Part Two: The Intake Port

[XP_Slinger]

2 Stihl 046/460

This one has around 20% more port area than the second.

Unfinished

View attachment 68535

Finished

View attachment 68536

Smaller port with rounder edges

View attachment 68537

Guess which one makes the same WOT rpm free spooling and more rpm in the cut? Which one losses the least rpm when you dawg it in and pull up on the handle hard?

My guess is the smaller one.

 

[Moparmyway]

The theory behind that is because the intake is going from a greater pressure,atmosphere to a lesser pressure,crankcase that this creates a cooling effect .This in turn would have a tendency to cause the fuel /air mixture to condensate on the walls of a mirror smooth intake track as opposed to a vapor like mixture .

Except that the drop in pressure will cause any liquid to flash off easier

Finally found a use for Save Edge

I've gotten some new ones that wouldnt wittle a wet noodle in a day of tryin

 

[Stump Shot]

So would you fellas think that for a firewood saw that the intake port is the least to worry about of the three? Or would that be a gross miscalculation on my part?

 

[drf256]

My guess is the smaller one.

Exactly.

Air flow dynamics play a roll here. The intake port flows from vacuum and not pressure. Make it too big and you'll lose vacuum and the midrange of the saw will suck. The top end may be better with a bigger port.

As the piston rises and the case creates negative pressure the port starts to flow. Make the intake too large and it has an effect like making the case larger in some respects. The vacuum and flow that's created isn't perfectly linear.

Hope I'm explaining my thoughts correctly. Then again, doubt too many care.

 

[XP_Slinger]

Exactly.

Air flow dynamics play a roll here. The intake port flows from vacuum and not pressure. Make it too big and you'll lose vacuum and the midrange of the saw will suck. The top end may be better with a bigger port.

As the piston rises and the case creates negative pressure the port starts to flow. Make the intake too large and it has an effect like making the case larger in some respects. The vacuum and flow that's created isn't perfectly linear.

Hope I'm explaining my thought correctly. Then again, doubt too many care.

Great info. You nicely illustrated how bigger isn't always better for a work saw. You've put a big question in my head to rest. That's what this series of threads is all about! Thanks Doc.

 

[drf256]

Great info. You nicely illustrated how bigger isn't always better for a work saw. You've put a big question in my head to rest. That's what this series of threads is all about! Thanks Doc.

I have limited real world experience. Many of the guys here have tons more. I try to pay attention to what the big dogs here have said and incorporate into what I do.

Take my opinion with a grain of salt. It's worth what you just paid for it.

 

[Moparmyway]

Exactly.

Air flow dynamics play a roll here. The intake port flows from vacuum and not pressure. Make it too big and you'll lose vacuum and the midrange of the saw will suck. The top end may be better with a bigger port.

As the piston rises and the case creates negative pressure the port starts to flow. Make the intake too large and it has an effect like making the case larger in some respects. The vacuum and flow that's created isn't perfectly linear.

^^^^^^^^^^^^
THIS !!!!

1. Hope I'm explaining my thoughts correctly.
2. Then again, doubt too many care.

1. Perfectly Doc !!
2. You couldn't be more wrong if you were paid to be

 

[Stump Shot]

Exactly.

Air flow dynamics play a roll here. The intake port flows from vacuum and not pressure. Make it too big and you'll lose vacuum and the midrange of the saw will suck. The top end may be better with a bigger port.

As the piston rises and the case creates negative pressure the port starts to flow. Make the intake too large and it has an effect like making the case larger in some respects. The vacuum and flow that's created isn't perfectly linear.

Hope I'm explaining my thoughts correctly. Then again, doubt too many care.

Your grasp of the subject and wonderful explanations of same are just absolutely excellent. Thanks.

 

[Deets066]

Well put Doc

 

[Deets066]

How bout finish?

I like to hit with 100 grit emery on a split mandrel and then bead blasted

 

[drf256]

How bout finish?

I like to hit with 100 grit emery on a split mandrel and then bead blasted

You have the nicest port finish I've ever seen Deeter.

I don't have an answer. I try to keep my intake ports not too shiny.

 

[Simondo]

Yes....and yes. Yes, that too.



The reeds are just on the strato ports.

If memory serves me.....you "Contaminated " ! ...that on the 6100 reed valve stratto feed ?

 

[Deets066]

Thanks ol' buddy

 

[mdavlee]

I like burr finish in the intake

 

[drf256]

A lot less work Uncle Mike.

 

[Deets066]

A lot less work Uncle Mike.

Not really, I spend maybe 1-2 minuites with a split mandrel and 15 seconds in the bead blaster

 

[Deets066]

Grinding and setting height is what takes time

 

[mdavlee]

A lot less work Uncle Mike.

I haven't found a difference in power. It just isn't as pretty. A few of my saws have burr finish everywhere.

 

[XP_Slinger]

How bout finish?

I like to hit with 100 grit emery on a split mandrel and then bead blasted

I like that idea. I've always stippled it with a double cut bit, just kinda letting the dremel bounce around with light pressure. I'll be plagiarizing your method on the next one I do. Gladly pay a royalty...lol

 

[Stump Shot]

What are you fellas doing with intakes like the 272 and 288 series cylinder ports with the odd shaped port for mounting screws?