Porting torque vs hp

[Chainsaw Jim]

Either,makes no difference but it has a oem 064 muffler and dp cover.
If I replaced the cover with a solid one it kills them also. I know now how much they need. Can't be to open or to restricted.

Are you noticing any differences with outlet locations when you add a second port to the muffler?

 

[MustangMike]

Timing is a part of it but not all of it

And I was not referring to just timing, but that also. I imagine the size of the ports should match (somewhat) the cc s of the saw, but like Randy stated, even the shape makes a difference.

 

[jmssaws]

Are you noticing any differences with outlet locations when you add a second port to the muffler?

All I have tried is dp covers

 

[jmssaws]

And I was not referring to just timing, but that also. I imagine the size of the ports should match (somewhat) the cc s of the saw, but like Randy stated, even the shape makes a difference.

The shape of the exhaust roof is very important for power and the shape of the transfers are as well.

 

[MustangMike]

Maybe it's the opposite with dirt bikes. When I put a big bore kit on my 250f (same stroke, bigger bore) I got a ton more bottom end with no gain on top end.

I'm not surprised, the larger engine will generally do that. However, in general, when they want high RPM performance, they keep the stoke short for higher RPMs, and adding stroke was always a way to get more torque (like putting a 428 crank in a 390 block to get a Mercury 410 motor). A larger displacement with the same cam/heads will produce power at a lower RPM range.

Also, the 427 Ford engine was built for high speed, the 428 for torque ... the 427 had a larger bore, the 428 a longer stroke (the 428 was not initially designed for high performance, it initially had 390 heads and was used to tool large heavy Thunderbird's & cop cars around.

I am also talking old school, new materials have made the old laws of physics almost non relevant. The higher strength parts are almost indestructible, but back in the day ... these things mattered.

 

[RIDE-RED 350r]

Well I guess if there were no mystery to it, there would be no fun either. Definitely not as easy as changing a camshaft to get a pretty much known result.

Porting a 2-stroke is very much like changing a cam... The porting layout in a 2-stroke basically does the same thing a cam does in a 4-stroke, only with more voodoo! LOL!

 

[Chainsaw Jim]

All I have tried is dp covers

You'll have to try a solid cover and add a second opening to the flywheel side as far back as possible with a bolt on deflector. Improving the sound wave reflecting surface may allow you to use the flow you originally intended which will increase hp.

 

[jmssaws]

I believe that the cylinder is flowing all it can and that's why the big carb and boot done nothing,even with it the muffler couldn't be opened.

Also it's not like I'm really restricting it,the openings a both large,probably 200%

I feal that it's pretty well optimum plus it doesnt bother me to grind less on a muffler or to have a quieter saw
Also not everyone is exactly the same so the muffler basically needs tuned for the saw.

 

[paragonbuilder]

You'll have to try a solid cover and add a second opening to the flywheel side as far back as possible with a bolt on deflector. Improving the sound wave reflecting surface may allow you to use the flow you originally intended which will increase hp.

Sort of like a mini pipe?


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[mdavlee]

I am going to disagree with the bore/stroke statement. Generally, when they want torque, they increase the stroke, and a high RPM motor will often have a large bore & short stroke, the piston travels a lot slower that way.

661 stock for stock has more torque than the 660. Bigger bore and shorter stroke.

 

[mdavlee]

And I was not referring to just timing, but that also. I imagine the size of the ports should match (somewhat) the cc s of the saw, but like Randy stated, even the shape makes a difference.

Not really. Look at a 7900 jug and you'll be really baffled it could make that much power with transfers the size of a 346.

 

[RIDE-RED 350r]

Not really. Look at a 7900 jug and you'll be really baffled it could make that much power with transfers the size of a 346.

Intake and transfer velocity the driving force there??

 

[huskihl]

Intake and transfer velocity the driving force there??

It's got a small case. A higher percentage of what goes in the bottom ends up on top every stroke

 

[Locust Cutter]

I build a lot of saws for guys in OZ. They don't want a high rpm saw. Now, I've made the mistake of going overboard on torque too, so I get where Jason is coming from too.

I reckon it's about finding out what sort of saw the customer is looking for.

Running in the same wood, cutting the same amount, the 9010 will keep a sharp chain longer than my 372 will. It just beats the hell out of the cutters. Put the same bar an loop on the 9010 and it lasts longer. It also cuts slower but not much.

 

[RIDE-RED 350r]

It's got a small case. A higher percentage of what goes in the bottom ends up on top every stroke

Aha! So there is more than just convenience of easy upgrade by putting a 7900 topend on a 6400 case? Just a stab in the dark here, but that kind of leads me to think that the 6400 came first and the 7900 is a factory "big bore"?

 

[Al Smith]

Not really. Look at a 7900 jug and you'll be really baffled it could make that much power with transfers the size of a 346.

Likewise if you look at the transfers on an 084 compared to cylinder size then look at the transfers on a 200T . The 200 by that reference is huge .---time /area /open -----

 

[Chainsaw Jim]

Sort of like a mini pipe?


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More like muffler tuning to complete the intended improvement of a build when necessary. One example of a shop that understands this is Walkers. Many have taken a saw to them to have "hopped up" then complained after getting their saws back with only a muffler mod...but notice they still brag about the saws performance.

 

[jmssaws]

661 stock for stock has more torque than the 660. Bigger bore and shorter stroke.

It also has more hp than a 660 but it's also quads

 

[Fairways_and_Greens]

Did you change the rod also?

Nope. Everyone that has big bored a dirt bike will tell you it gives you more bottom end with little to nothing on top.

 

[JT78]

It's up to the individual I've run saws that could cut fast at a low rpm due to being able to throw some big chips but have had saws that cut just as fast with less pressure and higher rpms. I have a 55 rancher closed port that is stupid fast with some rpms and the rakers set right but have a 350 that was built more for torque that runs dead even with it at a lower rpm. All parts play into it just like with building a good 4 stroke engine I have a 302 that has less torque than my friends 347 but it's a lot faster than the 347 due to all the working parts being just right heads cam intake headers ect. Same with saws it's up to the chain how the ports are set up compression mixed with gearing of sprocket ect it all up to the operator some people like the bottom end torque others the top end rpms just depends on who is running it and the set up.