First time porting

[merc_man]

I tried filing the flywheel key to advance timing. Tried saw and seemed to be stronger.

 

[merc_man]

Also put the compresion tester on and gained almoat 20psi.

 

[merc_man]

I was out looking at a parts 353 i got and was looking at the piston go up and down. I noticed on the saw i tried porting that the piston didnt quite clear the bottom of the exhaust port when at bottom dead center. The parts one with stock top end at bottom dead center clear bottom of port. Just wondering if the top end is so cheap and ports not to speck and mabe thats why i never had much for gains.

 

[mdavlee]

A lot of them don't go below the bottom of the exhaust port or transfer ports. Some shops were grinding the piston down at the transfers and exhaust to change the timing. I always wanted to try it to see how it would do since flow would be different there instead of hitting a straight edge like the transfers do.

 

[merc_man]

No.

Exhaust roof does three things. It determines when compression of charge begins, it determines the amount of trapped volume, and it determines when combustion pressure is vented.

There are some general rules on this. In my mind you want it to open at the very point where pressure from combustion becomes close to parasitic drag losses. That's the theory at least. The actual amount that's best for any individual saw varies because of design and stroke.

A lot of guys use a rule of thumb of exhaust opening based on displacement for a worksaw. 105 on 50cc, 103 on 60cc, 101 on anything larger. But no one fits all in this game. If you have too much compression, somethings you want a higher roof. If you want more rpm and less lugging power, sometimes you want a higher roof. Etc...

The more you learn in this game, the more confusing it becomes. I hope the above helps.

When you guys are getting ready to port a saw. Do you bother checking port opening degree and stuff or wait till you deck or gasket delete to check?

 

[huskihl]

When you guys are getting ready to port a saw. Do you bother checking port opening degree and stuff or wait till you deck or gasket delete to check?

I always degree them first if the model is known to have slight variances, like an 044 or 066, or if it's new to me

 

[jmssaws]

A 066 is a very random saw indeed.

 

[merc_man]

A 066 is a very random saw indeed.

are the cylinders all a bit different on 066?

 

[jmssaws]

are the cylinders all a bit different on 066?

They are all over with timing.

 

[merc_man]

They are all over with timing.

Sounds like it could be confusing.

 

[merc_man]

So even a new 066 saw stock wouldnt run the same as the next one then?

 

[jmssaws]

So even a new 066 saw stock wouldnt run the same as the next one then?

There would definitely be some that run better than others.

 

[merc_man]

So was just wondering. Has anyone figured out a percentage of gain by porting one step at time.

Like percentage of gain for muf mod
Percentage of gain for exhaust port widening, transfer work, intake And so on.
Just curious what each will gain.

 

[drf256]

When you guys are getting ready to port a saw. Do you bother checking port opening degree and stuff or wait till you deck or gasket delete to check?

I used to on all. Still do on some.

While there are variations, most stock timings have already been posted, somewhere.

Even if variation exists, there is usually an intended goal for numbers that is not dependent on the stock numbers anyway.

 

[Al Smith]

It can be debatable concerning exhaust port opening .I suppose it boils down to individual likes or dislikes .

Take for example the the o38 series Stihls,Mag and AV model .Stock they are 101 degree opening .I have two that open at around 96-97 and they have all kinds of power plus a tad more speed .The Mag will run nearly heads up in big wood with a stock Ms 660 and has D handle because of the compression .

FWIW in stock trim the 10 series McCullochs were set at 96 and for as old as they are they have plenty of torque .It's all about what the rest of the engine parameters are in addition to the exhaust port opening .

Now I'm not saying every saw engine responds the same .Just remember it's real easy to carve away aluminum buts it's a beech trying to put it back on .

 

[Fairways_and_Greens]

Very cool. What are you using for grinding?

 

[Mastermind]

Very cool. What are you using for grinding?

Hello, and welcome to OPE forum.

 

[Fairways_and_Greens]

Hello, and welcome to OPE forum.

Wow, a personal greeting from the Master. You do good work sir, and thanks for sharing!

 

[Mastermind]

Wow, a personal greeting from the Master. You do good work sir, and thanks for sharing!

Lots of guys here do good work. We strive to encourage unity and sharing of information on OPE. Since this site has been started, I've learned a bunch from guys that I'd never seen post before. It seems that there are a lot of ways to skin a cat. lol

Enjoy the site, and dig in. If you need help with anything saw related, you come to the right place.

 

[jacob j.]

A lot of them don't go below the bottom of the exhaust port or transfer ports. Some shops were grinding the piston down at the transfers and exhaust to change the timing. I always wanted to try it to see how it would do since flow would be different there instead of hitting a straight edge like the transfers do.

I never had good luck with that. I like to keep the top of the piston flat anymore, even if I'm lowering the crown. Cutting the edges of the crown for additional timing seems to make a "sloppy" motor to me, if that makes any sense.