Choosing an Engine in the Waning Days of 100LL

[zemon]

I am building a Bede BD-4C and have been planning to put a Lycoming IO-360 in it. Reading Avgas Replacement: Drop-In Appears Unlikely in AvWeb got me wondering, though. Is a motor that truly seems to run best on 100LL the right choice these days? Would a carburated O-360 make more sense? Is it reasonable to get sufficient cooling air past the fuel injector lines to avoid vapor lock in an IO-360 running mogas?

I am very comfortable with the reliability and parts availability of the Lycoming engines. I don't feel any particular need to become an engine experimenter.

-- Art Z.

[Chad Jensen]

I think that article, and the briefing that was held came across as unnecessarily negative, but a replacement is coming no matter what sort of "other" items have to be considered. It will get solved, and we'll still be able to run fuel injected engines. We obviously can't move forward blindly, but I'm confident a solution will come to allow "fuelie's" to run on whatever is on the horizon. I did put a carb'd 360 on my RV-7 for reasons based on the fear of 100LL disappearing and an unknown alternative, but at this point, I am planning a fuel injected 320 for my Tailwind... We had a live video presentation at my Chapter last month from the folks at Swift Fuel...there is good stuff coming from them, and they have taken on the engine experimenter role for us when it comes to trying a new fuel on engines designed around 100LL.

[Dave Prizio]

I do not think that there is much chance that some sort of 100 octane avgas will not be available for the foreseeable future. The loss of such a fuel would pretty much destroy general aviation.

However, if such a loss is a concern, it is quite easy to build up an IO-360 engine that would run on premium auto gas, assuming you could deal with the ethanol problem somehow. Aero Sport Power, for example, has built many engines with reduced compression ratios for auto gas users. Going with a carburetor does not help much with regards to dealing with this issue. Any IO-360 with 8.5:1 compression ratio should be as capable of running on premium auto gas as a similar O-360 with the same compression ratio. You would however want to avoid the IO-360 engines with 8.7:1 compression, which would include all of the 200 hp IO-360s.

Dave Prizio

[zemon]

Thanks, Chad and Dave. Sometimes a little encouragement goes a long ways and this is one of those times.

-- Art Z.

[FlyingRon]

Actually Continental says they can run with just about any of the alternative fuels proposed and further, they believe that while you will see less performance with 94UL than with 100LL, due to being rather conservative with their engine ratings, you'll still get rated power out of most of their engines.

[dbvz]

Expensive way to go, but has anyone looked into using one of the racing octane boosters? Here is a mix chart for one of them. I have not looked into what is in this stuff, or if it works. Often they say they will increase the octane number by "UP TO' some number of points. Kind of sketchy. This one gives a specific mix amount for a specific result:

http://torcoracefuel.net/2-docs/acce...r-ratio-93.gif

[heddergott]

If you decide to go with an O-360 engine for your BD-4, I happen to have an almost new muffler for that engine (15 min. TT)
It is left over from a BD-4 that I sold without the engine. klaush@sti.net

[Mike]

Harleykitplane.comExplained with photosMike@harleykitplane.com

[jaysmiths]

I'm building BD4 N157JS myself and having thought about the same 100LL issues, I'm using a Continental 0-470 with a custom intake manifold (six more or less equal length runners, ala the air-boat crowd), central plenum at the rear of engine and carbureted with a Rochester 2v dirt track racing carburetor with Holley jets (adjustable) and a modified power valve that only richens the mixture under near WOT conditions with a leaning mechanism built into the plenum. The carb which uses off the shelf rebuild parts --alcohol resistant-- will be encased in an aluminum box open only for intake air from the front of cowl, fuel line and the necessary cables for throttle and leaning operation. The purpose of the box is to reduce temperature in the carb area to reduce any vapor lock issues there. The engine will use gravity and electric boost pumps for fuel, NO ENGINE MOUNTED PUMP as this is a source of heat that exacerbates vapor lock.

For now, I'll run 100LL and some mogas too from time to time but am building this airplane for use 20 or more years in the future and by then ethanol laced gas will probably be what is available at anything like a reasonable cost. If the octane available "out there" a few years isn't high enough, the magneto timing can be pulled back a little to create a detonation margin of safety--TCM says that this engine will run on 80 octane anyway.