally uncorrected and not really care about the powers accuracy against industry standards at all. (It will still read gains and losses, but the figures will be somewhat meaningless units with regards absolute accuracy to OEM level)

So, taking the run from the video where we placed the air probe into a cup of tea, we have the following data.

Atmospheric pressure = 1024mb
Ambient air temperature = 26.1 deg c
Humidity = 58.48%
Intake air temperature = 68 deg C. (The temperature of my cup of tea.)

The runs then produce the following power graphs depending on the correction standards chosen.

Uncorrected = 395.7bhp (No correction added - pure measured power)



Corrected to ATMC1 = 424.8bhp (Adds 29.1bhp)


Corrected to SAEJ95 = 426.9bhp (Adds 31.2bhp)


Corrected to ATMC2 = 429.4bhp (Adds 33.7bhp)


Corrected to ATC = 430.8bhp (Adds 35.1bhp)

 

i don't understand why you are so obsessed with getting the data from a run to show this. the correction formulae can just be applied to a measured (or fictional) power to give you the result. it's really not difficult

you can't say that a certain temperature difference will necessarily give a certain linear difference - it depens on the correction equation.

and again, it would not have made 972 - it would have been corrected to 972

 

I know its corrected ffs I don't need to keep spelling it out its fucking obvious, and how I read that I take it you think I am so diluded that I believe from a sensor being dropped in hot water I believe I will be actually making that extra power at the wheels, if that's the case then you sir can fuck right off !
I am not stupid I know its corrected readings, as for the corrections I have asked stu for the plots and he has posted them (thanks stu), if you don't like them don't read it, sometimes you are worse than a whining old woman on here !

 

thanks stu, the corrections are actually a lot closer than I was expecting tbh they are all in the same ballpark

according to foreigneRS I don't even have any right to be asking to see these plots ! fpmsl

 

I have seen several decent threads lately that have been ruined by "smarty pants" foreigneRS. It must make a man feel great to insult others - he is an engineer!!!! oohh, I am impressed! I am a physicist, should we compare mathematical skills?

 

so basically you need to be sure of 2 things when you go to a dyno!

1) Does the operator know what he / she is doing?

2) Do you trust them / believe them to be honest?

If you can answer both with a yes then then use the dyno! If you don't......

and for the record Stu setup my car last time and will do so next time! (when I finally get round to fitting the next set of mods!)

 

That's largely down to my cell mate - and that's where all this is open to a lot of interpretation from one dyno to another.
I bet if I opened my shutter door and did those same runs again the figures would all be totally different due to how hot the cell would get due to it not being closed up.

Some peoples dyno cells will even be below the outside atmospheric pressure due to having big extraction fans and woefully inadequate intake fans, while some will be above atmospheric pressure and correcting upwards due to large intake fans and little or no extraction so will be correcting down. The cell is FAR more important than the dyno itself.

 

you may know, but that's not how it reads to anybody that doesn't know so imo it's important to make the distinction to prevent any confusion. why get such a bag on about it?

i didn't say that at all. you're getting your handbag out for no reason

it's great that he has taken the time to do that. all that i'm saying is that it is not necessary when you could just put the figures in a spreadsheet, or any figures you like if you're interested in what diference they make to the corrections and then you can play around with data to your heart's content to see the different differences that a big or little temperature or pressure difference makes using each correction standard.

i don't know why you get so upset when i suggest that as an idea

1) why am i ruining this thread with my input?

2) i'd be interested to see what other threads you think i've 'ruined' and why

3) where have i insulted anyone?

4) as a physicist, doesn't it annoy you when people use the incorrect terminology for things that you understand and are in a position to inform about? isn't that part of the point of a discussion? there's no point all just agreeing with an incorrect statement just so the thread doesn't get 'ruined' by someone having an opinion

 

Come on guys lets not ruin the best thread on PF for years with bickering!

 

Hand bags! Leave it out. This is a good topic.
Had my rst ran at well lain years ago and the set up was nothing to what Kenny and stu have put to gather at msd.

 

Then there is the differences for when the straps are tight and when they're loose!

 

Is that just down to how hard the tyres grip the rollers though?

I don't suppose the rollers measure anything like pressure applied onto the roller, as every car is different?

