Question about fuel efficiency vs. performance

[TJ the Chainsaw Mechanic]

Hotter Spark plug.

 

[Al Smith]

Here's another thing on those giant holes .Timberwolf AKA Brian Wright had a spread sheet presentation on muffler holes as a percentage .He found that much over 80 to 85 percent of the area of the exhaust port added almost nothing to performance.He took it out to 125 percent if I recall correctly .Just sayin

 

[Mastermind]

Here's another thing on those giant holes .Timberwolf AKA Brian Wright had a spread sheet presentation on muffler holes as a percentage .He found that much over 80 to 85 percent of the area of the exhaust port added almost nothing to performance.He took it out to 125 percent if I recall correctly .Just sayin

I remember that too Al.

 

[Simondo]

Here's another thing on those giant holes .Timberwolf AKA Brian Wright had a spread sheet presentation on muffler holes as a percentage .He found that much over 80 to 85 percent of the area of the exhaust port added almost nothing to performance.He took it out to 125 percent if I recall correctly .Just sayin

I as well believe there is a point where its worth stopping. Now i don't profess to have the understanding of the subject in full but" without" the sort of detailed port and time-work done by some of the fellers here..i tend to go for 70-75% of exhaust port sq aria as my muffler output hole size. It always tends to be a very large increase in the standard output anyway.

 

[Al Smith]

Let me give another example .Zander down in Cincy had a brand new o88 he was proud as a peacock of but got the bright idea to hog out the muff.Then he was really proud .Some outlandish hole,like 150 percent .I as well as others cautioned him to at least crank out the high speed so he could get some fuel to it .He didn't. About 2 weeks later,low hours 088 Stihl on flea bay,cooked cylinder,Cincinnati Ohio .

 

[Terry Syd]

Tune for what you want.

 

[Terry Syd]

From Wikipedia - A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher efficiency is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. It may be more helpful to think of it as an "expansion ratio", since more expansion reduces the temperature of the exhaust gases, and therefore the energy wasted to the atmosphere. Diesel engines actually have a higher peak combustion temperature than petrol engines, but the greater expansion means they reject less heat in their cooler exhaust.

 

[Brush Ape]

With a longer blow down it only makes sense it will blow some fuel straight through it

Longer blowdown spitting fuel out of the muffler?

Got that backwards brother Al?

With all due respect, I'm going to have to agree with Al.

 

[Onan18]

With all due respect, I'm going to have to agree with Al.

What you did there, I see that.

 

[paragonbuilder]

With all due respect, I'm going to have to agree with Al.

Lol

 

[RI Chevy]

One can't go wrong. Lol

 

[Brush Ape]

If you don't know your ass from a hole in the ground like me, just hedge your bet.

 

[Stihl036]

Ill be the first to say i couldnt care less how much fuel my saw uses (within reason). I dont climb trees or do production felling, and i understand the utility of fuel efficiency for those guys, but, for cutting firewood and occasional felling, im usually ready for a break before my saw is, so burn it all!!

Fuel efficiency don't matter much to me either but I do wonder about the effects of years of breathing unburnt fuel. Not to derail the subject but for the past few years I've noticed that two stroke smoke burns my eyes worse than I remember it doing when I was younger. I'm 60.

 

[Stump Shot]

I think the variable not looked at is time. While some high performance modifications can lead to more efficiency to a point, an engine that has it's work done in a faster manner and is turned off burns no more fuel. So even though it is technically burning more fuel at the moment, it is also producing more work at that moment, leading to a shortened run time evening out in the end.

 

[junkman]

This is a great discussion .

 

[MustangMike]

My thoughts are similar to several expressed above. Increasing compression and advancing timing may be making the saw more efficient, and you excellent porting improves performance.

As Randy said, why would you change a thing (unless you are building a cant saw).