Fuel useage good or bad for a 2 stroke.

[blacklab99]

The manufacturers also advised against using synthetic 2 stroke oil and 4stroke engine oil, well, until they brought out their own synthetic oils that is. I have never seen any engine damage caused by use of a higher octane fuel in something with 91 octane recommended, (in 30 years of working on engines), and as for manufacturers, sometimes they don't give us all the information, just what they think we need to know, it's not always to the benefit of the consumer

I agree with you from my experience 100 % PJ

But, at the end of the day, when an outboard manufacturer specifies using 91 octane,
Its them that warantee the engine, not you or me ! they will try to get out of any failures if they can, so why give them an out,
So my recommendation for new engines, be it out board or car,
Use what the manufacturer recommends !!, either oils or fuel.

A footnote, Not all engines can be lumped into that, I've seen catstrophic engine failure by wrong octane levels used in race engines,
But I understand that's not what we are talking about here......

Col

[frozenpod]

That's true Purple, the burn is slower and cooler compared to 91, but it's micro second stuff.

But it does pose the question, why do 2 stroke engine manufacturers advise against and recommend lower octane ?
I in all honesty cant see the difference when using it with a 2 stroke engine.
If manufacturers of 4 stroke engines specify ( as most japanese manufacturers do) 91 octane, my advice, stick to what they state, for obvious reasons.

Col

Not sure they do Col, local dealers and local mechanics might but I have never seen the manufacture advise against higher octane fuel for carby 2 strokes.

Keep in mind when carby 2 strokes were designed when we had leaded fuel which was 96 octane.

The manual for my old carby 2 stroke recommended minimum 93 (when converted to octane) and it ran like a dog on 91 (after we could no longer use leaded fuel) particularly when the fuel was more than 1 month old. Put in 94/95 and it ran great and still ran great when the fuel was 1 month old.

The same applies to the replacement carby 2 stroke (in terms of how it runs with 91 vs 94/95) that was purchased after leaded fuel was long gone.

I strongly recommend using BP premium fuel!


On top of this it is pretty much impossible to buy 91 without ethanol. Unless you using your boat a lot ethanol is the last thing you want to sit in your tank over winter. No issues with E10 if you are going through the fuel during summer ect only when left to sit for 1 month plus typically over winter.

[purple5ive]

https://www.tradeboats.com.au/trailerbo ... -aint-fuel

[blacklab99]

Hi Frozen, as mentioned before, I totally agree with you.

However, I actually question whether a 2 stroke out board can even benefit largely from the premium fuels at all.
Premium, as you know, burns longer and more pronounced, it was specifically designed to be used in engines with variable timing so as they can take advantage of the longer burn time, obviously 2 stroke aren't or you wouldn't alter timing to compensate for premium use.
Obviously cars can take advantage of this with VVT, so the only benefit in my eyes would be the added cleaning side of the premium fuel, cleaner carby parts etc, that is why they say or warn about the fact that the extra unburnt fuel, because of the timing "can wash the bores".
Is there a real benefit versus the extra cost ? I seriously doubt it in all honesty, but I don't think it does any damage at all.
It does seem to get the response from people to say my engine runs better on premium, i've felt that when I've put it thru 2 strokes that I've had in the past, but 2 strokes aren't really set up to take its designed for benefits, plus the fact the fuel is so diluted with 2 stroke oil, its design benefits again are compromised. It holds a higher octane rating for longer than 91 would, so thats got to be a better thing.
As a foot note, using premium in my old British bikes, to gain its benefits, I have to time the engine to suit, again, no VVT on those old girls.
So I say, if you think it runs better, pay the extra, if you use 91, just make sure you never store it for to long, either fuel used, your boat engine will work,,, stale fuel is our enemy..............

More importantly Frozen, are you wetting a winter line ?

Col

[smile0784]

Im trying to get frozenpod out on the boat but hes always busy lol

[frozenpod]

Fishing in winter is great. Been out a couple of times but not enough. Fishing has taken a backseat to work and racing this year. Hard to do it all was at Sandown this passed weekend and have massive race early July.

Main difference between 91, 95 and 98 is resistance to detonation.

Higher octane allowing for greater compression and ignition timing. Thus producing more power and greater efficiency.

VVT allows for more optimal camshaft timing over a wider range added benefit is lower dynamic compression allowing for higher static compression. Not directly related but certainly indirectly related to performance of modern engines.

The burn rate as you say is slightly different which also helps smoother running more power and better economy of 95 over 91. You end up with a more complete burn and less deposits but this is a small difference.

Basically within reason higher octane is better for everything. But you could reach a point where plugs foul roughly around 115.

[PJ72]

Main difference between 91, 95 and 98 is resistance to detonation.

Higher octane allowing for greater compression and ignition timing. Thus producing more power and greater efficiency.

VVT allows for more optimal camshaft timing over a wider range added benefit is lower dynamic compression allowing for higher static compression. Not directly related but certainly indirectly related to performance of modern engines.

The burn rate as you say is slightly different which also helps smoother running more power and better economy of 95 over 91. You end up with a more complete burn and less deposits but this is a small difference.

Basically within reason higher octane is better for everything. But you could reach a point where plugs foul roughly around 115.

Well said, I will back you up with recommending BP fuels, especially if you have a diesel (due to them having a higher Cetane rating than other companies, -similar to an octane rating)
Froze pod, what do you race? Car/class?

[frozenpod]

Well said, I will back you up with recommending BP fuels, especially if you have a diesel (due to them having a higher Cetane rating than other companies, -similar to an octane rating)
Froze pod, what do you race? Car/class?

I had a few different cars and I used to race in the supersprint championship with modified street cars (somewhat a new name for improved production.) As well as timed and untimed club run track days.

Last Sunday was the first time I have been at the track in a few years. I was assisting and spectating only as I couldn't get a last minute entry.

[PJ72]

I had a few different cars and I used to race in the supersprint championship with modified street cars (somewhat a new name for improved production.) As well as timed and untimed club run track days.

Last Sunday was the first time I have been at the track in a few years. I was assisting and spectating only as I couldn't get a last minute entry.[/quote]

Cool, was going to venture into racing about 10 years ago, but the wife said 'boat or car, can't have both'
Still trying to get the car as well though