Stihl timbersports stock saws

[rmihalek]

Does anyone know what is done at the Stihl Timbersports competition to ensure that all the stock saws perform the same? Are these saws all broken in at the same time, maybe even have the compression tested to be within a certain percentage of one another? Does each saw get precisely the same amount of fuel run through it before the competition?

Is Simonizer there to check the BMEP, pressure gradients, latent heat of vaporization, etc.?

 

[Simonizer]

Does anyone know what is done at the Stihl Timbersports competition to ensure that all the stock saws perform the same? Are these saws all broken in at the same time, maybe even have the compression tested to be within a certain percentage of one another? Does each saw get precisely the same amount of fuel run through it before the competition?

Is Simonizer there to check the BMEP, pressure gradients, latent heat of vaporization, etc.?

Hey cool. Do you know what these terms mean?

 

[timberwolf]

I would say he does, and could explain them to you in detail if you were wondering.

 

[Simonizer]

I would say he does, and could explain them to you in detail if you were wondering.

That would be nice. I don't really know stuff about things

 

[timberwolf]

Sorry, I missed something, How do you do all that saw work and get results without having a handle on those sorts of concepts, just thought you were taking a poke, or maybe you were just jabbing back, fair enough.

 

[Simonizer]

Sorry, I missed something, How do you do all that saw work and get results without having a handle on those sorts of concepts, just thought you were taking a poke.

It's called sarcasm. Stay with the tour TW.

 

[Arden Cogar Jr.]

To my knowledge ,and I honestly have no idea what I'm talking about, four saws are selected straight off the assembly line. They are MS 660s. 25" bars and new RS Chains right off the spool are put in place. From that, the technician, Matt Rose, takes the saws, uses a "dynomitor" and tests it under load and a bunch of other stuff that I can't remember. He dials each saw into the same RPMs under load, I think. Then, I believe he makes an equal number of cuts in the wood with the saws and has someone time the cuts. From then the times are averaged and the slowest and the fastest saw are thrown out. The two saws in the middle are kept.

Again, I think this is how it works.

All the best,
Jamie

 

[rmihalek]

Thanks Jamie. It was a lot less complicated than I thought. Still seems like there might be some room for error, but I guess nothing is perfect.

Simon, I have a vague text-book like idea of what those terms mean, but no working knowledge of how they are interrelated regarding engine performance. In other words, going back to one of the first posts you made on this forum, you stated how poor the BMEP is on saws compared to motocross engines. I've wondered the same thing myself. Why can a CR/KX/YZ/RM 80 putting out close to 20hp when a 79cc Dolmar can't do half of that? Okay, water cooling versus air cooling is one thing, pipe versus no pipe, and as Russ mentioned, the duty cycles are different, but still!

So, what can be done (if anything) to a stock saw to get motocross-like BMEP?

 

[Simonizer]

Thanks Jamie. It was a lot less complicated than I thought. Still seems like there might be some room for error, but I guess nothing is perfect.

Simon, I have a vague text-book like idea of what those terms mean, but no working knowledge of how they are interrelated regarding engine performance. In other words, going back to one of the first posts you made on this forum, you stated how poor the BMEP is on saws compared to motocross engines. I've wondered the same thing myself. Why can a CR/KX/YZ/RM 80 putting out close to 20hp when a 79cc Dolmar can't do half of that? Okay, water cooling versus air cooling is one thing, pipe versus no pipe, and as Russ mentioned, the duty cycles are different, but still!

So, what can be done (if anything) to a stock saw to get motocross-like BMEP?

Nothing unfortunately. We can make substantial gains but it is what it is. There is a point at which we start to fight scavenging effects by advancing the exhaust timing with actually, (and it's easy to picture) venting the combustion charge too early. This is just another optimization problem. Increasing intake duration by changing the height, (and sometimes width) of the intake port gives us a better charge to counter-act this and increases fuel consumption with the HP increase of course. An expansion chamber makes a huge difference because it incorporates resonance and believe it or not has a vacuum like effect on the other end. Like a turbo only inversed. Due to the fixed volume of expansion chambers, this happens over a narrow rpm band. Variable volume expansion chambers with servo-control operated baffles coupled to a frequency-counter driven from the ignition system can vary this resonance over a broader spectrum. The whole time we are trying to keep the stoichiometry at about 14.7:1 for a proper combustion process. Keeping in mind everything is happening 200 times per second this becomes a very delicate balancing act. But I digress,...

 

[ShoerFast]

Best poer at 14.7 :1 ?

The whole time we are trying to keep the stoichiometry at about 14.7:1 for a proper combustion process. Keeping in mind everything is happening 200 times per second this becomes a very delicate balancing act. But I digress,...

So your saying that your achieving Best Power at 14.7 : 1 ?

Kevin

 

[rmihalek]

That's 14.7 pounds (or kilos) of air for each pound (or kilo) of fuel. It's the optimum ratio for combustion but some sources claim not for a heavily loaded engine since it's too close to the point of detonation.

 

[Simonizer]

So your saying that your achieving Best Power at 14.7 : 1 ?

Kevin

That is not compression ratio, that is air to fuel ratio. Like any chemical reaction, there is a mole to mole ratio that is required. Sometimes catalysts are involved to accelerate this reaction but they do not have a net effect on the reaction.

 

[ShoerFast]

It's a yes or no answer,,,,,,,

That is not compression ratio, that is air to fuel ratio. Like any chemical reaction, there is a mole to mole ratio that is required. Sometimes catalysts are involved to accelerate this reaction but they do not have a net effect on the reaction.

So your're saying that your achieving Best Power at 14.7 : 1 ? ,,,,,, air to fuel ratio? If I may ask?

 

[Simonizer]

So your saying that your achieving Best Power at 14.7 : 1 ? ,,,,,, Fuel to air ratio? If I may ask?

No, air to fuel ratio. Stay with the tour please. And it's "you're" not "your".

 

[ShoerFast]

Thats how I thought your anwser would go, if there is anyone that thinks that there coming anywere close to best power at 14.7 : 1 , they had best stick to correcting grammar!

 

[klickitatsacket]

The only people who are interested in a saw running at 14.7:1 are the EPA and environ "mental" ists. If you are running a tuned pipe it is the last thing you want.

 

[badcars2]

u go dean. let the smoke roll!!!!!!

 

[ShoerFast]

Dean
Yes, unless you're making this stuff up from some How to Win friends and sound like a Mechanic, book, wouldent you say that 14.7 : 1 is somewere at the extreme bottem of the transfer slot?
Kevin

 

[klickitatsacket]

A stoichiometric ratio of 14.7:1 is an Ideal ratio for 100% combustion of the fuel and is not an ideal condition for HP or lubrication of a 2 stroke motor. Unless you have lots of money to burn running your saw lean is not a good idea. Besides if you are running a pipe; I believe you are more concerned with HP than emissions.

 

[rmihalek]

Maximum HP is produced at around 12.5-13.3:1 air:gasoline ratio, according to various sources I've read on the internet. I don't have equipment to verify this independently. Other fuels, like nitromethane and alcohol, bring oxygen with them and consequently require less "air" (oxygen) for proper combustion. I think nitromethane runs around 3:1 air:fuel, about four times as "rich" as gasoline.