Porting - higher octane needed?

[Deleted member 83629]

I burn all grades 87-95 E0 though it gets a nip of E10 once in a blue moon.
Don't know if im wrong of not but my trimmer runs cooler with higher octane gas than regular, well it seems like it does sure doesn't start any easier.

 

[XSKIER]

My question still would be now that we determined that 87 burns most efficiently in a saw without turning this into an oil tread is, which oil burns the most efficiently in a saw and at what ratio and protects the engine

No. 1 diesel oil has more btu per gallon than 87 octane pump gasoline. If you run 33:33:33:1 87 octane, No. 1 diesel oil, belray hr1, and one part hope, you'll get a nice boost in torque.

 

[KG441c]

No. 1 diesel oil has more btu per gallon than 87 octane pump gasoline. If you run 33:33:33:1 87 octane, No. 1 diesel oil, belray hr1, and one part hope, you'll get a nice boost in torque.[/QUOTE Lol!! Obviously I wont be running diesel in my saw but I do remeber reading a test about belray h1r and it burning alil hotter and created more energy? My question still is 87 will give an advantage over high octane in burning fuel more complete and is there an oil there ignites in the combustion process more readily than others but still offers maximum protection?

 

[blsnelling]

Does an increase in oil ratio to 32:1 slow down
the igniting process?

Lots of oil test have been done over decades. It's been proven that more oil makes more power. From what I remember, it's due to better ring seal.

Don't over complicate this. Anything from 32:1 to 50:1 will be fine in most ANY saw. I prefer to run 32:1, especially in ported saws.

 

[blsnelling]

Whats ur opinion on H1r and Motul 800t?

Those are all fantastic oils, all ester based. That's as good as it gets.

 

[KG441c]

Lots of oil test have been done over decades. It's been proven that more oil makes more power. From what I remember, it's due to better ring seal.

Don't over complicate this. Anything from 32:1 to 50:1 will be fine in most ANY saw. I prefer to run 32:1, especially in ported saws.

I believe the part about making more power but Ill still ask does more oil slow down combustion? Whether it helps like different octanes or impedes?Its just a question stuck in my mind.

 

[Marshy]

I believe the part about making more power but Ill still ask does more oil slow down combustion? Whether it helps like different octanes or impedes?Its just a question stuck in my mind.

First ask yourself, "does it matter", then by all means proceed with finding that answer.
None of us are fuel engineers, maybe start searching the interweb for answers. You will mostly get conjecture and opinion here with some smidgen of fact that are hard to detect. Hang around long enough and you will find out who knows what they are talking about.

 

[Ron660]

My co-worker, a Geologist & Engineer with previous experience blending oils and small engine testing, said octane ratings are based on something called "Compression Ratios". He said the higher the compression the more octane would be beneficial. He also said you would only need a higher octane, like 91+, if the compression ratio was 10:1 or higher. He said that would be greater than 150psi. He said there's a lot of variables in determining compression ratios but that's a good rule of thumb. Not sure if this is correct with only chainsaws but this was his experience.

 

[Mastermind]

I'm a readaholic/infomanic.....

Dig deep and study hard.

I once saw a video of a two stroke running on different fuels......87 - 110 octane.

They used an infrared camera to record the exhaust plume. With that camera you could see unburnt fuel igniting when it came into contact with the atmosphere. The 87 had about a 3" plume........the 110.......about 2'.

 

[Mastermind]

My co-worker, a Geologist & Engineer with previous experience blending oils and small engine testing, said octane ratings are based on something called "Compression Ratios". He said the higher the compression the more octane would be beneficial. He also said you would only need a higher octane, like 91+, if the compression ratio was 10:1 or higher. He said that would be greater than 150psi. He said there's a lot of variables in determining compression ratios but that's a good rule of thumb. Not sure if this is correct with only chainsaws but this was his experience.

Short stroke high compression two strokes are a breed apart......they just don't detonate easily. Longer stroke two cycle engines are different though.....that's why what we learn on a motocross bike does not apply here. It about dwell time.......

We machine the squish band and cylinder base in a way that makes these engines even more resistant to detonation.

Even automotive performance engines have changed tremendously in these last few years. Now they have new engines from the factory making 10.5:1 compression ratios, and over 500hp that will run on ****** pump gas......even on ethanol based fuels.

How did they manage that? By running a tighter quench (squish) clearance, and smaller combustion chambers.

