Chainsaw Porting Theory

[Mastermind]

What we can't do is compare a strato engine to a non strato engine. The relatively small intake port on the strato can be misleading......the engine also draws in air through the strato ports. Although the transfers are stacked in layers, some mixing must occur, or the engine would never run as well as it does.

When I mod a strato engine, I rarely do anything to the intake side. I'm afraid of messing up the balance of fresh air VS mixed intake.

 

[Deets066]

What we can't do is compare a strato engine to a non strato engine. The relatively small intake port on the strato can be misleading......the engine also draws in air through the strato ports. Although the transfers are stacked in layers, some mixing must occur, or the engine would never run as well as it does.

When I mod a strato engine, I rarely do anything to the intake side. I'm afraid of messing up the balance of fresh air VS mixed intake.

Have you messed up a strato before by doin that?

 

[Mastermind]

Have you messed up a strato before by doin that?

No.......but I've fixed some that other people messed up.

 

[idiotwithasaw]

On the strato would there be any benefit from gutting the boot and filter horn and basically do away with the fresh air transfers. Where one transfer feeds directly from the intake would there even be enough vacuum to pull enough Mix up where you have essentially lowered the pressure in the boot?

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[merc_man]

What do you guys mean by strato saw?

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[Mastermind]

On the 241, and 261 Stihl there are big gains in gutting the jug and boot.

I can get the same gain, or more with port timing tweaks though.

 

[Mastermind]

What do you guys mean by strato saw?

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[merc_man]

Thank you. I appreciate ya getting the video for me.

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[Keith Gandy]

Gutted 241c

 

[exSW]

On the 241, and 261 Stihl there are big gains in gutting the jug and boot.

I can get the same gain, or more with port timing tweaks though.

Without losing the advantages of a strato. Does this go for the 6100 also?

 

[Mastermind]

The 6100 is a different design.........gutting it isn't really a possibility.

 

[David Young]

I think what you are doing with your tweaks Randy is making the charge in the true intake more fuel rich. Especially on the 661 where you shorten the intake duration.

We know the saw had to have the correct fuel air mix to run and we know where this fuel enters from.

If this concept was taken further it would've similar to fuel injection.

So the benefit in a two stroke motor is we are counting on the transfer cycle to flush the burnt charge and fill with Unburned charge. I think the mods you make are increasing the over scavenging. Which is the oem design for emission purposes.

By raising the transfers. You getting a more pure charge in the cylinder.

I think the mods you do work well whether you figured this all out or backed into it. Nice work.

Gutting the stratos is going backwards imo

 

[paragonbuilder]

In the pipe saw I just ported.....

EX: 85
TR: 120
IN:85

The pipe sends a wave of pressure back into the exhaust port........so the transfers stay closed for 35° after the exhaust opens.

I'm thinking on Al's muffler idea, timing number will need to be different for it to work.

This is interesting because it proves that changing one thing and testing to find out you lost power doesn't mean it was bad. It just means something else also may need to change to see the gains. It's like a symphony. It all intertwines, which is what makes this all so puzzling and interesting. Seems like all these rules we are seeking aren't really there. Trial and error is where it's at. In fact I think Blair and Bell both said that you can get close with "rules", but the rest is try it and see...

 

[Mastermind]

This is interesting because it proves that changing one thing and testing to find out you lost power doesn't mean it was bad. It just means something else also may need to change to see the gains. It's like a symphony. It all intertwines, which is what makes this all so puzzling and interesting. Seems like all these rules we are seeking aren't really there. Trial and error is where it's at. In fact I think Blair and Bell both said that you can get close with "rules", but the rest is try it and see...

We have traveled a long and winding path, and finally we have reached our destination......

There are no set rules, no absolutes.

We get close with experience, whether ours or someone elses. Then we test, and tweak, and test some more. We hone in on what works well for us, on each model. Then.....we second guess ourselves, and we try new ideas.

That is the joy of these infernal two stroke machines.....figuring them out is so challenging.

 

[drf256]

We have traveled a long and winding path, and finally we have reached our destination......

There are no set rules, no absolutes.

We get close with experience, whether ours or someone elses. Then we test, and tweak, and test some more. We hone in on what works well for us, on each model. Then.....we second guess ourselves, and we try new ideas.

That is the joy of these infernal two stroke machines.....figuring them out is so challenging.

Gospel

 

[jmssaws]

Anyone running full circle cranks?

What about timing with a full circle?

I got one coming for my 066 is also have a cylinder I can port just for it if I need too.

How bout it guys,teach me about them

 

[mdavlee]

You'll have more velocity in the transfers. Won't have the same volume in the case so opening the lowers may be required to get enough room for a full charge. Power band is usually higher up as well.

 

[drf256]

How was the crank made J?

 

[jmssaws]

Thanks mike,I thought with so much volume gone I could open the transfers and intake bigger, 288 piston also.

Definitely new territory for me.

 

[jmssaws]

How was the crank made J?

I don't know enough about it to explain how. @awol can explain