Part Two: The Intake Port

[moby x]

what do you have to say about it?

 

[Mastermind]

View attachment 170104 what do you have to say about it?

That's how I did a bunch of them.....

 

[thedude74]

Great read and very informative. Thanks to all for participating. Questions and answers were both helpful. On to part 3 (port 3?)......

 

[smokey7]

View attachment 170104 what do you have to say about it?

Did you poke those holes in the stratosphere runners? What model saw is that?

 

[moby x]

Jonsered cs 2253

 

[Ronie]

Can you compensate for a small carb by lowering the the intake floor. I just got a Husqvarna 51 and was looking at the walbro 170, it's tiny.

 

[Mastermind]

Can you compensate for a small carb by lowering the the intake floor. I just got a Husqvarna 51 and was looking at the walbro 170, it's tiny.

It's not so simple.

A longer intake duration doesn't really make up for a carb that's too small.

 

[Ronie]

It's not so simple.

A longer intake duration doesn't really make up for a carb that's too small.

Thanks

 

[JohnnyBlade]

Over a year and u brought it back @Ronie !
Sweet, ive read everyone of these theory threads multiple times. My question to @Mastermind is when porting i understand a degree wheel and hitting numbers but how is intake or exhaust duration measured? Ive tried to figure out myself how its measured but my info doesn't jive with others so i dont believe im doing it rite and or reading it wrong. Seemed like a great time for my question. Also how does one go about figuring out if a saw benefits with a shorter or longer duration over a factory duration?

 

[Mastermind]

Over a year and u brought it back @Ronie !
Sweet, ive read everyone of these theory threads multiple times. My question to @Mastermind is when porting i understand a degree wheel and hitting numbers but how is intake or exhaust duration measured? Ive tried to figure out myself how its measured but my info doesn't jive with others so i dont believe im doing it rite and or reading it wrong. Seemed like a great time for my question. Also how does one go about figuring out if a saw benefits with a shorter or longer duration over a factory duration?

To measure duration you're just seeing how many degrees of crankshaft rotation each port is open.

On these forums you will usually hear us talk about opening points. For instance...

Exhaust 102°
Transfers 122°
Intake 78°

This would be measured in degrees of crankshaft rotation from TDC.

As to how to know if a certain engine needs more or less duration on a port, trial and error coupled with experience is what that takes.

 

[JohnnyBlade]

To measure duration you're just seeing how many degrees of crankshaft rotation each port is open.

On these forums you will usually hear us talk about opening points. For instance...

Exhaust 102°
Transfers 122°
Intake 78°

This would be measured in degrees of crankshaft rotation from TDC.

As to how to know if a certain engine needs more or less duration on a port, trial and error coupled with experience is what that takes.

Ok so lets say intake is set at 78 *, from there duration is measured till the piston closes that port fully again? Or is duration from port cracking to fully open? Is intake duration measured from piston travel down to close or bdc to fully open?And i have dabbled it the trial and error its the Theory that im trying to wrap my brain around not just numbers. Thanks! Hope this makes sense, still unsure if i worded my questions right.

 

[Wonkydonkey]

It is measured from when a port cracks open till it closes. So if It cracks open at 78 you start to count from 78. Until it closes that’s the degrees of duration. If you want to make it more simple, set your wheel at 0* when the port opens carryon turning the wheel until the port closes. What ever the number is when it closes, that’s your duration. This way there’s no maths
When you get your head around it it’s very simple..

 

[Wonkydonkey]

I think I read your post wrong 78 would be when it normally closes

but if follow the rest of what I said if you set your wheel at 0* when the port opens etc...

 

[Ronie]

Does anyone know the math to convert degrees to duration. I use to know it and have now forgotten. I just remember that it simple like intake times two gives you the duration, or something like that.

 

[Ronie]

Is this right? 360-degree=A then A-degree=duration
For 100 degree
360-100=260
260-100=160 duration

 

[Nutball]

It's not so simple.

A longer intake duration doesn't really make up for a carb that's too small.

Does it at least help in your opinion?

 

[JohnnyBlade]

Is this right? 360-degree=A then A-degree=duration
For 100 degree
360-100=260
260-100=160 duration

See thats exactly what i was thinking. I just didnt know how to word it. That would be total tim of port opening.

 

[Ronie]

See thats exactly what i was thinking. I just didnt know how to word it. That would be total tim of port opening.

I'm not sure if that's the right way to do it.

 

[srcarr52]

It's not so simple.

A longer intake duration doesn't really make up for a carb that's too small.

IMO, longer intake duration just kills crankcase compress and makes for a lazy saw.

 

[JohnnyBlade]

I'm not sure if that's the right way to do it.

Me neither but thats how i am thinking. 2 people cant be both wrong Ronie. Plus its on the interwebs now so it has to be true