Proper squish clearances will increase squish velocity in a manner that resists detonation extremely well. Too wide and flat, or improperly tapered, and the crankshaft will die an early death though........

If you wanna go to school on this stuff........spend some time with your nose in the literature......it's everywhere these days.

 

[HuskStihl]

Short stroke high compression two strokes are a breed apart......they just don't detonate easily. Longer stroke two cycle engines are different though.....that's why what we learn on a motocross bike does not apply here. It about dwell time.......

We machine the squish band and cylinder base in a way that makes these engines even more resistant to detonation.

Even automotive performance engines have changed tremendously in these last few years. Now they have new engines from the factory making 10.5:1 compression ratios, and over 500hp that will run on ****** pump gas......even on ethanol based fuels.

How did they manage that? By running a tighter quench (squish) clearance, and smaller combustion chambers.

Proper squish clearances will increase squish velocity in a manner that resists detonation extremely well. Too wide and flat, or improperly tapered, and the crankshaft will die an early death though........

If you wanna go to school on this stuff........spend some time with your nose in the literature......it's everywhere these days.

The infinitely better electronics and the cooling effects of direct injection have helped a bunch as well

 

[Marshy]

My co-worker, a Geologist & Engineer with previous experience blending oils and small engine testing, said octane ratings are based on something called "Compression Ratios". He said the higher the compression the more octane would be beneficial. He also said you would only need a higher octane, like 91+, if the compression ratio was 10:1 or higher. He said that would be greater than 150psi. He said there's a lot of variables in determining compression ratios but that's a good rule of thumb. Not sure if this is correct with only chainsaws but this was his experience.

Determining compression ratios are straight forward no variables involved. The compression of a cylinder (150 psi) will not tell you what the compression ratio is. The compression ratio is the ratio of volume of the combustion chamber with piston at BDC vs TDC.

Describing MON octane testing, straight from ASTM D2700 - 13b

http://www.astm.org/Standards/D2700.htm

Scope
1.1 This laboratory test method covers the quantitative determination of the knock rating of liquid spark-ignition engine fuel in terms of Motor octane number, including fuels that contain up to 25 % v/v of ethanol. However, this test method may not be applicable to fuel and fuel components that are primarily oxygenates.2 The sample fuel is tested in a standardized single cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions. The octane number scale is defined by the volumetric composition of primary reference fuel blends. The sample fuel knock intensity is compared to that of one or more primary reference fuel blends. The octane number of the primary reference fuel blend that matches the knock intensity of the sample fuel establishes the Motor octane number.
1.2 The octane number scale covers the range from 0 to 120 octane number, but this test method has a working range from 40 to 120 octane number. Typical commercial fuels produced for automotive spark-ignition engines rate in the 80 to 90 Motor octane number range. Typical commercial fuels produced for aviation spark-ignition engines rate in the 98 to 102 Motor octane number range. Testing of gasoline blend stocks or other process stream materials can produce ratings at various levels throughout the Motor octane number range.

 

[Mastermind]

The infinitely better electronics and the cooling effects of direct injection have helped a bunch as well

Direct injection exists in very few engines at this point.......

 

[Marshy]

Direct injection exists in very few engines at this point.......

Not anymore. My 2012 Chevy Traverse uses a direct injected 3.6L V6 and has 281hp and 261ft-lbs. That is the base engine for Chevy Traverse and Equinox and for their GM twins...

Looks like the 2014 models are making 300 hp and over 270 ft-lbs...

 

[Mastermind]

Chevy is setting the standard......

Their newest Corvette engine is a masterpiece.....

 

[Fumducker]

Would low octane fuel be ok in high elevation. 8000' and above. I switched to high octane because it seemed like my saws didn't run well on 87. Now I'm using av gas. Am I wasting my money?


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[Trx250r180]

ok why does my old 440 mopar ping like hell off pump gas then ?

 

[Mastermind]

Open chamber design........

 

[Chris-PA]

Direct injection exists in very few engines at this point.......

It's actually everywhere now, as are knock sensors. That's not to say combustion chamber shape isn't also important. Still, one has to be careful about specs, as even with knock sensors, direct injection, variable valve timing, etc., some of these cars only get the advertised power/economy with premium fuel. But there is a world of difference between such 4-strokes and these little 2-strokes - some things are relevant to both, some are not.

 

[J rod]

The older engines like your Mopar required lead gas and gas back then had a lot more additives, those motors also could have had dome pistons higher compression ratios, ect..