 

No, far from it.
The more you strap it down the more is lost through frictional losses is the bearings and, more importantly, tyre deflection.

When you add weight you alter the tyres shape, and to deflect the sidewall and tread of a tyre takes power. As well as that, the tacho can end up out as well if you use the rollers as a tacho because under load the tyre is a different size than it is off load. Another error many dyno operators make as they don't set the tacho under load. It should really be done at peak torque with full load.

Tyre pressures cause a similar problem as the tyres heat up, the rolling circumference changes a little, as does the effective strapping tension.

 

Arrogance shines through Nick Fact is there are a lot of normal joes on here that are willing to learn and do not understand every form of terminology ! So long layman explanations are required and repeated to some extent to get to the point to correct wrong information not snipe comments or putting yourself on the mantle piece because your more educated than another user . Correct me if im wrong but tech learning threads like this have been a very big part of pf since the start ?


Now I have known you for what 10 years and when you were helping me years ago along with Stu and the others you never came across like this you were just glad to help

 

I don't need to add anything jay has said it all, cheers jay

I have no qualifications not even 1 gcse ! its not something I am proud of but I was always at work even through a lot of my school time, I may not have any qualifications but I run the maintenances/repairs side of a contracting company and a farm and the 30+ machines we have are all old, I am self taught and rebuild engines, gearboxs, final drives, turbos, pumps etc. im certainly willing to learn as ive learnt everything I know myself from research and workshop manuals before I took over all the technical work was sub contracted out whereas now I do most of it myself or my employees do it under instruction.


I will happily admit terminology isn't my strong point lol

but I know what I mean and I think most people do aswell.

 

If you put the before and after graphs on the same plot, there is only one AT/IT figure used, so you can hide a difference that way.

Another way of tricking the dyno dynamics that doesnt show up on the graph is to strap the car slightly looser so that in use it climbs onto the front roller only and hence removes the power losses driving the rear one apparently.

 

The whole truth and nothing but!

 

i'm sorry that i come across that way

i am still happy to help on any subject if i can and my suggestion about plotting the data from the correction formulae without needing to physically do it is a helpful suggestion in my opinion. if it is not helpful in any way, i'd like to understand why if it's just because somebody wouldn't know how, that is not my problem and if they said that then i would be happy to help in advising if i could.

look at the original thread about the rolling road correction - i have tried to be helpful on there by doing exactly what you have said in trying to explain it in laymans terms.

imo, not being explicit about what you are talking about just leads to further confusion, and has done on this very subject in both threads as you have people who have asking how a temperature sensor not on the car can affect the engines output.

if, as you say, people are willing to learn, then they should be happy to be corrected when they are wrong. if they aren't, how is that learning? it's just carrying on being wrong

anyway, it's nice to see chip making a rare appearance again he has a lot of experience and knowledge on the tech subjects and is an asset to the board in such areas.

 

Karl and myself need to pop the focus over to see whats happening power wise best thread i seen in ages anywhere top stuff
tim

 

Great thread

 

That is indeed true, it calculates the expected loss of rotating the rear roller. However, the correct way to run them varies, because a powerful car needs to climb the roller to get full traction as the vehicles weight starts to bear down on the roller centre line the more it climbs and with very high horsepower stuff you will never get traction without letting it climb so the only thing you can do is make sure that any tuning done the car climbs the same amount by correct installation and tension of the "Jesus straps"

 

now that would be very helpful, I have tried but looking at a formula is way over my head tbh and I don't know where to start

as an example say where at sea the base rate for correction with humidity and pressure so those variables are nul and void, id like to see the difference from din to sae corrections with the temp probe sitting at about 100c, that is exactly what id like to see but Id have no idea how to read the formula and work it out.
by base rate for humidity and pressure (if Ive worded that right) I just mean whatever the software uses as a 0 corrections start point if it could be done from there to make it easier.

the reason I am interested in that comparison is ive had dyno runs in sae and din cf and the article I read showed sae inflateing figures with high temps id just like to see it for myself through a plot or calculations.

if I took what you said the wrong way then I apologise, It just read to me like basically im stupid and I live in fairy land, like a dreamer with a 300 hp escort whos gonna smash rod at brunters

 

now we're getting on the same wavelength i can certainly do that and would love to it's the kind of geeky thing i like to do with my time

might not be tonight though

 

that would be excellent if you wouldn't mind

 

so could a rolling road just give a true non corrected figure of what the car actually makes on the day with whatever the air temp is.?

could the operater still fudge the result this way?

