To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Engine run

 

I'd really like to know what others are seeing for MAP

at idle from 800 RPM to ~2000 RPM.

I can't seem to get below about 15inches Hg.

Would any of you guys who have flown or have smooth

running engines at idle please respond with what your

normal MAP vs RPMs are for the low end around idle.

I have a TWM DCO 48mm throttle body and a short Atkins

manifold.

Thanks,

Jim

 

Jim;

 

I assume your TWM TB also has the adjustable idle by-pass ports – ports that pass some air around the butterfly.  I think they are used for precise balancing of the vacuum at idle between the runners, maybe to compensate for slight differences in the sealing of the butterflys.  If these are open too far, or, of course if the idle speed is set up pretty high, you won’t see low MAP at idle.

 

For lack of better idea, I set mine all open about 2 turns.  I’m guessing that if the idle stop is set for 1000 or more on the rotary, the settings of these doesn’t matter, but they should all be the same.

 

I don’t recall exactly now, but I think during the dyno runs on my engine, we could get the MAP below about 13 – 14” – one reason why I am now surprised to see MAP readings on the EM2 of around 11, and only 13 at 2000 rpm.

 

Al