Let's Talk Transfers

[XP_Slinger]

It takes a lot of heat to ignite with out spark.


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I think a diesel chainsaw would be interesting...lol

 

[Deets066]

Saws can diesel a little when they are run hard when it's hot and they have s lot of compression

 

[jmssaws]

Saws can diesel a little when they are run hard when it's hot and they have s lot of compression

I've had it happen once.

 

[Deets066]

Scott..... I believe I know less after reading thread! Your makin muh head hurt

 

[Deets066]

So what's the concensus on ex side fingers in a two port?

 

[paragonbuilder]

So what's the concensus on ex side fingers in a two port?

Try it!


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[drf256]

Tighter cases with less intake duration can tolerate lower transfers, and vica versa. Trying to fill chamber fully without pushing any out of the exhaust.

Higher exhaust duration needs less transfer duration or it will vent fuel too fast.

I still don't see how fingers should open last, but many newer designs seem to open the exhaust first.

This is what I see so far.

 

[spencerpaving]

Mains open first directing charge across the piston towards the intake side....then boost port opens helping the charge up the backside of cyl towards the head also helping exhaust out....hence loop scavenged...

 

[wigglesworth]

Transfers are easy....

Just start raising em, and when they start spitting raw fuel out the muffler, there just about right...

 

[Mastermind]

Even with the exhaust port....

 

[drf256]

Ahhh...I see (said the blind man)

 

[tree monkey]

So what's the concensus on ex side fingers in a two port?

andy dodgegeeks 346 I did for him has them

Mains open first directing charge across the piston towards the intake side....then boost port opens helping the charge up the backside of cyl towards the head also helping exhaust out....hence loop scavenged...

you are correct sir

 

[drf256]

Ok.

So we are blowing off the piston, then pushing the charge towards the intake wall, then pushing it upwards.

But....

How is a finger pushing it up?

And with the cross sectional area of one, I postulate, that they may flow less. So even if they open earlier, could their effect be coming later?

 

[tree monkey]

you don't want the fresh charge mixing with the spent charge.
if the boost ports or secondary's open first it is more likely to mix.

 

[Deets066]

you don't want the fresh charge mixing with the spent charge.
if the boost ports or secondary's open first it is more likely to mix.

Never looked at it like that before, so by coming straight across the piston and then up your giving the ex time to discharge

 

[tree monkey]

the more pure the charge is the more power you get from it.
the more charge you can keep in the cylinder the more power you get.
fuel out the muffler is wasted

 

[Stihlbro]

Transfers duty in the cycle of a two stroke simply flush out burnt gas and recharge combustion chamber with fresh charge. The multitude of shapes, opening points, transjectory angles are serving the same purpose. The difference comes from crankcase volumes. There are gains to be had with modifying correctly. The ultimate goal is cylinder fill. Boost ports,auxiliary ports, fingers ,ct13's(lol), what ever you call them, are secondary transfers that are done to aid in cylinder fill. The more uncontaminated charge in the combustion chamber the more power you make.
Each saw is different, depending on what you are building for, entry angles/depth/width and proper placement is what makes them effective. Main thing is you are not trying to run a saw off auxiliary transfers, your filling void of cylinder fill.

Most new strato designs are using fresh air to purge spent gas from chamber before transfers recharge with fresh charge. The concept can be the same with booster ports at the expense of fresh charge out the exhaust. Delaying boost ports can aid in less out the exhaust and better cylinder fill. Better cylinder fill=more power.

So the long and short of my interpretation, if auxiliary boost ports are found effective, what are you leaving on the table with factory transfers. Is it time area, opening points, roof angle, transjectory angle?

 

[Deets066]

So why not open the fingers/ boost ports at the same time with flat entry angles and just let the piston force the charge up? That would give the exhaust the most time to do its own thing without using the fresh charge to do the work

 

[Stihlbro]

You do what ever it takes to get the best cylinder fill. This is figured out with testing. 2 port or 4 port transfer motor?

 

[Deets066]

You do what ever it takes to get the best cylinder fill. This is figured out with testing. 2 port or 4 port transfer motor?

2 port