Felix

I need to put a disclaimer up front: I'm not looking to start WW III on rennlist, just to understand a technical point.

There's a been a lot of comment about what some people feel are inaccurate chassis dyno numbers being posted. I've recently come across a dyno graph that was indicated as having been normalised to DIN 70020 which uses 20 deg C and 1013.25 mbar ambient pressure as the normal values. The actual ambient air pressure listed on this printout was about 5% lower. This, combined with the temperature correction factor, meant that the measured power was normalised upwards by just under 7%. Is it correct to use this formula on a turbocharged engine? I can see it applying to a normally aspirated engine but turbos are also described as altitude compensators so I'm wondering if the measured power should be compensated with a different formula? Or perhaps not compenstated at all for pressure?

Geoffrey

It is normal practice to use a correction to some standard on either an engine or chassis dyno. You want to "correct to standard" the air entering the engine, in this case, it is before the compressor side of the turbo. A compressor works on pressure ratio and air density will make a difference, therefore, atomospheric air pressure and air temperature are important since air density is 2.7 * abs pressure / temp.

Felix

I agree about the temp compensation. But is it "fair" to use the same altitude compensation formula when a turbocharger just keeps stuffing air into the cylinder (up to its max capability) until the correct relative boost pressure is reached? At low altitudes this potential correction factor is small but at perhaps 2000 feet the correction is no longer trivial.

JamesE

Its all about the density...

Red rooster

Felix,
The whole idea is so that comparisons , even on the same car -different days, are meaningful .

For example a comparison between results obtained on a hot , muggy ,low pressure summer day and a cold, brisk, high pressure winter day would lead you to believe that something dramatic had changed !!

DIN70020 is an industry standard in Europe and should appear on any proffesional test result.

All the best

Geoff

JasonAndreas

Geoff(s),
The motronic ECU (I guess unlike a lot of other manufacturers ECUs) retards timing based on intake air temperature so how much of reduction in performance would one expect to see from this? I haven't read DIN70020 but would this standard of atmospheric correction really account for this additional compensation/trim?

Felix

Do you feel it's equally applicable to a turbo engine as to a NA engine even at 2000 feet above sea level? 6000 feet above sea level?

935racer

For all engine performance figures to be meaningful they must be corrected to "standard temperatures and pressures". There is a lot more to it than just temperature and pressure but you get the point. It does not matter if the engine is turbocharged or not the performance will vary with different atmospheric conditions. It is therefore vital to be able to take the figures to a standard base line so that meaningful comparisons can be made.
I am suprised that you run you mention was corrected by +7% but so long as DIN 70020 was followed and the dyno was correctly calibrated the end result should be correct. (The temperature in the cell must have been very high to give the 7% correction factor). Remember, of course, that there is a lot of "engineering" between the engine and the dyno on a rolling road so the performance figures are unlikely to be as accurate as from an engine dyno.
Hope this helps.
Richard.

TB993tt

I think this is one of the reasons why many chassis dynos cannot give good results with these tt engines. Yes one has the correction factor to DIN (or whatever standard) for ambient temp and pressure, but this does not take into account the Motronic doing its own "correcting" with the timing and boost.
I have data for my engine which may be specific to its programming but still gives the general picture of the function of the Motronic:
up to 32.25 degC inlet temp as seen by the ECU, optimum full load timing is allowed (and optimum boost)
over 37.50 DegC inlet the full load timing is retarded by 1.5 degrees
over 43.50 DegC inlet the timing is retarded X degrees
over 52.50 DegC inlet the timing is retarded X degrees
over 70.50 DegC inlet the timing is retarded over 6 degrees (and by this level the boost is reduced by 8%)
So if your "wizard" is trying to program your ECU on the rolling road and the intake temp goes above 32.25 DegC your numbers are cocked up from the outset.

935racer

Toby, I have often wondered about this! When we map our engine we use the air temperature into the plenums. We always compensate our power runs back to 50 celcius into the plenums as this is the maximum we see when installed in the car. It is definately not to DIN 70020 but for us is a more realistic figure as it is what the engine will "do" in the car. (Remember, this is on an engine dyno).
The motronic ecu will "compensate" (back off in your example) for air inlet temperatures into the engine, ie at the plenum or the outlet from the intercooler, and this is for safety reasons, not power. These compensation tables will almost inevitably be left alone by aftermarket remapping people so the safeguards remain as is.
Of course, it is not just motronic that has these facilities, almost all performance based ecus will have the same ability.
ECU's will log all sorts of data relevant to the engine performance. Temperature is obviously one, so is exhaust gas temp, fuel pressure, boost, inputs from the knock detectors etc etc. Motronic is a good ecu and has integrated a lot of functions. However, some of these are not relevant to the performance aspects of the car, such as anti theft etc, and remapping the unit is not the easiest thing to do! (There was no reason for Bosch to make it so!). I use Motec, not neccessarily because it is "better" than motronic but it comes with software that makes mapping easier. An ecu is after all, only a number crunching computer looking at a 3 dimensional graph. So long as the interpolation algorithms are correct you will not get more power from one make than onother. The skill is inputing the correct numbers into the map.
Hope this helps.
Richard.

Geoffrey

It is important to keep your test scenarios reasonable in order to have repeatable consistent results. The correction will work well within a range where the ECU is not doing anything drastic to ignition timing due to IAT, cylinder head or engine compensations. Obviously, a cooler engine will make more power than a heat soaked engine and the correction factor is not designed to address this issue. The correction factor is to correct the output to a standard so if the engine is tested in Denver (1mi high) it will produce the same output as an engine tested in Florida assuming all other things equal. The fact that it is turbocharged is irrevelant.

Red rooster

Looks like we all agree !! DIN70020 is an air density calculation that compensates for atmospheric conditions. It is used for all types of dyno- chassis and engine.
The various versions of Motronic have their own safegaurds for installed conditions. Turbo applications pay particular regard to intake air temperature -density and reduce boost /timing to avoid motor damage. That cannot be easily compensated for as in most cases the control algorithm is non linear.

The answer is to run the motor under the best conditions that can be obtained and then apply DIN70020 !
For interest ,OE engine development is done on an engine dyno and then on a combination of chassis dyno and road test to correct any " installed " issues such as intercooler operation on a turbo.

As ever these days , emmission compliance is the overriding factor.

There are so many conflicting issues that neither an engine or chassis dyno can be called absolutely correct !!

All good stuff.

Geoff