Husqvarna 350 mod questions

[sawlog1992]

So I read this about Husqvarna 350 modifications:

http://arboristsite.com/chainsaw/140617.htm

and saw this:
“The intake and exhaust were widened a lot. They're now at 70% of bore.”
What does that mean?

Also, down the thread:
“Good to know that there is a Meteor alternative to the Golf. So….do you plan on running a 359 carb on it?”
If I mounted a 359 carb on it, on a bare bones saw would it improve performance?

Thanks,

 

[4492011]

If you read further into the thread you will see that on that particular build he tried the zama carb of which did not work out the saw ended up with the standard carb back on in the end.

I dont beleive that just putting a larger carb on a stock 350 would help much. I do beleive that if it were ported it would help the performance a little.

 

[tolman_paul]

The 350 has a 44mm bore, so 70% of that is 30.8mm or 1.213" The big caution about going with a wide port is you run the risk of catching a ring and causing catastrophic ring failure. The other risk is that while the ring may not catch, you will have increased ring wear and cylinder wear. One way to alleviate this issue is instead of going with a flat top port roof the top of the port is slightly rounded to provide a more gradual transition for the ring.

A more conservative approach is to limit port width to 65% of bore, or in the case of the 350 26mm / 1.024"

 

[mweba]

Port size is often given more credit than deserved. Port timing and shape in most instances will produce more gains. If it were truely a matter of making the ports 70% and slapping on a larger carb....every saw would turn out fast.

 

[tolman_paul]

It's a combination of port width and timing, but if you look at the two strokes that are putting out the highest hp/cc they run 5 intake ports and 2 or three exhaust ports. The two port exhausts have the top of the port extended over the rear transfers, and the 3 port exhausts have two mini ports located on top of the rear transfers.

 

[mweba]

Um ya....this is a 350 owned by a virgin porter. Best to start simple.

 

[sawlog1992]

Um ya....this is a 350 owned by a virgin porter. Best to start simple.

I think I will start with one of my trash can string trimmers!

Where does timing come into play? I am guessing it has something to do with no valves (like a 4 cycle), and ASSuming that the port size will effect when the intake is sucked in and the exhaust is blown out. Is that right?

 

[tolman_paul]

Think of port timing on a two stroke as the same as cam timing on a 4 stroke, same principal and effect.

The height of the port affects at what rpm the engine will make it's power, higher port timing and the engine will run at higher rpm, however at the loss of low end power. More air/fuel in and more exhaust out equates to the ability to run at higher rpm, though the engine has physical limitations on how high it can rev w/o damage. Also the relationship between intake and exhaust timing is important.

I highly recomend getting a copy of A. Graham Bells two stroke tuning book for a proper understanding two stroke opperation and tuning, there is much more to the subject than can be addressed in a quick internet post.

 

[nstueve]

EDIT: looks like above post got there first while I was punching this out but I'll leave it incase it helps in any way...

I think I will start with one of my trash can string trimmers!

Where does timing come into play? I am guessing it has something to do with no valves (like a 4 cycle), and ASSuming that the port size will effect when the intake is sucked in and the exhaust is blown out. Is that right?

port timing is determined by when the cylinder passes over the particular port instead of when a cam will open and close a valve. Your "valve" is the cylinder essentially in a 2 cycle. Port timing is determined by when the piston passes the port windown and how long the piston allows the port to be open or closed...

Duration = the number of degrees in a 360* revolution of the crank that the particular port is open.

You can change port timing/duration by doing a number of things including shaving the base of the cylinder, shortening piston skirts, and of course getting the dremel (or similar) and grinding out the port windows to make it open quicker, or have more duration, etc...

I probably fumbeled something being short on sleep so someone correct me on the above if need be.

 

[4492011]

Some of the 350's have a 45 mm bore like the one in Brads thread. You can see some very good gains by removing the base gasket make sure you check the squish the base gaskets that I have measured are right at .020 you can check your current squish by removing the spark plug and put two pieces of solder that measures aprox 46 to 50 thousands bend them to the left and the right of the plug hole so that enough goes to the cylinder wall above the wrist pin leaving enough sticking out so that you can hold on to them and remove. turn the motor over by hand remove the solder pieces and measure them if they measure around .040 you can safely remove the base gasket and reasemble with some sort of gasket maker like permatex moto seal. and since you have the cylinder off you can widen the intake and exhaust port a little maintaining the same shape and making sure not to exceed the 65-70 % of bore diameter. These saws really run good just doing those couple of things including modifing the muffler.