I have an IO-550N with GAMI injectors and on my first GAMI lean test it appears that the spread  between the first and last EGT to peak is about 0.2 gal/hr.  In otherwords - pretty darn good.  My ram air setup gives about 1.5 inches increase in manifold pressure. I intend to operate LOP at "high" altitudes (high teens mostly) and would like a smooth running engine. 

 

Is it the consensus of opinion that using turbo injectors and pressurizing them creates a smoother running engine?  Has this been consistently demonstrated?

 

The reason that I ask is that people that I respect have come down on both sides of this issue.  Some say that pressurizing the injectors is crucial, others that it makes no difference. 

• At what altitudes and at what settings LOP (20 deg vs 100 deg) do you notice this effect?
• If you turn off the ram air (but still run LOP) does the engine run more smoothly?

Obviously, I can test these issues myself in the future (I am still in Phase 1), but am interested in others experience.

Doug,

 

Perhaps you should wait until you, the airplane and the engine are broken in.  With the lean test results you have reported, anything you do can only make the spread worse.  In other words, evening the air flow to the injectors when such was not the case may create some A/F ratio imbalance leading to roughness.

 

Your results imply that the cylinders are pretty much producing the same power, a useful condition for a smooth running engine.  If your primary desire is for smoothness at LOP and you think the engine can be run at low power LOP 'cause it has been tamed, go test 'er now. Let's see, 25 miles is about 125,000 feet, well above your ceiling and still within Phase 1 limitations for distance from the airport.

 

What about the pressure at the injector bleed hole?  Well, an awful lot of people have been operating without pressurizing the air - but those have been airplanes not using the benefit of ram air.  Continental engines, usually with filtered air taken from the same engine cooling plenum that is supplying air to the injectors, should never see the pressure imbalance.  Even with a ram air setup, Continental engines may still not exhibit any problem because the pressure difference is not enough. 

 

Forget the consensus - every experimental aircraft engine installation may be different and results may vary.  If you think you can improve on your setup by considering the concepts, go experiment and report back.  You have an interesting starting condition and the before/after comparison could be educational.

 

If I had your current setup, I wouldn't do a thing for now.  

 

Grayhawk, AKA Others