Rotary Tuning Questions

Hi Andre, hoping I can actually get your input on this one. I have a few questions as it pertains to rotary tuning

1.) If tuning without an oil metering pump and relying on premix. Is the premix ratio and the air/fuel ratio something that needs to be decided on based off each other? What I mean is, for example at a weaker oil/fuel ratio would you choose a different air/fuel ratio? I've now listened to all HPA material on tuning rotaries and I have not heard you touch on this. At the core, my question comes down to engine reliability and probable failure trying to run air/fuel targets you discussed without taking into consideration oil/fuel premix ratio.

2.) Building off #1, would you absolutely leave the decel fuel cut turned off if tuning a rotary on premix to keep lubrication? Is it possible to damage the engine in this way?

3.) Why do you recommend running less split (a potentially more dangerous situation) at high boost versus the opposite? The timing split map you've recommended starts at 15 degrees in idle and light vacuum all the way to 8/10 degrees under boost.

4.) When it comes to split angle in relation to your base ignition angle. Is it the same if one chooses to run 8 degrees of split with 8 degrees of base table timing and another who chooses to run 12 degrees of split with 12 degrees of base table timing? From the engines standpoint in terms of what it is being subjected to thermodynamically...are those two situations the same?

5.) Is it possible to damage seals on a rotary engine from being too conservative with the ignition timing ? Can retarded timing actually push the engine closer to the detonation limit due to higher EGT? Or is the only consideration on being too retarded, damage to the turbine and waste gate from excessive heat exposure?

6.) Can you touch on the preferred strategy for rev limiting a rotary engine? Fuel only? Ignition only? Both? I've heard people speak about each of these being not good for the engine, but as always, I trust your opinion above all.

Hoping to hear from you or anyone else versed in rotary tuning.

Chris

Hi Chris, please see answers below:

1. I would not adjust my afr target based on premix ratio. This could potentially get quite messy since just about every rotary engine builder has their own ideas on the ideal premix ratio. Remember that if you're still running the stock OMP then there is still oil being injected and some of this is going to be combusted.

2. Yes. If you are running premix and use decel fuel cut then for the period the engine is on over run there is going to be limited lubrication supplied to the seals.

3. My split targets have been derived from what mazda do with a stock split map, plus my own testing. The numbers I use are conservative but if you want to be more conservative then you could run a fixed 15 deg

4. No, the split vs leading advance doesn't work like this

5. You wouldn't be likely to cause detonation specifically due to retarded timing, and EGT is related to, but not the same as combustion temperature. The issue with very retarded ignition is the EGT will be through the roof, hence to combat that and keep everything alive you'll need to run very rich AFR which will in combination with the retarded timing, greatly reduce your power potential. Generally I find that once you move richer than about 0.74-0.75 the power will start to drop significantly so this is a balancing act.

6. Many ECUs offer a rotary specific limiter option which is designed to use a combination of fuel and ignition to rev limit in the softest way possible. If that's not an option I'd choose a soft cut fuel limiter personally.

Andre,

Thank you very much for the response, I greatly appreciate it!

Just one last thing, I know you say your split angle targets are conservative but some may argue against that especially with 8 in medium to high boost.

I looked at the practical tuning example and you ended up running 8 degrees of split with 8 degrees base table timing at 15psi on 98 RON.

What's your thoughts on using that same split/base on 95 RON? Too much?

Chris