I've already searched and read the archives on this topic, and found some good information. The thread that sticks in my mind is one started by Gordon Monsen. This thread provided some good insight into what the overall trend of the ignition map should look like, with information from Rice Racing regarding the ability to further advance the timing when the motor falls off the torque peak. However, what I am interested in is how to arrive at these maximum timing values without damaging the motor. It is relatively easy to set the fuel map to virtually any air/fuel ratio one desires with use of a wide band lambda sensor, but optimizing ignition timing is difficult to do safely on the rotary. On a piston engine one has the luxury of hearing a ping and backing off timing, whereas with our engines you're likely to break an apex seal.

I'm not saying that I absolutely have to run at the absolute edge, but how do you even determine what is safe and how safe it is? Some information can be provided by monitoring EGT's (I have one in each primary tube, upstream of the turbo), but again, that doesn't provide any certainty into how close one is to the danger zone. Can anyone provide some insight?

 

This is hard, the ONLY way in is done by proffessionals, and in all honesty it must be done, via an engine dyno or some other accurate source.

You need to tune for MBT or KNOCK LIMIT at every point on your map to get a true "to the edge timing map"

The MBT or mean best torque is what you you will tune to in the ranges of 50kpa Absolute up to around 140kpa absolute engine pressure all the way from idle to redline. From there usually the knock limit tends to be the thing that stops you advancing the timing any more on CONVENTIONAL fuels.

This is how I do it, this is how racing engineers in charge of companies like Honda in the turbo days did it, it is the ONLY way to do it to get the maximum, and it varies for each idividual engine system and atmospheric effects as well.

For the MBT you simply keep on advancing the timing untill the more advance you give starts to reduce the amount of torque you measure on the dyno, and for the knock limit assuming the torque keeps rising with more spark advance you stop when you start to notice the first signs of knock.

To all of this then you add your saftey factor for fuel and changing factors to give you a margin of saftey for when the fuel gets to hot or when you get a bad batch etc. In many ways it is easier if you do not have these facilities to just follow what others have done, but make sure to get ALL the details from them in regards to fuel specifications, ambient conditions, engine parameters before placing your faith in what they tell you.

Hope this helps.

 

Thanks for the reply RICE RACING, that is pretty much what I had expected. I have near unlimited access to chassis dynos, but not an engine dyno without excessive expense. A chassis dyno certainly won't allow you to recognize the torque falloff that will begin to occur before pre-ignition.

So, it seems those of us in this position are pretty stuck. Looks like I'll have to beg or buy the best information that I can. Too bad it gets so expensive when we get it wrong.

 

Uh, why not?
I've done it on an H22A messing with cam gears and a Haltech...


-Ted

 

Do your cahssis dynos allow you to hold say 5000rpm and 10psi boost static eg for 10 seconds or greater?
Giving you time to dial in more or less ignition at this point.

You would need to do this to generate a map for points like this, bit like what you do on a engine dyno.