Closed or open port

[wyk]

A boost port is usually diametrically opposed to the exhaust. Extra transfers simply give the engineer more opportunities to tailor how and when the ports flow. Like with any two stroke motor, it is very important how the exhaust and the intake charge flow and react to and with each other. With chainsaws, it's very important to fill up the chamber as much as possible with an incoming charge, which pushes out the left over gases, yet doesn't start to shove some of it's own intake charge out that same exhaust port. It's not possible to avoid it, really, unless the saw is running very lean and has a lot of back pressure from the muffler(as with most modern factory saws nowadays). The best way to tune a two stroke engine is with a tuned exhaust pipe - but these tend to get in the way if the machine is used to sawing.

 

 

 

How a pipe helps retain the incoming fuel charge:

 

[ame=http://www.youtube.com/watch?v=s_BGFb13Obg]Animation - How two stroke engine works. ? - YouTube[/ame]

Edited February 18, 2014 by wyk

[spudulike]

I always love the silence you get after explaining something that gets a little technical - think "glazed eyes" comes to mind:001_rolleyes:

[wyk]

I always love the silence you get after explaining something that gets a little technical - think "glazed eyes" comes to mind:001_rolleyes:

 

Eh... I made all that up. Saws are witchcraft.

[spudulike]

Eh... I made all that up. Saws are witchcraft.

 

Ah...thats better, something we can all understand:lol:

 

It's a bit like the bloke that lifts the car bonnet and looks at the engine like he may magically find the answer to why his engine won't start in the engine bay:lol:

 

I think most guys wish they hadn't asked once I get in to full flow:blushing:

[wyk]

Ah...thats better, something we can all understand:lol:

 

It's a bit like the bloke that lifts the car bonnet and looks at the engine like he may magically find the answer to why his engine won't start in the engine bay:lol:

 

I think most guys wish they hadn't asked once I get in to full flow:blushing:

 

I imagine many women are also afraid of said flow.

[Andy4D]

How do such additional ports work?[/quote

 

Boost ports are normally opposite the exhaust port and are aimed upwards in order to swirl the charge (from the transfer ports) up towards the combustion chamber. This helps push out exhaust gases out of the cylinder without blowing too much fresh mix out the exhaust.

The extra ports Wky shows are usually a combination of boost and transfer port - they help direct the fresh charge up (and back) to maximise exhaust gas removal, and reduce transfer speed to minimise charge loss out of the exhaust.

[Macpherson]

smashing wee cartoon, aren`t the principles so simple !!

When I was 14 I got " sook, sqeeze, bang, blaw" drilled into me,....if you could just get a 4 stroke to work upside down !!

[urbandekay]

Wyk, so I am still a little confused; here, "You could also add fingers ports that act as both transfers and boost ports." you seem to be implying that a boost port is not a transfer port, yet above you seem to say that a boost port is an additional transfer port. Also, what are finger ports, which you denote as different to either?

[urbandekay]

smashing wee cartoon, aren`t the principles so simple !!

When I was 14 I got " sook, sqeeze, bang, blaw" drilled into me,....if you could just get a 4 stroke to work upside down !!

 

 

You could have a 4 stroke that worked upside down by providing it with an efficient oil scavenge pump and a dry sump, with separate oil tank. But power to weight ratio would be bad

[Stubby]

You could have a 4 stroke that worked upside down by providing it with an efficient oil scavenge pump and a dry sump, with separate oil tank. But power to weight ratio would be bad

 

Small air craft engine ? ( fully aerobatic )