93 octain gas why not?

[catfish Rick]

I have a 9.5 Johnson i just bought its in very good cond and runs great don't know what year it is yet but the top looks like a turtle, I know the mixture is 50:1 I've been using 93 oct gas in it and they told me not to do that to run 87 oct, do any of you know why, i figured better gas = better running, thanks for the responces.

 

[rolmops]

Re: 93 octain gas why not?

Your engine would not know what to do with that high an octane.Not that it would hurt it any,but it is just a waste of money.

 

[JB]

Re: 93 octain gas why not?

High octane does not mean high quality, Rick. It merely means better able to tolerate high compression, which 2 strokes do not have.<br /><br />Many believe that the extra additives in premium increase deposits. I don't think so, but I do know that high octane thins your wallet a lot faster than regular.

 

[sparkroost]

Re: 93 octain gas why not?

At what compression would require 92 octane?(at factory timing)

 

[Cricket Too]

Re: 93 octain gas why not?

I remember hearing something about 93 octane having a certain type of alcohol in it that was bad for rubber parts in carbs and other parts of fuel systems.

 

[Cricket Too]

Re: 93 octain gas why not?

JB....what is the reason that 2 strokes don't run high compression? It is something I have always wondered about but never found out why. Thanks.

 

[Dhadley]

Re: 93 octain gas why not?

Todays high test, unlike hi test in the past, burns hotter -- not cooler. The number one enemy of 2 stroke pistons is combustion heat. <br /><br />Once you increase the compression of a 2 stroke outboard there is a point at which you will need to run higher octane. That number is different for each motor as it depends on port timing, port area, squish band, pocket shape, spark plug location, the timing edge on the piston, back pressure, cooling capacity and so on.<br /><br />As you increase compression (which raises combustion temps) you have to flow more fuel (to cool the combustion to an acceptable point).<br /><br />Ain't this fun?

 

[Chinewalker]

Re: 93 octain gas why not?

Actually there are a lot of 2-strokes that do run high compression in high-performance applications. If you shave the heads and increase compression ratio, you might have to go up in octane to keep it from detonating. High performance Mercs recommend high-test, and some require Av-gas. The reason your run-of-the-mill motors aren't higher compression is reliability. The higher compression, the more stress on the motor's internals. You can build motors that handle it, but it's more costly, so they've come to a happy medium where the motors run on regular gas and maintain a semblence of reliability...<br />- Scott

 

[Cricket Too]

Re: 93 octain gas why not?

Thanks for the info Chinewalker, appreciate it.