juneau10
New Member
Hey, folks. I've been researching the engine in an experimental I'm likely going to purchase soon. It's an angle-valve, 200hp IO-360. I've been very happy running 91 AKI non-ethanol in my 180hp O-360 Cherokee for over a decade and 1000 hours now and would like to do the same with the new plane. After scouring the interwebs ruthlessly, it's not obvious how much margin there is on that combination. At the very least, I've got these thoughts to see if folks will ruminate with:
Detonation:
- Lycoming's 1070S says 93 AKI is necessary for an 8.5:1 O-360 parallel-valve engine, whether FI or not. The Petersen STC, my experience, and everyone I've talked to about it agrees that 91 AKI is sufficient. In fact, Petersen himself has said that they did the detonation testing with 89 AKI fuel but it was cranked up to 91 for the STC for even more safety margin. On the angle-valve 8.7:1 IO-360, Lycoming does approve a B95/130 Russian avgas. Not much more octane, but a little. Makes sense that the slightly higher compression ratio, better-breathing valves would require a bit more. Lycoming does its detonation testing at 500F CHT and 12% lean AFR(!!!). My thought is that with any sane engine CHT (400-425F being the hottest you'd want to run for longevity), 93 should be perfectly safe and 91 is probably fine if you're careful. Any thoughts/experiences with this sort of setup?
Vapor Lock:
- Petersen also said in a post somewhere that Bendix's FI is very prone to vapor-locking. I've tested autofuel with the volatility tester and found it to have varying pressure throughout the year, often boiling easier than avgas. Thus the vapor-locking is another biggie I want to address. Two things I'm thinking about doing:
a) Putting a valve of some sort to recirculate fuel from the servo back to the main fuel tank. This will keep the fuel pumps cool with fresh fuel and be sized to allow for full-power fuel flow to the servo even if it's forgotten about for takeoff. This was Don's idea from precisionairmotive, and I think it's a great way to keep things cool on a hot day/quickturn takeoff.
b) Installing a purge valve on the FI spider. Not really a vapor-lock thing, but more of a hotstart thing. I know precisionairmotive sells a purge valve with their FI system, but if one already has a Bendix system the cutoff function isn't needed and it requires another cable in the cockpit to actuate. Is there any reason one couldn't put a "T" at the spider, route a return line back to the tank with a simple manual, pilot-accessible shutoff valve? Nothing fancy to install on the engine, one small hose, and a simple ballvalve (maybe a checkvalve inline)... simple, light, idiot-proof (won't run if it's left on)...
Anything anyone else can think of I'm missing with these?
Thanks,
-Cory
Detonation:
- Lycoming's 1070S says 93 AKI is necessary for an 8.5:1 O-360 parallel-valve engine, whether FI or not. The Petersen STC, my experience, and everyone I've talked to about it agrees that 91 AKI is sufficient. In fact, Petersen himself has said that they did the detonation testing with 89 AKI fuel but it was cranked up to 91 for the STC for even more safety margin. On the angle-valve 8.7:1 IO-360, Lycoming does approve a B95/130 Russian avgas. Not much more octane, but a little. Makes sense that the slightly higher compression ratio, better-breathing valves would require a bit more. Lycoming does its detonation testing at 500F CHT and 12% lean AFR(!!!). My thought is that with any sane engine CHT (400-425F being the hottest you'd want to run for longevity), 93 should be perfectly safe and 91 is probably fine if you're careful. Any thoughts/experiences with this sort of setup?
Vapor Lock:
- Petersen also said in a post somewhere that Bendix's FI is very prone to vapor-locking. I've tested autofuel with the volatility tester and found it to have varying pressure throughout the year, often boiling easier than avgas. Thus the vapor-locking is another biggie I want to address. Two things I'm thinking about doing:
a) Putting a valve of some sort to recirculate fuel from the servo back to the main fuel tank. This will keep the fuel pumps cool with fresh fuel and be sized to allow for full-power fuel flow to the servo even if it's forgotten about for takeoff. This was Don's idea from precisionairmotive, and I think it's a great way to keep things cool on a hot day/quickturn takeoff.
b) Installing a purge valve on the FI spider. Not really a vapor-lock thing, but more of a hotstart thing. I know precisionairmotive sells a purge valve with their FI system, but if one already has a Bendix system the cutoff function isn't needed and it requires another cable in the cockpit to actuate. Is there any reason one couldn't put a "T" at the spider, route a return line back to the tank with a simple manual, pilot-accessible shutoff valve? Nothing fancy to install on the engine, one small hose, and a simple ballvalve (maybe a checkvalve inline)... simple, light, idiot-proof (won't run if it's left on)...
Anything anyone else can think of I'm missing with these?
Thanks,
-Cory