 

right, quick lash up of some data

the Correction Factor should be calculated according to SAE J1349 as:

Correction Factor = 1.180 [ ( 990/Pd) x (( Tc + 273)/(298)) ^ 0.5 ] - 0.18

where Pd is the atmospheric pressure that the measued power was taken at (in mbar) and Tc is the temperature at which the power was measured at in degrees Celcius (°C)

Now, that might look complicated, but if we break it down we can understand it easier. what it is actually saying is that the Correction Factor is just a relationship between the difference in pressure between standard (990mbar) and when power was measured (the 990/Pd bit), and the difference in temperature between standard (25degC) and when power was measured (the [Tc + 273 / 298] bit).

Let's put the numbers in for our pretend situation where we have done a power run at the standard conditions of 990mbar and 25°C but want to see what effect putting the dyno temperature probe used for compensation (that should be placed in the intake air stream) in a hot area under the bonnet that is at 100°C but at the same standard atmospheric pressure (so that we eliminate the effect of air pressure compensation and only look at temperature compensation):

Correction Factor = 1.180 [ ( 990/990) x (( 100 + 273)/(298)) ^ 0.5 ] - 0.18

the bit where the temperature goes has 273 added to it and is divided by 298 as it needs to be in absolute temperature as measured in Kelvin where 0°C = 273K (the 298 is the standard temperature of 25 + 273 = 298K)

by keeping the same atmospheric conditions, the 990/990 is just a multiplication of 1, so makes no difference

our equation can then be further simplified by doing the maths in stages so it could look like this next:

Correction Factor = 1.180 [ (1) x ((373)/298) ^ 0.5 ] - 0.18

then

Correction Factor = 1.180 [ ((373)/298) ^ 0.5 ] - 0.18

then

Correction Factor = 1.180 [ 1.25 ^ 0.5 ] - 0.18

the ^ symbol means 'to the power of'. if something is to the power of 2 it is squared, 3 is cubed etc, so to the power of 0.5 is the square root. it's just a way of writing it in simple text form where it's not convenient to use the square root symbol that you may be familiar with, the √

further simplification gives us

Correction Factor = 1.180 [ 1.11878 ] - 0.18 or

Correction Factor = 1.180 * 1.11878 - 0.18

and then

Correction Factor = 1.32 - 0.18

and finally

Correction Factor = 1.14

What this means is that if you do a power run at 25°C but have the temperature correction probe in an area that is 100°C, the measured power would get multiplied by 1.14 to give the corrected power.

in the case of the cossie that Stu shows an example of, where the measured power was at 26°C (which is close enough to the standard 25°C to make no difference, 1bhp), if a 100°C cheat were used, the measured power of 395bhp @ 7500rpm would give a corrected power of 395 * 1.14 = 450bhp

using the example that Stu has above, when the probe is at 68°C, the Correction Factor calculates out at 1.082 and 395 * 1.082 = 427bhp as his plot also shows. this proves my point that you don't need to do the actual run with the probe in the cup of tea to give you the data that you want

you can plug any temperature you like into the formula to give you the correction factor. i have done that for a range of temperatures between 0°C and 100°C and applied them to the data from the measured run above and plotted the corrected power figures that they would give. i'll post that up later when i figure out how to get the charts as a graphic (i'm using a new to me openoffice spreadsheet program, not the ms excel that i'm used to )

 

Trouble with removing temp correction would be if you ran on a day when its 5 degrees you would get a massive over reading as a result as you would be stopping the dyno from correcting the temp downwards.
The way to get an accurate figure is just to use it properly with the right temp for correction. Which I'm sure is what MSD do.

 

Both your explanations have been extremely long winded


But

Both your explanations have needed to be long winded so that they can be explained AND understood properly

Now I know what the correction figure maths is all about everything makes much more sense than it did before when I was nearly assuming the correction figure was something everyone knew about other than me

So thanks nick for your time and effort

 

Welcome back Nick. We have missed you.