Porting - higher octane needed?

[Hedgerow]

You will hear no argument from me! Id love to hear what you have to say about the subject and and advantages of using 87 vs 93 in these engines? thanks

Saws have an extremely short stroke. The hot gasses are escaping before they're completely burnt, So "Ya get what ya can, when ya can" and 87 gives it a tad quicker.. But if all a man can find in non-eth, is 91, then by all means, use 91...
Most will never notice the difference...
But gooey fuel lines suck, no matter the brand...

 

[mdavlee]

You're looking at .006 seconds between rpms at 10k like a saw will turn in the wood. The higher octane will be incomplete combustion before it's going out the muffler. Now on pipe that's stuffing some of that back in then it may not hurtopcorn:

 

[KG441c]

Ill ask this question even if elementary for some of u fellows because my mind is turning now!! If the 87 octane burns quicker and you also advance the timing a few more degrees and have quicker ignition does this equal a more efficient combustion process that equals better force downard on the piston?

 

[Jacob J.]

Most builders advance the timing some. It makes a big difference if the jug is lowered due to having been machined.

 

[XSKIER]

Also higher octane will cause hotter head temps in non race type motors,

Yeah!

 

[Hedgerow]

Ill ask this question even if elementary for some of u fellows because my mind is turning now!! If the 87 octane burns quicker and you also advance the timing a few more degrees and have quicker ignition does this equal a more efficient combustion process that equals better force downard on the piston?

Yes, to a point... Then it becomes counter productive... Fighting it's own momentum to reach TDC...
Don't ask me at what point that is though... 28 degreeish BTDC??? Randy? Jacob? Mike??

 

[HuskStihl]

87 makes more power.....

It's time consuming to explain way a short stroke engine don't need higher octane......and all I'll get is an argument.

I've quit trying.

Are you saying that I can't directly extrapolate the combustion chamber conditions from my blown 376 to my 288?! That's ******** man! An engine's an engine and saws need super hi octane!

Also higher octane will cause hotter head temps in non race type motors,

I must be a total dumbass as I had always thought the exact opposite was true

 

[mdavlee]

Yes, to a point... Then it becomes counter productive... Fighting it's own momentum to reach TDC...
Don't ask me at what point that is though... 28 degreeish BTDC??? Randy? Jacob? Mike??

I don't remember right off. Durand did a lot of testing on that part.

 

[Mastermind]

Yes he did. After 28 - 30 degrees most engines start misfiring in the cut.

 

[Trx250r180]

High octane makes big huskies hard to pull over ............




opcorn:

 

[sunfish]

Guess the high octane crowd hasn't found this thread yet.

Wish I could get 87-89 non-eth here, but the 91 non-eth is doin OK...

 

[mdavlee]

It depends on where I buy it. One place only has 87 and one has 87, 89, and 93. I've burnt over 2.5 gallons in the past 4 days milling. The last 1.5 gallons was 93. I think the leftover gallon was 87. I can't remember since I had my dad grab it on his way down the other day.

 

[Mastermind]

I would be happy with 93.

 

[KG441c]

Yes, to a point... Then it becomes counter productive... Fighting it's own momentum to reach TDC...
Don't ask me at what point that is though... 28 degreeish BTDC??? Randy? Jacob? Mike??

so advancing the timing on some stock saws will make up for the porting being off from the factory?

Guess the high octane crowd hasn't found this thread yet.

Wish I could get 87-89 non-eth here, but the 91 non-eth is doin OK...

I have 87 non ethanol about 4 miles from my house but had been driving 65 miles with cans to get 93 non ethanol

 

[Hedgerow]

so advancing the timing on some stock saws will make up for the porting being off from the factory?

I have 87 non ethanol about 4 miles from my house but had been driving 65 miles with cans to get 93 non ethanol

It's not changing the port timing any, but it will get you a little harder hit. Also buying your fuel a tad more time to release it's energy before evacuating out the exhaust port. Since it starts combusting just a tad sooner...

 

[J rod]

Advancing the timing should put more torque lower in the midrange power

 

[Ron660]

Since I only have easy access to 93 non-E octane, could my saw be adjusted to run better on 93 than 87?

 

[Mastermind]

No need 93 is fine.

It's the 101 that you really don't need.

 

[sunfish]

Since I only have easy access to 93 non-E octane, could my saw be adjusted to run better on 93 than 87?

No, it wont run better, but non-eth is better.

 

[ncsawguy]

but that high octane race gas shure does smell good,