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PP Rotary false lean questions

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A question for Andre based on your drag PP Rotary experience, we have a PP rotary dragster on methanol with a ProCharger on it, based on my understanding I would expect it to read a bit lean on the lambda sensor at lower-mid RPM with the amount of overlap and boost going into it (35-42PSI). However we are seeing 0.54 lambda and approx 1350F EGT's, clean plugs, about 7.3GPM @9,500 (calculated by FT550 ECU). Lambda ~0.82 at idle. Is it possible the air/fuel going out the exhaust at overlap is burning in the headers so not showing lean? And if that is the case then adding more injectors and optimising injector angle could show a leaner lambda particularly at lower RPM when moving towards optimal? There's obviously not a lot of info around on boosted PP rotary injector angle vs lambda.

I think if you dig back about 15 years on rx7club or nopistons you might find some stuff on injector phasing from the guys who were winding up drag motors.

I wouldn't say I'm an expert on PP turbo rotary tuning - I was involved with perhaps 2 engines that were PP in total. What i found is that you can pretty much ignore lambda under part throttle and low rpm conditions as the reading is too inconsistent with the port overlap. Once the engine is higher in the rpm and at full boost the lambda readings start to make sense. Fortunately for a drag engine you're really only worried about idle and then WOT so this is less of an issue compared to a road race or street engine.

Given your lambda at 0.54 and your EGT at 1350, I'd say yes, it's likely the combustion is continuing into the exhaust system. You absolutely can try experimenting with injection timing to see if that helps. In the projects I was involved with there was no real desire from the owners to spend more time on the dyno trying to fine tune these areas that the engine simply wasn't going to run in so I don't have much more feedback to offer sorry.

Hi Andre thanks for the insights. We're DYO bracket racing in the USA (no other classes we can run around here) so I plan to spend some dyno time shortly to make sure it's at least safe in the part throttle areas.

hi Michael, I had a dig around on those forums (and some others) and couldn't find much other than "here's the standard Mazda maps" and "here's what Haltech recommends" which is apparently different to their base maps anyway. Couldn't find anything PP specific. I'll do some testing on the dyno to see what happens.

It's relatively similar to tuning a wild cam piston engine in that like Andre said, at low airflow lambda may be a mess, but as airflow increases you reach a point where lambda is sane, and you can tune as usual. Happy tuning!

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