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Originally Posted by GtoRX7
Yeah when tuning a turbo engine, I do not use the dyno wideband. The internal dampening is too slow for quick decisions if things get out of hand. AFR for a turbo rotary strictly depends on how much generated heat is entering the engine. For example, I see ALOT of people running a turbine housing that is 1 inch away from the intake manifold with no heat shield at all! Hmmmm blown engine anyone?? But typically a nice safe tune will be in the 11.1-11.2 range. In a controlled environment or on a very well insulated/ well cooled turbo rotary setup, 12.0- 12.5 can be done. But that tune is not safe in my opinion in the real world at the track.
Now with that said, do not get too hung up on a 13.3 afr number. Yes n/a two rotors seem to enjoy 12.8-13.4 in the testing I have done as well. But remember not each rotor is burning EXACTLY the same as the other. And we typically are using only one wideband. So if you ever get into n/a 3 rotors, trying to tune for 13.3 might actually hurt power. Simply the variance and heat difference from the front of the engine all the way to the rear can cause this. When I tune N/a piston engines like the Honda b16 and b18, they actually made the best power at 14.0 afr. So dont cling too hard on values, and always let the dyno do most of the talking.
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My hat is off to you, sir!
Very well written reply - I couldn't agree more that test data trumps theory anyday, rules of thumb will only get a baseline, the dyno is required for peak power.
I was told that rotaries liked 12:1 AFR for peak power when I decided to throw a Haltech ECU in my car, I tuned to 12:1 rather than following my experience on piston engines because I didn't expect it to port across. Instead, I found that I gave up 40 WHp by tuning to 12:1, relative to 13.3 (where I would have tuned it if left to my own devices).
I was also told that ignition timing should be 26 degrees, I found peak power (+20WHp at 38 degrees - which is a good baseline number for a <10:1 engine). Thus I found the piston engine knowledge that I had acquired has ported over very nicely to rotaries.
I completely agree that chamber swirl has great effects on fuel distribution and therefore desired AFR for peak power (hence the tumble head design on a DOHC 4-valve cylinder requiring a leaner AFR).
I was mostly curious for my own information, as I have little to no experience with gasoline-fuelled forced induction engines, but I have pretty good experience with normally aspirated gasoline engines. I work with turbocharged diesel and Natural gas engines every day, so I am always curious how the parallels carry across.
My experience has led me to conclude that a higher compression ratio tends to make better torque and require slightly leaner AFRs while accepting less timing advance. I am always trying to obtain information that can help me apply these trends to rotaries. I am relatively new to rotaries as compared to my piston engine experience.
Don't give out information that will hurt your livelihood, but you have earned the respect of one amature rotary builder with your above reply.