Thread: Avgas Dicussion
01-18-2010, 05:41 PM #1
I'd like to start a dicussion on Avgas and it use in High Compression Ski Engines.
I've read a couple of posts here on this topic stating that Avgas is not a good "High Octane" fuel to use but I have just been given this document as attached for Race fuel 100. This fuel is 100% confimed to be Avgas rebranded.
So I would like to get some more discussion going on using Avgas and its "KNOWN" results.
My first question would be what affect does lead have on the engine and exhaust. I know you can't run it if you have o2 Sensors but is there anything else to consider.
01-18-2010, 10:42 PM #2
You might check out this site: http://www.answers.com/topic/avgas
The particular mixtures in use today are the same as when they were first developed in the 1940s.....The high-octane ratings are achieved by the addition of tetra-ethyl lead (TEL), a highly toxic substance....
Avgas is currently available in several grades with differing maximum lead concentrations. Since TEL is a rather expensive (and polluting) additive, a minimum amount of it is typically used to bring it up to the required octane rating and actual concentrations are often lower than the maximum.
Here's another little tidbit I just picked up searching this topic:
Av Gas is designed for low RPM engines. A typical aircraft engine does not rev much beyond 2,200 RPM. Av Gas therefore has a very slow burn speed and is typically not well-suited to high RPM engines with their much higher exhaust and cylinder temperatures.
01-18-2010, 10:51 PM #3
I've read similar stuff posted on this site. But I was hoping to get some feed back from people that have actually used it and what effects they have found it to have as it seems strange that Shell would promote it as a race fuel if it was as bad as posts would lead you to believe or is it all and urban myth.
01-18-2010, 10:55 PM #4
- Join Date
- Oct 2006
- Cleveland OH
Lead in the gas means lead will be in the water in the form of exhaust.
01-18-2010, 11:01 PM #5
- Join Date
- Oct 2006
- Cleveland OH
01-19-2010, 12:51 AM #6
- Join Date
- Jul 2007
- near Toronto, Canada
The MON number in the supplied PDF is 102 for Shell Racing Fuel 100 Plus, a 'premium octane, high lead, petrol...'
MON is essentially the aviation lean octane rating for the fuel. US AVGAS is also rated using MON, as far as I understand.
The scanned PDF text mentions that the Shell fuel is useful for engines that require greater than 96 RON / 86 MON (or greater than 91 Average Knock Index) [sic]
That 91 AKI is the same as the US octane rating for pump gasoline.
The NZ Shell Racing Fuel 100 info quotes a typical 102 MON and RON around 106, for a combined AKI rating of about 104.
That would be about 12-13 full AKI points higher than the NZ Shell V-Power, which is rated at 95 RON octane. 95 RON would be roughly 91 octane AKI (US Pump gas equivalent).
I can see why the higher RON/MON octane ratings seem appealing. It will be interesting to see what folks who have run AVGAS 100LL report in terms of engine power differences versus real race gasoline.
Higher Octane numbers usually mean slower fuel burn during combustion, so just putting higher octane fuel into an engine should marginally reduce power, unless timing or compression is increased to compensate.
Technical Data Sheet for Shell V-Power 95 Octane (RON) (aka NZ Pump gasoline)
TDS for Australian Shell Racing Fuel 100
Note that the Oz version saysthe Research Octane Number of Shell Racing Fuel 100 is between 105 and 110
and then this notation
(RON is designed for normal petrols and the method is not strictly appropriate for Racing Fuel 100).
That implies that the Aussies can purchase genuine racing gasoline, not just relabeled AVGAS.
Is there a Shell gasoline refinery in New Zealand?
Is there any refinery in NZ that produces race gasoline?
I like this quote from The Australian 300zx Owners Association;
...Avgas is what its name implies, Aviation Gasoline!
Its designed to be used in very large displacement, low RPM engines at very high altitudes.
Flame front speeds are comparatively slow making it far easier to control combustion which is a difficult task as the capacities increase.
This slow flame front propagation characteristic works against a tuner trying to get the most out of a small displacement, high rpm engine run at close to seal level.
The engine usually requires large amounts of ignition to produce meaningful power...
...Avgas makes a wonderful fuel for the brain deads to use which will allow them to make monumental stuffups in basic tuning and still have the engine not detonate itself to death.
This is particularly so in 2 stroke race engines...
01-19-2010, 03:58 AM #7
Highest RON pump gas available in N.Z is 98 but its only at a few places, highest standard pump gas is 95.
There is no refinery in N.Z for race gas.
Again I would like to hear some coments from people that have actually used avgas in there HI Comp machines. There is a ton of comments bagging its use because its for aircraft engines but no one giving some feed back that has actually tried it and it seems odd that a fuel company would promote a product for such use if it didn't work correctally as oil companies tend to cover themselves quite well against law suits etc.
One fact I do know is that a high performance race car engine can be made to produce more power using avgas than pump fuel if it is tuned for it and the person that passed this info on has the dyno readings to back it up!!!
So I'm still thinking if an engine is detonating on pump gas and not on avgas it must be making more power, because if it was getting deto on pump gas because the timing or comp is to wild for the lower octane it would sugest advanced timing and high comp would mean more power ???
01-19-2010, 04:32 PM #8
Can you use 100LL AVGAS in your ski? Yes
Will it offer more resistance to detonation than straight pump gas? Yes
Does it offer any benefits over 110-112 leaded race fuel? None other than cost.
Is 110-112 leaded race fuel a better choice for a high compression 2 stroke? Yes, without a doubt.
Just because a fuel company relabels AVGAS for use in regular engines doesn't mean it's right. They are just capitalizing on the people who use it and don't necessarily know what and why they're buying.
Like I said in your other thread...the fuel is designed with lower specific gravity, more light end hydrocarbons, lower vapor pressure, and has a burn rate tailored for use with low rpm, long stroke engines. The exact opposite of what you want in a 7000+rpm 2 stroke. Have I used it in my 2 strokes? No, because I know better, and have race fuel available. I have seen others use it without issue, however
01-19-2010, 05:07 PM #9
I'm confused. Everything you have just said doesn't seem to have a down side. Ohh and this is my fisrt thread on this subject
01-19-2010, 05:28 PM #10
Until you start eating the fish in lakes with a lot of lead residual in them. Lead is like Mercury it is absorbed into the fatty tissues of all organisms that come into contact with them.
Little fish absorbs a little into its body as it grows. Bigger fish absorb a little and eat a lot of little fish (absorbing their lead/mercury load as well), keep going until you get to peak predators. (Tuna, Baracuda,Sharks, Swordfish LM Bass)
That is the reason the government limits (or tells us to) the consumption of the large peak predators.
This is why all heavy metals are being taken out of manufacturing, (lead free, ROHS, etc)
Peace, Love and Black & Blue Tuna for all
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