Torque, RPMs, Porting...My Philosophy

[blsnelling]

The exhaust is a huge bottleneck on these choked up saws.

 

[HuskStihl]

Can you show that cubic relationship of power with .... what? (i.e. an equation or somesuch)? The number of cutters passing a point will go up proportionately with increased chain speed, and that is the main load, so it would seem that the power required also increases linearly/proportionately. Certainly there will be other losses that increase and so in reality you will need more than a 10% increase in power, but mechanical engineering classes were a long time ago and I can't come up with a 3rd order relationship.

I bet the above post as well as the one it is in response to are both fairly accurate. The power thing comes from car world and top speed, again, no direct equation, but a well known fact that doubling power won't double top speed. Assuming a "cubic" relationship, a 10% increase would require roughly a third more power. For example, 100hp car max speed 100mph, to get 110 would require 135ish. To get 200mph it would need 800bhp. Obviously not a perfect equation, and likely cannot be directly extrapolated to saws, but a decent rough approximation. The graph of power to speed will become asymptotic well before einsteinian levels, but that topic has been well covered in the "not so pro" thread

 

[Mastermind]

Chads dyno will make guessing moot, but I'd bet the latest 660's problem lies more in the cylinder than the exhaust

I think it's both Jon.

The high exhaust, and tiny outlet seems like a way to burn more hydrocarbon in the muffler can.

Just a way to make the EPA happy.

 

[Chris-PA]

I bet the above post as well as the one it is in response to are both fairly accurate. The power thing comes from car world and top speed, again, no direct equation, but a well known fact that doubling power won't double top speed. Assuming a "cubic" relationship, a 10% increase would require roughly a third more power. For example, 100hp car max speed 100mph, to get 110 would require 135ish. To get 200mph it would need 800bhp. Obviously not a perfect equation, and likely cannot be directly extrapolated to saws, but a decent rough approximation. The graph of power to speed will become asymptotic well before einsteinian levels, but that topic has been well covered in the "not so pro" thread

That could be - in which case the cubed term would come from aerodynamic drag, but that is not really applicable here. Well, some of the chains we see might have some air resistance!

 

[Trx250r180]

I think it's both Jon.

The high exhaust, and tiny outlet seems like a way to burn more hydrocarbon in the muffler can.

Just a way to make the EPA happy.

i tried a stock muffler on the 660 to try to quiet it down ,tuned correctly it was getting hot enough milling to burn the paint and discolor the front cover ,i pulled the muffler cover ,much dryer than i felt comfortable with milling in there from the heat ,muffler was very clean actually ,i can see the epa thing here for cleaner burning exhaust ,slapped just a dual port cover on there with no carb adjustments ,had oil in the muffler can now ,you would think with more airflow it would have to be richened up ,but it ran cooler and the piston was actually wetter just by putting the cover on

 

[Mastermind]

I gotta share something here........

We all like to think that we are building saws that are the strongest, fastest, meanest, etc.....

I have another consideration. After all, I just build saws for work.

Safety.

The days of getting every ounce of power I can find out of the work saws I build are pretty much over......and have been for a while now.

That's not something I really post about, but there it is. Can I make a saw that's a little faster? Oh yeah......I call those "extra spicy".

Here's the thing though.......a guy starts the backcut on a heavy head leaner.......the ultra high compression finely tuned "on the edge" machine in his hands decides to take a dump......

That's a bad day.

I still build the "extra spicy" saws for guys that want a "GTG" saw. But my true work saws are a little different. Toned down a wee bit....

These days I'm looking at ways to make them perform at least 30% better than stock, while keeping the unit as quiet as possible. Fuel economy is also a consideration, but most importantly is the unit's dependability.

Just keeping it real.......

 

[MustangMike]

And that is why it is so difficult to place the real value on experience. Sounds perfect.

 

[hardpan]

Perfect recipe and logic.

 

[Hinerman]

I gotta share something here........

We all like to think that we are building saws that are the strongest, fastest, meanest, etc.....

I have another consideration. After all, I just build saws for work.

