I'm wondering if anyone has had experience using 87 octane fuel in Yamaha 250 hp 4 stroke engines. Yamaha recommends 89 Octane fuel for these engines, but it is unavailable at many fuel docks (leaving a choice of 87 or 91 octane). I've heard that using 87 octane may result in a slight power loss but otherwise would be fine. I'd appreciate any thoughts or advice.
Fuel - Yamaha 250hp
- Thread starter awc4kds
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Often times the only difference between horsepower ratings on the engines is the use of higher octane fuel. Even though the Yamaha F250 TXR has variable valve timing it's the fuel that gets the extra 25 HP as opposed to the F225. Unless you burn an awful lot of fuel it wouldn't be worth the savings in my opinion. It would be a little penny wise and pound foolish but that's just my opinion.
wahoo33417
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I have been forced to put in 87 octane once while on a trip and found no ill affects and felt no loss of power. But like Chris said, I would not make a habit of it. It may do no harm, but for me, not worth the chance. Requiring 87 octane isn't a selling point, so I presume Yamaha makes it a requirement for a reason. It would be nice if they would share what that reason is.
Rob
Rob
Gman25
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capt chris said:
So if someone has an F225 and they use a high octane fuel its like having an F250?????Did I read that right???
I would check with Yamaha on that one, but if you look at the major specs on the motors there is not a lot of difference other than the variable camshaft timing and the required fuel octane. Displacement, compression ratio, etc all identical. Maybe they tweak the micro chips or something, I don't know. Best to ask Kennesaw.Gman25 said:
wahoo33417
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Gman25 said:
I'm sure it does not work that way. Like a car, putting in higher octane than needed does no harm but it does no good, either.
Using a fuel with a higher octane lets an engine run at a higher compression ratio without having problems with auto-ignition (knock).
Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber.
If I understand it correctly, variable valve timing allows the ignition timing to be retarded, allowing more fuel and air to be crammed into the cylinder, without the risk of auto-ignition.
Without the ability to retard the timing on demand, the engine doesn't take advantage of the higher octane.
Such is my understanding - limited though it may be.
Rob
it comes down to compression ratio and PSI in the cylinders
more comp,PSI = hotter inside
run a higher octane to cool it down
more comp,PSI = hotter inside
run a higher octane to cool it down
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HP
I remember when I got my 250 SWS, the sales guy talked about the common theme here, that the 225 SWS had to be tuned back B/C of the amount of power it put out vs. the 250. Can't explain specifically why, but is it because they started with the same block size and the fine tuning dictated H.P.?
I remember when I got my 250 SWS, the sales guy talked about the common theme here, that the 225 SWS had to be tuned back B/C of the amount of power it put out vs. the 250. Can't explain specifically why, but is it because they started with the same block size and the fine tuning dictated H.P.?