Spuds Porting and Tuning Thread

[Stubby]

Hi Steve have you ever ported an Irish motorbike aka a cut off saw ? Quite fancy a. Pokey husky 760 ?

 

Think cut off saws have a limiting coil , more so than some saws , so the disk cutter can not spin above the printed max revs on the label . Thats why when they are revving in fresh air they misfire .

[twistedhicap]

Think cut off saws have a limiting coil , more so than some saws , so the disk cutter can not spin above the printed max revs on the label . Thats why when they are revving in fresh air they misfire .

 

 

That is a good point but that aside would it gain more useable power in the cut maybe ?

[adw]

As Stubby says they are goverened to 10.000 rpm to protect the wheel, the coil from a 372xp would fit, but you will well exceed the 4.7 spindel speed, on your own head be it, to be honest the K760 already has plenty of power, you would gain more power than the cutting wheel could take, a diamond wheel would probably glaze and over heat,, my advise do not do it!!

[twistedhicap]

As Stubby says they are goverened to 10.000 rpm to protect the wheel, the coil from a 372xp would fit, but you will well exceed the 4.7 spindel speed, on your own head be it, to be honest the K760 already has plenty of power, you would gain more power than the cutting wheel could take, a diamond wheel would probably glaze and over heat,, my advise do not do it!!

 

 

Fair comments taken on board and settled I'll just leave spud to fettle my saws instead

[peatff]

I've never used a cut off saw and thought "this ought to be making more noise and dust, I'll see what I can do" The 12" discs are only rated to about 6000rpm as well so not really a fruitful exercise making the saw outpace them.

[twistedhicap]

I've never used a cut off saw and thought "this ought to be making more noise and dust, I'll see what I can do" The 12" discs are only rated to about 6000rpm as well so not really a fruitful exercise making the saw outpace them.

 

 

Wasn't thinking about overspeeding the disc but thinking more about torque and keeping the speed up in the cut as in some cuts the saws can run out of go that's all I was thinking

[openspaceman]

Think cut off saws have a limiting coil , more so than some saws , so the disk cutter can not spin above the printed max revs on the label . Thats why when they are revving in fresh air they misfire .

 

Good point.

 

Also the reason stihl drills and hedge cutters that have an ignition rev limiter foul their exhausts with tarry unburned fuel if people insist on holding the throttle open all the time.

[spudulike]

Ment to put that i bace the ratio around 100 mm and the Golden section of that would be 62 mm or a 1/3- 2/3rd APROX kinda deal. Hope that makes sense

 

Having a rule of thumb is ok but you can't just open up ports as some have limitations such as skirt size and ring ends plus there is a known two stroke tuning rule on port size and I personally stick to this rule as it has seen me well!

 

I don't get too hung up on the exhaust outlet to exhaust port size, you are just increasing flow and trying not to make the saw stupidly noisy!

 

Looks like the cut off saw has run to conclusion! Personally I find chainsaws nicer to use!

[peatff]

Ment to put that i bace the ratio around 100 mm and the Golden section of that would be 62 mm or a 1/3- 2/3rd APROX kinda deal. Hope that makes sense

 

The golden ratio is only something about what works in nature or is pleasing to the eye not what is efficient in mechanics.

[Sawchip]

Having a rule of thumb is ok but you can't just open up ports as some have limitations such as skirt size and ring ends plus there is a known two stroke tuning rule on port size and I personally stick to this rule as it has seen me well!

 

I don't get too hung up on the exhaust outlet to exhaust port size, you are just increasing flow and trying not to make the saw stupidly noisy!

 

Looks like the cut off saw has run to conclusion! Personally I find chainsaws nicer to use!

Point taken on the limitations of piston/ring and placement /geometry of the cylinder as you find it from the manufacturer.

Im sure you have a tried and tested tuning rule, plus the art of cylinder work is far from a simple 1 sentence description as to how and what to do. Do you feel that the final outlet on the muffler has to have a ratio in a certain region to give the best results with your port work so as not to still restrict to much.

Would it all be for nowt if the outflow wasn't enough ?

This 70-80% rule of thumb seems to crop up a lot.