Safety.

The days of getting every ounce of power I can find out of the work saws I build are pretty much over......and have been for a while now.

That's not something I really post about, but there it is. Can I make a saw that's a little faster? Oh yeah......I call those "extra spicy".

Here's the thing though.......a guy starts the backcut on a heavy head leaner.......the ultra high compression finely tuned "on the edge" machine in his hands decides to take a dump......

That's a bad day.

I still build the "extra spicy" saws for guys that want a "GTG" saw. But my true work saws are a little different. Toned down a wee bit....

These days I'm looking at ways to make them perform at least 30% better than stock, while keeping the unit as quiet as possible. Fuel economy is also a consideration, but most importantly is the unit's dependability.

Just keeping it real.......

Thank you

 

[redfin]

Would you by chance have any (extra spicy) recipes for a 288? I'm gonna try my hand at a pipe. It will probably be ugly because my tig skills aren't that great yet.

 

[blsnelling]

Porting for a pipe is totally unlike what would go in a GTG saw.

 

[Hedgerow]

I gotta share something here........

We all like to think that we are building saws that are the strongest, fastest, meanest, etc.....

I have another consideration. After all, I just build saws for work.

Safety.

The days of getting every ounce of power I can find out of the work saws I build are pretty much over......and have been for a while now.

That's not something I really post about, but there it is. Can I make a saw that's a little faster? Oh yeah......I call those "extra spicy".

Here's the thing though.......a guy starts the backcut on a heavy head leaner.......the ultra high compression finely tuned "on the edge" machine in his hands decides to take a dump......

That's a bad day.

I still build the "extra spicy" saws for guys that want a "GTG" saw. But my true work saws are a little different. Toned down a wee bit....

These days I'm looking at ways to make them perform at least 30% better than stock, while keeping the unit as quiet as possible. Fuel economy is also a consideration, but most importantly is the unit's dependability.

Just keeping it real.......

And use a sharp chain...

But I still like the extra spicy ones from time to time...

 

[Hedgerow]

Porting for a pipe is totally unlike what would go in a GTG saw.

Though pipes can be made in all form and fashion...
Hence the term "tuned pipe"...

When someone is porting a saw to be run on pipe, is the standard M.O. to have an extremely high exhaust and insane intake duration?

 

[blsnelling]

In the last 5 years or so, I think I've only had 5 or 6 different saws fail. Three of those were saws that I had built for myself, which also had aftermarket topend on them. I will not port an AM topend for a customer. So when it really comes down to it, I've really only had a couple different saws fail. I don't see reliability as a real concern. My biggest concern is an operator tuning and using the saw properly. Fortunately, that hasn't been a problem either.

 

[blsnelling]

Though pipes can be made in all form and fashion...
Hence the term "tuned pipe"...

When someone is porting a saw to be run on pipe, is the standard M.O. to have an extremely high exhaust and insane intake duration?

The exhaust is much higher and it will have much more blowdown. You want to keep static compression reasonable too.

 

[Hedgerow]

The exhaust is much higher and it will have much more blowdown. You want to keep static compression reasonable too.

I wondered about having too little blow down in a saw meant for work... And it possibly messing with what the pipe was trying to do..

 

[blsnelling]

A piped saw will likely have >30° of blowdown.

 

[MasterMech]

In the last 5 years or so, I think I've only had 5 or 6 different saws fail. Three of those were saws that I had built for myself, which also had aftermarket topend on them. I will not port an AM topend for a customer. So when it really comes down to it, I've really only had a couple different saws fail. I don't see reliability as a real concern. My biggest concern is an operator tuning and using the saw properly. Fortunately, that hasn't been a problem either.

And should be less of a problem going forward thanks to AT/MT. I bet you guys with grinders are sleeping good at night when one of those gets sent home.

 

[redfin]

Porting for a pipe is totally unlike what would go in a GTG saw.

Does that mean you have a good recipe?

 

[blsnelling]

Does that mean you have a good recipe?

I've never ported a 288. That would be better served in another thread too.