Bernie

Compression ratio is 10.8. From Paul: "The V5/V5S engine can run of 92 octane without any problems. It can also run on 89 Octane with a small ignition timing adjustment." This all sounds totally reasonable to me, and I'll be running one on ethanol-free pump gas 92 if / when I get one after training. Seems like the best option for me, right now.

Well, I was writing to Bailey, and in the process did some research about common 4-stroke dirt bike engines, avgas, compression ratios, and octane ratings. To completely add to my confusion, I guess the octane ratings in the UK are higher than that in the states, and the 95-98 octane requirement is actually equivalent to 92 premium in the states (because the UK uses RON, and the US uses MON). It does appear that more informed posters on MX forums also suggest to not use avgas in modern four stroke dirt-bikes because it collects on the titanium valves. However, now that I've learned about the octane rating difference, all my concern about avgas is probably moot, and I bet I can safely run 92 octane (in the US) without additives... I'll still email Bailey about the compression ratio and followup here. Somewhat interestingly, in the process I learned that my WR450f (dirt bike) has a compression ratio of 12.3:1. It blows my mind that I've been able to get away with running it on 92 (and not higher), but it seems like that's what everybody does. I think it even had a sticker on the tank when I bought it.

Thanks! Seems like that could work. Just kind of a bummer that I can't refuel with typical ethanol free premium found more commonly in the states (at 90-93 octane) without running an additive, while avgas is at basically every airport, so very easy to find... Anybody know the compression ratio in the V5?

LOL, right, my point was more that to generate meaningful statistics, you have to have a decent sample size. I hear what you're saying about quality though. Regardless, I'm starting to think that maybe a single 4-stroke is the way to go if I'm looking for reliability until I've engineered something better for myself. I noticed that Bailey now recommends against using av-gas, and recommends 95-98 octane. Here in the states, that's race gas and isn't the easiest to find (or the cheapest)--while avgas is. I guess Bailey must have fitted the V5 with a slightly decked head to increase compression or something? Or do people run the V5 on 92 octane successfully? I guess the real question I should be asking is: what's the compression ratio of the engine? I don't see it listed and I was unable to find it when searching. Alternatively, do some people run av-gas with a detergent like seafoam?

on the topic of 4-strokes, I'd also be interested to know how they are effectively oiled without some sort of dry-sump and air-separator in acro situations... i was thinking that might be enough for me--just go with a bailey v5, but it seems the volumes on sales are low enough that I'm still not totally sure I'd feel comfortable... and i'm not immediately seeing a Japanese 4-stroke dirt-bike option that doesn't have the gearbox and clutch built in...

I'm new to the sport, and I assume the answer to this is going to be some combination of cost, complexity (two starters, two clutches, double the electrics, and fuel lines), and weight, but I'd like to see if there's anything else to consider, or if people have stories about failed attempts. The openppg project has 4 electric motors and seems to work well--seems the only limitation is the classic energy density of batteries vs. fuel problem. There's the British twin-motor electric PPG. Though it doesn't seem to have gained acceptance, it does seem that others have had the same idea. From reading and watching, it seems that _active_ pilots (of two-strokes) tend to get about 1 motor out per year or per 1-200 hours. Given that, it kinda puts me into territory where I'd be worried about flying long distances, especially over water, rocky areas, dense trees, etc.. It would be really cool to have somewhat better confidence about doing so--at least having the ability to limp out. Seems to me the ideal paramotor would have two vertically-opposed 75-100cc two-strokes. Has anybody tried anything like this? Why / why not?