The Great 2-stroke debate : Compression vs Flow

[Fabulous]

Compression or Flow ? Or a combo of both ?

 

[59billy]

Yes.

 

[Fabulous]

What’s the “golden ratio” ?

 

[59billy]

Hopefully, an actual smart person will reply, but in the meantime time, here's my take:

Empirically, we know that increasing compression with machining, BGD, or a popup piston can increase power.

Or, we can improve flow with muffler mods, matching exhaust port to muffler, polishing exhaust port, etc.

Which one gives the greater return? Probably depends on the saw. Different makers cut different corners. 90% of the mods we do to saws are things that maker could have done, but didn't, to cut costs.

 

[EFSM]

Most of us know what porting is like before we had access to a lathe. I think it can be good to learn without the option of raising compression, because it forces you to follow Randy’s motto: less is more. But the real freight trains come with increased compression.
Also remember that properly done porting can increase the dynamic compression without machine work.

 

[farminkarman]

definitely a combo of both for most saws. I would prioritize having effective quench with a tight squish clearance over some theoretical compression target. I have done too much machine work chasing compression to later find out that I ended up with too much intake or strato duration. Is there a particular saw you are considering?

 

[Agent Smith]

A bump in compression is good. I also go for flow and angles. Maybe im not too smart or skilled but in my porting endeavors, port shapes and angles have been quite important

 

[Fabulous]

Most of us know what porting is like before we had access to a lathe. I think it can be good to learn without the option of raising compression, because it forces you to follow Randy’s motto: less is more. But the real freight trains come with increased compression.
Also remember that properly done porting can increase the dynamic compression without machine work.

I think that is an important point : static vs dynamic compression. Static being measured when pulling the saw over vs the dynamic compression when the saw is cutting at 10000 rpm in the wood. It’s been my experience that too much compression may cause too much heat and then we are going backwards. There is no magic equation afaik - without testing equipment costing thousands if not tens of thousands of dollars it’s a game of little by little until you are satisfied with the performance.