Druff1

Back in the day when i raced motorcross we used to mix 50/50 VP fuel and pump gas, in our 2-sroke bikes. Does anyone use this method in their engines? I thought someone told me one time that your motor runs cooler on Turbo Blue?

Druff1

Nevermind i should of used the search first.

Tired Old Man

My Feedback: (1)

Generally, anything greater than pump premium is a waste of money.

khodges

My Feedback: (1)

Agreed. All octane does is raise the flashpoint of gasoline. In high compression engines , it helps prevent preignition from the heat of compression and hotspots within the cylinder. Not very many of our model airplane engines need more than 87 octane. One of our club guys swears by avgas, runs 100LL all the time. All I can say is it's his money.

pe reivers

Not so. The flash point (Pensky Martin Closed Cup) depends on volatility of the different fractions in the gas. This is not equivalent with octane rating in the fuel, which mostly depends on burn speed.
All European engines need premium gas of 91 PON (pump octane) (MVVS, Evilution, ZDZ, 3W etc)

khodges

My Feedback: (1)

Thanks for the corerection, Pe. I guess I was thinking of why higher octane reduces "spark knock" (pinging) in performance engines, and knew it had something to do with how the gasoline ignited and/or burned. My streetbike would hardly run on anything less than 91.
As far as the European-made engines requiring higher octane, I guess that equates to the more you pay for the engine, the more you have to pay for the gas to go in it. I should have remembered that, as I had a ZDZ.

Tired Old Man

My Feedback: (1)

Pe,

I agree, but in this country we don't have any control over fuel quality or purity (which is all over the scale) so unless you want to buy some extremely expensive racing fuel octane ratings are a good general guide. Over here you never know what the EPA additive of the week will be. Most of the U.S. made and Chinese engines have lower compression ratios than those from Europe. Here in the U.S. using "premium" gas with octane ratings above 90 seem to work out ok for the European engines and using "regular unleaded" with octane ratings of 87 and above work out well for the rest. When it gets hot outside, say above 100f, the lower compression engines benefit from the use of premium fuel where the European engines need closer to 100 octane (our measure) to prevent pre-ignition. Which is why I said "generally".

VPL racing fuels are where most would have to go here for better octane ratings and vapor pressures. Expensive without even looking at HazMat shipping!! Avgas has so much lead in it that the stuff is more trouble than it's worth.

At least on this side of the water vapor pressure and flash points go a bit beyond what the average modeler is ever going to care about.

rlmcnii

My Feedback: (3)

ZDZs do require premium gasoline and they are European. Rotos are European and apparently don't.

Does not a higher Octane Rating enable gasoline to resist detonation (the explosive, rather than orderly...along a flame front..., burning of a gasoline-air mixture in an engine) as opposed to pre-ignition (which is, as the name implies, the ignition of the fuel-air mixture previous to the intended, or proper, time.)?

I would not put 100 low-lead in anything that did not require that fuel. The lead residue left behind would be for more trouble than it is worth.

pe reivers

You are right about the detonation and preignition, which aretwo totally different things.
The ROTO also requires premium fuel. I am 100% sure about that, unless ROTO makes special engines for the US market.
In Europe, your crappy low octane stuff is not available, even if you want to get it.
We have as lowest Euro leadfree 95 octane, which is RON. (research octane) PON (pump octane) is typically four points lower, but in good quality fuel the difference is less.
ROTO, which followed the MVVS success line, also has it's compression ratio maxed out for best performance on the available fuel, which is 91 PON. IIRC, they also ask for premium fuel in their manual.

Kweasel

My Feedback: (29)

All things being equal, larger bore sizes will require higher octane. Not an issue with the common 26-60cc singles. Its not difficult to find the limits of pump gas in larger cylinders though.

rlmcnii

My Feedback: (3)

pr,
According to the RC Showcase website, they may be the U.S. importer/distributor (not certain) of Roto, the Roto engines run on U.S. regular gasoline. They may have been changed and the website is not current. I do not own a Roto, but do have three ZDZs.

My comment about detonation v. pre-ignition was made just to clear the air a bit. I was not, and am not, certain that the terminology had not been changed over the years. They are, as you say, two different things of different causes.

U.S. regular gasolines are not junk in their intended uses.

pe reivers

I did not use the word "junk", as it surely seems to work well in some engines.
I said crappy. This is because of the many reports of different quality levels US-wide I have read here, ranging from quick gunk formation to uncontrolled amounts/concoctions of oxygenisers which can have a negative influence on Walbro parts and bearing seals. It is to be understood in relationship to the European uniform standards. I see no negative reports on these fuels.