No Map/??? as Efficiency Point in M84?

[Martin]

Doing a Supercharged car with an M84.....im missing the MAP/BAP %


Will it be incorparated in the next release?

[Martin]

Hi Shane,
The MAP/User1 efficiency calculation method has not been included in the initial release of M84. This has something to do with the way the software was put together and was not intentional but including it would have caused a delay in making the M84 available. We are planning a software update in the very near future to include a nitrous function and some other changes and we will include appropriate alternative efficiency calculations at the same time.

Anything yet Ross?

[DarrenR]

Hi Shane,

Going back to your first post, you are correct in saying there is a difference in MAP only to MAP/... as efficiency point, but it is nowhere near as dramatic as you have made out.

Here is my 2c on the matter.

To use an example close to yours of WOT, but 100kPa BAP as it simplifies and corrects the math. Using MAP/BAP as efficiency so 100% efficiency and the engine is tuned requiring 100% in the table for the particular engine rpm. The IJPU is 10, so 10mS PW for the correct lambda.

Now here lets close the throttle to 70%, making 80kPa in the manifold and an efficiency of 80%, the engine now needs 90% in the fuel table (this is typical) for the correct lambda, and 80% MAP comp is 7.2mS PW.

If we then travel to were the BAP is 80kPa and go to WOT, so 80kPa/80kPa = 100% eff, the table value is 100% as before (same rpm, et, at, etc.), apply the 80% MAP comp to get 8mS PW. This does not necessarily give the correct lambda, it’s just what we get as the sites are tuned at 100kpa BAP.

We get a difference in the PW for the change in BAP, more fuel for the same efficiency point, but less backpressure in the exhaust so more fuel should be required. How much more is the question, that will vary engine to engine and with MAP/BAP the amount is not tunable.

Lets switch that to the MAP only method and use the same figures.
We get the same result at 100kPa BAP, 10mS PW for WOT and 7.2mS for 80kPa MAP.

Now go to 80kPa BAP so WOT is 80kPa MAP and it uses the 80kPa efficiency point of 90%, after applying MAP comp we still get 7.2mS of fuel, and there is the difference in the two methods, no compensation for exhaust pressure due to BAP change.

The question goes back to ‘how much does exhaust back pressure effect the efficiency of an engine???’ In some cases MAP/BAP will come out fairly right (probably the majority), in other cases MAP only will be much closer to the correct mixture at all BAPs But probably never 100%.
The areas that affect efficiency from exhaust back pressure are cam timing and duration, compression ratio, exhaust manifold design, turbo or NA, exhaust system, mufflers, etc. Many, many things that vary widely from engine to engine. MAP/EMAP will compensate a little better for a couple of these points so is slightly better.

I think a better way to tune is MAP only as efficiency, MAP comp just because it flattens the main table, and BAP as a compensation, increasing fuel a very small amount as BAP drops. At least the amount of extra fuel you add is then tuneable unlike with MAP/BAP. MAP/BAP with MAP and BAP comp is probably better again. But the best would have to be a 4D table with BAP (or EMAP) on the Z axis, wouldn’t it??

Cheers,

[TunedByShaneT]

The point I was trying to make was that you should be able to make the choice whether to tune with Map/?? or some other more desirable load input.

As for Map only I disagree with your conclusions.

when I tune the engine at sea level with 80 kpa in the intake manifold and 100 kpa in the exhaust I need to remove fuel from the fuel table to get to the correct lambda value when compared with the 100 kpa sites (100% efficiency at sea level). Then when I go up to altitude, so that I have a local pressure of 80 kpa, and go to WOT so that I have 80 kpa in the intake and 80 kpa in the exhaust (100% efficiency) I will be running from the 80 kpa load point on the table, a value smaller than what is needed to properly fuel the engine at 100% efficiency. If I was not interested in having the lambda stay the same at altitude I suppose this is would not be a problem.

As for backpressure it absolutely effects the engine's VE. More directly, the pressure from the intake to the exhaust or the pressure ratio is what I am really concerned about. Take a good running engine - even idling, and stick your foot over the exhaust pipe - restricting it a bit and watch what happens to the lambda. In this case the actual backpressure is not horribly relevant to me unless it is compared to the intake pressure or I plan to do a compensation table for backpressure (maybe that could be the 4th D)

As it pertains to using both Map comp and BAP comp together I believe you will find that you now have a situation which doubles the amount of compensation which is required.

In any case I am very pleased to see that this method has been added back to the M84 software. Now we can all continue to tune in the manner in which we so choose for the given project.

Thanks for your time.

[miguel st205]

When do you gonna update the softaware of the M84 that corrects those things and more??...

Grettings...

[RossB]

The new version of M84 ECU manager is available now. http://www.motec.com.au/software/latestreleases/.