- Joined
- May 6, 2012
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I had a governor failure and major prop overspeed on my Rocket last year. Well, the mess is nearing resolution and a significant milestone was reached yesterday when the rebuilt engine ran across Ly-Con’s dyno. Since this engine has a fully programmable SDS EFI system, this allowed me the rare opportunity to validate “rich mixture” ignition timing insensitivity on an instrumented dyno. This experiment is a continuation of the flight testing I did in Death Valley a few years ago looking for any “peak” ignition timing point at 100% power. In that experiment, I did a 10 degree sweep from 20 to 30 degrees looking for any gains in speed. I was unable to discern any advantage based upon the IAS – it remained essentially flat. I opined that the airplane was hard against the drag wall and simply did not have the resolution to measure slight changes in power. It was admittedly a crude measurement.
Fast forward to yesterday when I once again did a 10 degree sweep, but this time I wanted to see how far of a retard from peak timing I could go before I took a big hit on power. Since I plan to run auto fuel in this thing, I want to retard my timing as a measure of detonation protection, but need to know where the “sweet spot” is. The results validate much of my in flight testing to date, but now I have hard numbers.
Disclaimer: I’m not going to defend the peak numbers shown here. This is Ly-Con’s data and I'm taking it at face value. What I’m more interested in is the percentage of power change with retarded timing. This data should translate well across the PV 320/360/540 fleet.
For general info, this is an otherwise stock 8.5 cr IO-540-D4A5 with the following modifications:
SDS EFI with 80mm throttle body
Ly-Con CNC ported heads
Piston oil cooling jets
The data as provided by Ly-Con:
Timing TQ HP
25° 620 320
20° 618 317
19° 615 316
17° 610 313
16° 606 310
15° 600 305
In this case, the peak power timing matches Lycoming's data plate value of 25 degrees. What’s interesting is the fact that I can pull a whopping 6 degrees out of the timing with almost no loss of power. So this tells me that I can program a huge retard into my takeoff curve and gain substantial detonation margin for no performance penalty.
So, for you guys running all the knobs forward, don't worry too much about timing.
Fast forward to yesterday when I once again did a 10 degree sweep, but this time I wanted to see how far of a retard from peak timing I could go before I took a big hit on power. Since I plan to run auto fuel in this thing, I want to retard my timing as a measure of detonation protection, but need to know where the “sweet spot” is. The results validate much of my in flight testing to date, but now I have hard numbers.
Disclaimer: I’m not going to defend the peak numbers shown here. This is Ly-Con’s data and I'm taking it at face value. What I’m more interested in is the percentage of power change with retarded timing. This data should translate well across the PV 320/360/540 fleet.
For general info, this is an otherwise stock 8.5 cr IO-540-D4A5 with the following modifications:
SDS EFI with 80mm throttle body
Ly-Con CNC ported heads
Piston oil cooling jets
The data as provided by Ly-Con:
Timing TQ HP
25° 620 320
20° 618 317
19° 615 316
17° 610 313
16° 606 310
15° 600 305
In this case, the peak power timing matches Lycoming's data plate value of 25 degrees. What’s interesting is the fact that I can pull a whopping 6 degrees out of the timing with almost no loss of power. So this tells me that I can program a huge retard into my takeoff curve and gain substantial detonation margin for no performance penalty.
So, for you guys running all the knobs forward, don't worry too much about timing.
