nigelspeedy
Well Known Member
The mechanical fuel injection crowd will likely be aware of GAMI injector nozzles. When I first started flying my GAMI spread was ~0.8 gph and LOP it ran very rough, as in it felt like it was going to tear itself off the mount rough. I went through about 6 iterations of injector nozzle changes, each time adjusting the most rich or lean injector. Rather than aiming for 0 gph GAMI spread I set them such that every cylinder achieves 25 LOP as close as possible. Not much different but it seemed to make more sense to tune the system for the operating point rather than peak where I never run it. I can see the benefit of using GAMI spread as an easy to understand and measure parameter though. Being a mechanical system I see a little variation in the GAMI spread depending on operating condition and one leaning event to the next but only in the order of 0.1 - 0.2 gph.
I found GAMI to be helpful and responsive, although I think I tried their patience as a customer searching for a perfect setup.
Just to put it in financial perspective, the kit for my 4 cylinder Lycoming was $600. In the first year replacement nozzles are free as you tune the system, you just return the original and unused ones.
Today at 9000' PA with an OAT of 19C (ISA + 22C) I got the following in my RV-8 with constant speed prop:
100F ROP, 10.6 gph, CHT's 375F, 185 KTAS, 17.5 nm/gal.
25 LOP, 7.7 gph, CHT's 345, 175 KTAS, 22.7 nm/gal.
Running LOP results in a 30% improvement in specific range (nm/gal) with CHT's 30F cooler, at the expense of a 5.5% speed reduction. The good thing is I now have the choice to run ROP or LOP as the situation and mood dictate.
Lets say you fly 100 hours per year, and 75 of those are in the cruise where you lean the engine and fuel is $5/gal. By running LOP you would save over $1000 per year. So for me it was worth it to have the option, save money on gas and learn a bit about how my engine operates on the way.
A couple of things I would do differently. First I used the standard Vans 3 lever throttle quadrant and I find the mixture lever to be a bit coarse. I would use a single lever for throttle and vernier knobs for prop and mixture if I did it again. Second I hacked and chopped the baffles in front of cylinder #1 & #2 early on as they were the hottest. Not realizing that mixture has a such a great effect on CHT's these ended up being the coolest cylinders once I had the fuel injection tuned, and subsequently I had to add back baffle that I had earlier removed to match the CHT's. So in future I would solve the fuel distribution problem before starting on the baffling adjustments (not to say that you should not do as good as job of sealing the baffles as you can).
Overall if you are have mechanical fuel injection I would say that balancing the nozzles is a worthwhile exercise from an operational flexibility and economic point of view.
Cheers
Nigel
I found GAMI to be helpful and responsive, although I think I tried their patience as a customer searching for a perfect setup.
Just to put it in financial perspective, the kit for my 4 cylinder Lycoming was $600. In the first year replacement nozzles are free as you tune the system, you just return the original and unused ones.
Today at 9000' PA with an OAT of 19C (ISA + 22C) I got the following in my RV-8 with constant speed prop:
100F ROP, 10.6 gph, CHT's 375F, 185 KTAS, 17.5 nm/gal.
25 LOP, 7.7 gph, CHT's 345, 175 KTAS, 22.7 nm/gal.
Running LOP results in a 30% improvement in specific range (nm/gal) with CHT's 30F cooler, at the expense of a 5.5% speed reduction. The good thing is I now have the choice to run ROP or LOP as the situation and mood dictate.
Lets say you fly 100 hours per year, and 75 of those are in the cruise where you lean the engine and fuel is $5/gal. By running LOP you would save over $1000 per year. So for me it was worth it to have the option, save money on gas and learn a bit about how my engine operates on the way.
A couple of things I would do differently. First I used the standard Vans 3 lever throttle quadrant and I find the mixture lever to be a bit coarse. I would use a single lever for throttle and vernier knobs for prop and mixture if I did it again. Second I hacked and chopped the baffles in front of cylinder #1 & #2 early on as they were the hottest. Not realizing that mixture has a such a great effect on CHT's these ended up being the coolest cylinders once I had the fuel injection tuned, and subsequently I had to add back baffle that I had earlier removed to match the CHT's. So in future I would solve the fuel distribution problem before starting on the baffling adjustments (not to say that you should not do as good as job of sealing the baffles as you can).
Overall if you are have mechanical fuel injection I would say that balancing the nozzles is a worthwhile exercise from an operational flexibility and economic point of view.
Cheers
Nigel