tkwalker |
10-16-2015 10:12 AM |
Octane and Ethanol <'TK><
This is a reprint from FishingTN Archives .
Okay folks there is a lot of misconception about this subject ... I'll bet less than one out of a hundred people actually know what octane is ... Here is the scientific explanation ...
"One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1.
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. (Dieseling) Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
The compression ratio of your engine determines the octane rating of the gas you must use in the motor. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more."
<'TK>< ..Okay Bottom line ... what this means is this is short of a diesel .. A diesel does not need spark plugs to fire ... They fire from High compression ... close to a 16:1 Compression ratio or more ... The clearance between the piston and Head is almost less than the thickness of a cigarette paper (compression and heat)... Which it takes a lot for a #2 Diesel fuel that has a very low heat coefficient ... (example every like an idiot throw gasoline on an open fire) .. Instant explosion and withdrawal of Oxygen ... Now you can throw diesel fuel on an open fire and it will accelerate but very controllable ... That is heat coefficient ... Now step up to Kerosene it has a higher coefficient ... More perky and right on up to Gas ...
So unless you have a high compression Racing engine you do not need to use High octane fuel ... Especially if the owners manual calls for 87 octane that is for a reason ... Most modern motors are fuel injected (large bore, High HP ) even the smaller Carb motors do to EPA are all designed for 87 Octane ... Even the 60 year old 3+ HP High compression race motors we build ..the best performance is still 87 Oct... Bottom line the timing and Detonation dictates the performance .. And the larger outboards have an onboard processor to control air/fuel/and timing ... So you are wizzing in the wind if you are using more than 87 Octane in a motor that is not designed for it ... And this BS ..."Well my buddy modified this and that so it would perform better with higher Octane "... ... If he totally tore it down shaved the heads, changed pistons, Changed the chip etc ... Then maybe ... But if not, Running Higher octane is more detrimental than using suggested 87 from the Mfr. ..
Ethanol ... Here is what is going on with outboards and ethanol ... Originally .. Do to the grace of our brilliant tree hugging congress and senate which actually did no research ... Enforced the ethanol ... Myself and about 4 other old outboard dealers have discussed this at end to what detriment does this have on the outboards especially the older ones I deal with ...
At first the marine industry and especially the USCG jumped in and said well all of the fuel line systems have to upgraded to meet the ethanol compatibility ... So that is why when you go to Wal-Mart to purchase a new fuel line with bulb has jumped from $12.99 to $39.99 over the past 5 years ... By the way with many type of materials which some failed ...
What myself and my fellow repair dealers have found is that the old fuel line that have been used in the past 50 years is not affected or causes any problems by using Ethanol ..
But this is what ethanol does ... Here is an example ... Your Auto ... Late model ... Fuel injected which 100% are now ... winter time .. you need a fuel additive to stop injector freeze up ... So you buy a bottle of STP Fuel de-icier ... So what is this ?? ethanol !! Ethanol absorbs water ... I can't tell you how many people that have brought their outboards to me claiming outboard Carb problems and the first thing I do is have them bring me the fuel tank and take a sample ... Straight from the fuel line ... in a clear glass bottle (usually a Miller High life Bottle, I keep a fresh supply on hand at all times.. :eek: Yep the water settles to the bottom .... So Octane is not the issue ... just stick with 87 octane unless your motor requires something different from the Mfr.
As far as Ethanol ... There are a number of oil distributors that supplies non ethanol fuel to their stations ... go on line and find them ... Now to be honest ... this is very important for older carb motors ... (the water settles in the bottom of the bowls) this is before the Ethanol enforcement ... It doesn't seem to affect the Fuel Injected newer motors ...
Now ... with all this said ... I have a 2001 4 stroke Yamaha 50 HP ... 4 carb motor ...I have run both non ethanol and ethanol through it I have seen no difference in performance ... top or bottom end ... Hope this helps ... <'TK><:)
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