Nice work Mr Alex.T! You have my thanks :thumbup:

soi-duration-eoi-vs-mbt-ratio-t1485

Any chance you can expand your software to work out an MBT ratio too ?
Would be good to have a nose at how this looks across various models and makes.
See if there is common ground for base tuning SOI, and duration.

I don't quite understand your MBT..
You want to find this MBT thing that will help you build SOI map from scratch..
But you can't know when ignition takes place just by using fuel data (soi, duration, eoi .. )
Air is also important because fuel doesn't burn by itself. Air pressure and quantity will affect ignition timing.
Manufacturers will calibrate SOI based on fuel and air, you can't rebuild SOI just by using a made up map like MBT, because you're not taking in consideration air...

I'd really like to build something that calculates when ignition begins but it's engine specific and heavy math :(

Fuel cant burn any faster than it is introduced.
Either there is enough air for the chemical reaction or there is not.

fuel can't burn before it is introduced, we agree on that.
but fuel won't burn right in the moment when you introduce it.
sometimes will burn right away but usually it will start burning a few microseconds later...
how many microseconds later depends on pressure, because pressure generates heat.
if you have more air, pressure will be higher.. and that will have consequences.......
a few microseconds can mean a few crankshaft degrees...

So there will be a delay which will be proportional to duration then.....same result.
If the burn time is proportional to duration... it matters not.

Looking at the results you will see 35-40mg has a higher ratio than high mg or low mg.
Yet...this does not have the highest boost....highest boost is with maximum fuel.
Therefore...boost cannot have a major impact.

The attached table doesnt use TDC as the offset datum.
For this I used +8 ~ -8 degrees.
You will see the lines are spread out at the extremes but come together at 0 degrees.

Reality is match more complicate. If you not full understand all combustion aspects - not modify SOI and Rail Pressure maps. You can damage cylinder head or pistons. It is parameters overall heat of combustion cycle and degree TDC of max. cylinder temperature. Heat of combustion release to cylinder head, cylinder walls, piston and OG. All this balanced. When you modify SOI and Pressure without understanding all dependence you can shift this balance and one part will overheated. Other thing is place of max. cylinder pressure and speed of rise pressure. That other way damage engine parts.

Yes. But that does not mean there isnt a short hand way of getting similar quick and dirty results.
Do you think when you have soi setup on the dyno the tuner goes through all those calculations ?
:lol:

No. They will find best torque and then retard it.
Do you think they would get the same results @30c and 960mbar as they would @ 0c and 1060mbar ?
No they wouldnt....but does everyone go back for a retune for midwinter and midsummer ?
No they dont.

So my point is there is probably 1000s of people running around in tuned cars that were only setup properly fo one day in the whole year.
The rest of the year the timing will be out.

SO! Is near enough acceptable and what kind of tolerance is allowed ?
We already know SOI is retarded for NOX and Noise reduction....so far from ideal.

So what you want is a simple equation where SOI and Duration are both in crankshaft degrees:

Code: Select all

     SOI°
 ─────────── = MBT
  Duration°


Mathematically speaking, if you miss one of the members of the equation you can calculate it.

Code: Select all

      ?
 ─────────── = MBT             ? = MBT x Duration°
  Duration°


When I have more time maybe I'll add it to the program.

Anyway I don't think it's wise to apply MBT from one car to another.. but it's your choice..

Relic wrote:So my point is there is probably 1000s of people running around in tuned cars that were only setup properly fo one day in the whole year.
The rest of the year the timing will be out.

This is why the ECU has dozens of correction maps ;)

The basic formula is rght yes... :thumbup:

No... it would be a bad idea to apply the same MBT ratio to every car.
The civic looks about 1:1 @ 5000rpm (although 1.2:1 is average....1:1 would be safely retarded....High IQ is close anyway due to SOI limits)
The 530d only looks about 0.6:1.

So there is no way you could apply the same MBT to different engines (possibly IQ dependant too).
I would suggest every engine type would have its own signature MBT.
But it would be nice to see if the MBT ratio does scale in proportion to rpm for all cars.
Tis just an idea anyway to try and make things simpler.

You can start from rail pressure + MBT ratio or duration + MBT ratio.