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I posted a reply in the maintenance section the other day my experiences playing around with LOP and ROP using my JPI to monitor fuel flow, EGT, CHT. However, I didn't take into account that I have a Surefly EIS on the left mag so I went back out to retest.
PA32-300 Lycoming IO540-K1G5
JPI EDM830 monitor.
Original numbers:
5500-6500ft.
Best Power- (roughly 100-150ROP)
75%- 18gph
65%- 16.1gph
55%- 14.2gph
Best Economy (stoichiometric/peak EGT)
75%- 16gph
65%- 13.8gph
55%- 11.9gph
However what I didn't take into account is that during this original test, MAP tended to be around 24-25. Surefly doesn't start retarding the spark until 24.5" and gradually changes the advancement up to 38deg (I think, baseline TDC is 20deg on the IO540-K series). Therefore the surefly really hadn't done much to the spark timing and my best power numbers correlated exactly with the Lycoming and Piper manual for expected fuel burn based on best economy vs best power settings.
When I went back out to recheck- I started trying to set 55% power with a lower MAP/RPM combination (around 20-21") at a lower altitude. The EGT peaks wouldn't match up with what I was getting at a higher MAP setting so I re-did the LOP and ROP mixture analysis. I found that at 55% with 21" MAP, LOP is about 10.9 gph. So it looks like the advanced timing on the Surefly achieves about 1gph fuel savings.
As for CHT with Surefly- I have noticed increased CHTs since adding this. A prior analysis from a Kitplane article ( https://www.danhorton.net/Misc/Nigel Speedy - Ignition Advance .pdf) showed when the mixture was 100° F ROP, the average CHT increase was 2.5° F per degree of ignition advance. When the mixture was 25° F LOP, the average CHT increase was slightly less at 1.6° F per degree of ignition advance. That fits perfectly with what I am seeing. I see about a 15-30deg increase in my CHT across the board.
Now as to the question we have discussed in other threads- Lycoming certifies their engines to be detonation free within any mixture/MAP setting that can be found in the power tables. Whether the Surefly timing advance curves provide the same margin is unclear. Presumably the FAA was satisfied with their research or they wouldn't have approved the variable timing for the IO540.
Going LOP (slower flame front) with fixed timing pushes the point of peak pressure further after TDC. The result is lower CHT and a slight power loss. For LOP with ignition advance, the advance compensates for the slower combustion rate of the lean mixture, returning peak pressure to a point closer to TDC. (see this thread from an RV forum- https://vansairforce.net/community/archive/index.php/t-169923.html). The increased CHT during ROP climb with advanced timing as become synonymous with electronic ignition. However, this is more of a side-effect of the advanced timing map. In the experimental world, you could have two maps- one for LOP cruise and one for ROP climb. However, Surefly had to choose and chose one that is biased towards LOP cruise, and suboptimal for ROP operations.
PA32-300 Lycoming IO540-K1G5
JPI EDM830 monitor.
Original numbers:
5500-6500ft.
Best Power- (roughly 100-150ROP)
75%- 18gph
65%- 16.1gph
55%- 14.2gph
Best Economy (stoichiometric/peak EGT)
75%- 16gph
65%- 13.8gph
55%- 11.9gph
However what I didn't take into account is that during this original test, MAP tended to be around 24-25. Surefly doesn't start retarding the spark until 24.5" and gradually changes the advancement up to 38deg (I think, baseline TDC is 20deg on the IO540-K series). Therefore the surefly really hadn't done much to the spark timing and my best power numbers correlated exactly with the Lycoming and Piper manual for expected fuel burn based on best economy vs best power settings.
When I went back out to recheck- I started trying to set 55% power with a lower MAP/RPM combination (around 20-21") at a lower altitude. The EGT peaks wouldn't match up with what I was getting at a higher MAP setting so I re-did the LOP and ROP mixture analysis. I found that at 55% with 21" MAP, LOP is about 10.9 gph. So it looks like the advanced timing on the Surefly achieves about 1gph fuel savings.
As for CHT with Surefly- I have noticed increased CHTs since adding this. A prior analysis from a Kitplane article ( https://www.danhorton.net/Misc/Nigel Speedy - Ignition Advance .pdf) showed when the mixture was 100° F ROP, the average CHT increase was 2.5° F per degree of ignition advance. When the mixture was 25° F LOP, the average CHT increase was slightly less at 1.6° F per degree of ignition advance. That fits perfectly with what I am seeing. I see about a 15-30deg increase in my CHT across the board.
Now as to the question we have discussed in other threads- Lycoming certifies their engines to be detonation free within any mixture/MAP setting that can be found in the power tables. Whether the Surefly timing advance curves provide the same margin is unclear. Presumably the FAA was satisfied with their research or they wouldn't have approved the variable timing for the IO540.
Going LOP (slower flame front) with fixed timing pushes the point of peak pressure further after TDC. The result is lower CHT and a slight power loss. For LOP with ignition advance, the advance compensates for the slower combustion rate of the lean mixture, returning peak pressure to a point closer to TDC. (see this thread from an RV forum- https://vansairforce.net/community/archive/index.php/t-169923.html). The increased CHT during ROP climb with advanced timing as become synonymous with electronic ignition. However, this is more of a side-effect of the advanced timing map. In the experimental world, you could have two maps- one for LOP cruise and one for ROP climb. However, Surefly had to choose and chose one that is biased towards LOP cruise, and suboptimal for ROP operations.
