Chainsaw Porting Theory

[drf256]

Exactly.



I've seen some horrible looking gouged out transfer ports in engines that run like hell. No thought at all but into the angles.....and the heights all over the place.

Sometimes I wonder why I try so hard......

When you start thinking of the motor dynamically, more than as one combustion cycle at a time, transfer angles begin to seem more important.

 

[drf256]

Which one creates what kind of power I have no idea...


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I think the answer is the one that creates the largest transfer area that purges the cylinder the best.

This is where the confusion lies.

Where is the dead space? How do we fill it most effectively?

 

[Keith Gandy]

I'm particularly interested in the upper entry pockets.

The higher one takes a transfer over stock, the more the entry angle is going to change over what the factory gave us.

There's an old diagram, I'm sure Jeremy @Adirondackstihl has it, that shows 90* vs. angled entry transfers. IIRC, the closer to 90* you get, the peakier but more powerful you get.

The factory quad setups seem to favor a 90* entry in the mains/exhaust side port that opens before the secondaries. So they angle the transfer tunnel towards the intake, but they open it squarely across the piston crown on the exhaust side first.

So has anyone experimented with different pocket entry angles?

I think Mdavlee has

 

[jmssaws]

I think the answer is the one that creates the largest transfer area that purges the cylinder the best.

This is where the confusion lies.

Where is the dead space? How do we fill it most effectively?

Turbo charger

 

[Keith Gandy]

Turbo charger

Needs nitro!!!

 

[Keith Gandy]

I think the answer is the one that creates the largest transfer area that purges the cylinder the best.

This is where the confusion lies.

Where is the dead space? How do we fill it most effectively?

Im thinkin a balance of velocity between the transfers and exhaust. Both tuned proportionally between different models of saws

 

[Keith Gandy]

Too much transfer, exhaust, and blowdown would kill a saw?

 

[Stihlbro]

Transfers are the "Napoleon dynamite" of chainsaw porting. When you think you got them figured-out, they do totally different. As Mastermind said in regards to entry angles, I've witnessed it as well. As Wigglesworth stated opening points, I've seen that too. I don t understand it but it works!! And that goes against all the talk on any reading material available. I'll end this post with this, I think there is too much jibberish on timing numbers than actual testing of porting. But please continue the discussion.

 

[Mastermind]

I love Neapolitan......

 

[Stihlbro]

 

[mdavlee]

I'm particularly interested in the upper entry pockets.

The higher one takes a transfer over stock, the more the entry angle is going to change over what the factory gave us.

There's an old diagram, I'm sure Jeremy @Adirondackstihl has it, that shows 90* vs. angled entry transfers. IIRC, the closer to 90* you get, the peakier but more powerful you get.

The factory quad setups seem to favor a 90* entry in the mains/exhaust side port that opens before the secondaries. So they angle the transfer tunnel towards the intake, but they open it squarely across the piston crown on the exhaust side first.

So has anyone experimented with different pocket entry angles?

You don't want it totally flat deep in the transfer if you can help it. That creates a dead space for flow.

 

[jmssaws]

I only raise the edge of the transfers and leave a upwards slope so to speak.

 

[Keith Gandy]

I only raise the edge of the transfers and leave a upwards slope so to speak.

I was goin flat all the way back but since have started doin the same with a slope

 

[Keith Gandy]

In my mind flat would cause the charge to collide with the flat surface and would disrupt the natural flow in

 

[beaglebriar]

I love Neapolitan......

Now I want ice cream.... Thanks Mr. Fitswell

 

[czar800]

Its raining today and I've had too much time to think so bear with me as I think through this.
I've read that transfer pressure is low like 10psi or less? Why not try and gain more pressure...by filling stuffing the uppers with JB and shaping it all towards the intake more like a nozzle shape?
In my limit understanding a few psi could increase velocity or just and a turbo!!!

 

[jmssaws]

Its raining today and I've had too much time to think so bear with me as I think through this.
I've read that transfer pressure is low like 10psi or less? Why not try and gain more pressure...by filling stuffing the uppers with JB and shaping it all towards the intake more like a nozzle shape?
In my limit understanding a few psi could increase velocity or just and a turbo!!!

Circle crank.

 

[czar800]

Circle crank.

There has to be another way.... I can't make a circle crank in my basement!

 

[Danders]

Circle crank.

Yep. The saw manufacturers have done a pretty good job though of minimizing case volume compared to what I remember from my early 70's dirt bike crankcases. Which isn't to say it can't be improved upon.

I wonder if part of the complexity of figuring out why different transfers can achieve good results is the interaction with the exhaust port. The engine is inhaling and exhaling at the same time, we try to quantify that with transfer timing and blowdown but we're missing something to explain why 2 saws with the same numbers run differently.

 

[paragonbuilder]

There has to be another way.... I CAN'T make a circle crank in my basement!

That word does not belong on this site!


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