The EPA found out alky is corrosive also. When gas stations started offering it in my area a few years back, all the gas pumps at the stations failed.

I laughed, and laughed, and laughed.

I believe these little engines break the octane rules, since I have never seen detonation damage like a hole in a piston, or the edge of the piston eaten away until the ring is exposed. All the 36mm bore Zen engines have pretty high compression stock, because as the bores got bigger from 32mm, the factory did not make the combustion chamber much larger, if larger at all. Here are some examples.

G230 about 13:1
G260 about 14:1
the new G290 is about 16:1

The air cooled CY29 (35mm bore with a 2mm crank. Squish cut for stroke clearance, but no combustion chamber mod)--17.5:1

I have seen some of my competition build 30.5cc by the same method as the CY29, and I measured over 19:1 with a .020" squish

Measuring method (trapped volume plus Cylinder Volume)/trapped volume.

I know all those engines have run with the worst pump gas, and I have never seen a engine fail because of detonation.

I believe there are 2 reasons for getting away with this.

1) the trapped volume is very small, about 2cc, and probably burns complete because of the small volume. I know you can get away with more compression for a 125cc engine, than you can with a 500cc engine, so there seems to be a trend there.

2) Detonation takes time as the piston nears TDC. Since we hit double the RPM of larger engines, the time near TDC is less.

I would say the bigger factor is the small trapped volume though.

I never ran colman---but I am sure somebody has with high CR like above, and not failed because of detonation. But I would not try running colman in a larger engine and think I would be 100% fine. It is probably the low trapped volume (volume above the piston at TDC is what I mean) that allows these engines to run colman fuel.

Doug @ ESP

So Coleman camp fuel with a 55 octane and 8oz. of oil per gallon>>>>> Runs great???

I have heard it's fine - I don't run Coleman because of high cost here - I can buy race fuel for same price here.--- Lots guys like it because no smell - if you carry boat inside vehicle or store in side house than may be advantage. Also with no ethanol it's easy on carb diaphragm

More info - www.rcuniverse.com/forum/speed...ml#post11775521

Just putting it out there. To take ethanol out of pump gas. Mix 1 oz water to 1 gallon gas. Shake well. Let it sit for a couple hours. The water will blend with the ethanol and settle at the bottom of your container. Pour of the pure fuel from the top.

Why don't you just remove the alcohol from the gas? It's a simple thing to do. Time consuming, but simple.

SEE? It's SIMPLE.

We've dyno tested a lot of fuels over the years. There was no question that VP's U-2 ran faster in Quickdraws. The SAW record set on 2004 of 109+ mph with it still stands. Tyler Garrard's Quickdraw powered Whiplash still runs it at big events. It easily wins while running well outside other boat's wakes. However, the engines need to be set up with different pipe lengths, higher compression, and different ignition timing for different fuels. We tested various fuels on a modified Zenoah where we only adjusted the mixture. There was very little difference in performance. See Gasoline in the October 2009 Propwash for the details.

Lohring Miller

Guys I have used elf bfk for years in my little engines its non oxygenated but its pure fuel (no additives) after 12 months of racing my engines when pulled down look exactly the same as they did brand new no carbon and all clean,I also use the elf wrf which is an oxygenated fuel it again has no benzene etc in it and its also a great fuel
These little engines are worth alot of money and i cant see the point of putting cheap inconsistant fuel through them if its good enough for F1 and moto gp its good enough for my toy boats
Andrew

Doug you are right on the compression ratio being geometric, however the TCR is what will be a significant factor in producing power.(trapped compression ratio is after the exhaust port is sealed by the ring on the up stroke and the combustion area is calculated),
Stock 230 is 8.9:1
Stock 260 is 9.6:1
Stock 290 is 9.8:1
QD is 12:1.
Different timings and squish can change those numbers and require more or less octane requirements as for modified Zen's can run up to 14:1 on pump gas with moderate timings and as soon as you use a better rod ratio or a different combustion chamber design over stock that will give more TDC area dwell time and better squish velocity and centralization of the mixtures then the requirements will change for octane and cooling, however if the engine is loaded differently heavy boat, over propped ect., more octane maybe required as well as the cooling requirement and In these two stroke engines there is always residual unburned gases and any fuel with an oxygenated content VP, Nitro, ect will yield more power and heat. There is noting about these engines that one can bolt on or pour in and go without making adjustments or corrections for the changes that were made.