Chainsaw Porting Theory

[merc_man]

Finding port height.

So when you figure out your port hight. Do you take a stock readng before tou deck or gasket delete.

How do you know how much to take off the roof of port if ya wanna change timing. Is it so many degreese you can go for a max?

 

[Deets066]

So when you figure out your port hight. Do you take a stock readng before tou deck or gasket delete.

How do you know how much to take off the roof of port if ya wanna change timing. Is it so many degreese you can go for a max?

It's different for every saw, and some people like the same saw ported different ways for how they are to be used.

Porting is an art that takes a while to get good at

 

[drf256]

View attachment 15066

They just look cool

So do you think the grinding inside the transfer tunnel has anything to do to with why it runs so well?

 

[drf256]

I already raised to 94 just haven't ran it yet.

I believe I have another problem, I put another known well running cylinder on it and got the same results, no rpm and no 4stroke at 13500 even. I changed carbs but still the same. Wtf would cause it to run out of fuel? I'm going to drill the jet but I've never had to before.

Ignition?

Interesting J.

Explains the head scratching about your initial numbers, which seemed just fine.

Without a pipe, I'd be interested to see how 93 ran.

 

[drf256]

On a stihl 78 is my favorite intake number and 118 is my favorite transfer number but the exhaust has me thinking lately,I don't believe it needs to be as low as most including me think.

I've been cutting 050 or 060 from the chamber still but instead of leaving it 101-103 I'm raising to 98 and there gaining from it. Instead of 240 there 215-220 but it's not the compression loss making the gain it's blow down, I'm sure your thinking well why not leave the transfers at say 123 and gain blow down but it won't work I've tried.

One number effects the other numbers,I like one set of numbers but everything else determines where everything else needs to be. You dig?

Sounds like a popup piston attempt may be in order. What's the stock exhaust J, 98?

You'll need less transfer work for sure that way. Have you tried a popup J? I'm sure you have.

I could see a mere 200psi popup saw working quite well here. Would be interesting to see the difference.

 

[drf256]

J,

Why do you think your 394 runs so much better than your 066?

What's different about the jug? Are the ports just bigger? One central pinned ring?

Any pics of a 394 jug?

 

[paragonbuilder]

J,

Why do you think your 394 runs so much better than your 066?

What's different about the jug? Are the ports just bigger? One central pinned ring?

Any pics of a 394 jug?

Cuz it's a husky! [emoji23]
It is interesting. Very similar cylinders. Be nice to compare side by side. Are the strokes the same? Case volumes?


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[Mastermind]

I used pop-up pistons for a long while. It was my customers that pushed me into using cut squish bands. Once I got used to cutting the squish band, the pop-ups seemed like more trouble. I've built some very strong runners with a popup, and I can see where they actually make more sense in some cases.

The flat top seems like it would be more resistant to detonation though....

 

[jmssaws]

I have a 660 that is half popup half squish band cut and it runs fine.

The best exhaust I've seen on a 660/066 cylinder is 97,the best transfers I've seen are 120 but there usually much lower so a popup can't get me where I want to be.

Now a 460 on the other hand I believe works better with a popup.

 

[jmssaws]

J,

Why do you think your 394 runs so much better than your 066?

What's different about the jug? Are the ports just bigger? One central pinned ring?

Any pics of a 394 jug?

The 94 has more compression and a 56mm bore,there's not much room for widening anything and the 2 saws have almost identical numbers. I really don't know why, stroke x bore maybe makes the difference or the huge muffler.

I've never ran a saw that will rev with the 94,my 95 wont.

 

[jmssaws]

 

[jmssaws]

The 94 has a rm work chain and my red light has square filed 404 so that is why it's as close,if the chains were switched the 94 will clobber my beloved stihl.
Damn communist husky.

 

[Keith Gandy]

The 94 has a rm work chain and my red light has square filed 404 so that is why it's as close,if the chains were switched the 94 will clobber my beloved stihl.
Damn communist husky.

I love stihl 404 skip 28" on my MMWS 390xp. Feeds really well

 

[Keith Gandy]

Both thoso saws r cuttin really well Jason

 

[jmssaws]

It's 404 full comp that kevin sent me. @Moparmyway

The 94 has a round filed semi chisel work chain nothing special.

The 66 is tuned at 14200 and the 94 is 13500.

I noticed the idle screw is gone on my 94 so I checked my 95 and it's gone too. Lol
Damn husky

 

[huskihl]

It's 404 full comp that kevin sent me. @Moparmyway

The 94 has a round filed semi chisel work chain nothing special.

The 66 is tuned at 14200 and the 94 is 13500.

I noticed the idle screw is gone on my 94 so I checked my 95 and it's gone too. Lol
Damn husky

Before I sent the 7900 to TM, it wouldn't hold tune or idle. All 3 screws were working their way out on every piss rev. Stretched out both springs and blue loc-tited all 3. Good to go now....for awhile

 

[Iron.and.bark]

Great reading fella's added a lot to my meagre porting knowledge.

Being just a backyard grinder with a love of dolmars, I have essentially just made the intake & exhaust wider, reduced the base gasket thickness (big ass red bull cans & copper spray). Being in oz have to deal with some hard as wood, so prefer torque of these saws.

Come across a little doozy of a problem (well self inflicted). May have seen a question I posted on the other site re a 166 dolmar cylinder a month or so back.

Cylinder is toast so I am getting it replated, I am also considering getting it overbored to 58mm (still waiting on 58mm piston to arrive).

Should I keep the transfers as they are (as overbore will make the transfers smaller as a percentage of cylinder wall area)? Use will be milling so I want the maximum possible torque not a screamer

Hope I haven't taken the thread to off topic.

 

[paragonbuilder]

Great question! I think what you're trying to do is the very reason why a lot of the aftermarket big bore kit don't gain any power. Not only is the transfer entrance smaller but the entire tunnel is smaller so getting the volume you need into the cylinder is an issue. Also it seems when guys make hybrids they don't have the torque of their larger saw counterparts, possibly because of smaller case volume, but these are just my theories, and Dolmars seem to go by a different set of rules anyways. I'm interested in how you make out.


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[Redfin]

Interesting J.

Explains the head scratching about your initial numbers, which seemed just fine.

Without a pipe, I'd be interested to see how 93 ran.

Ive got a 66 with almost identical numbers ive been messin with. Its 95 and .05 wide from the skirt. Need to test it. It may hit 93.

 

[Mastermind]

Great reading fella's added a lot to my meagre porting knowledge.

Being just a backyard grinder with a love of dolmars, I have essentially just made the intake & exhaust wider, reduced the base gasket thickness (big ass red bull cans & copper spray). Being in oz have to deal with some hard as wood, so prefer torque of these saws.

Come across a little doozy of a problem (well self inflicted). May have seen a question I posted on the other site re a 166 dolmar cylinder a month or so back.

Cylinder is toast so I am getting it replated, I am also considering getting it overbored to 58mm (still waiting on 58mm piston to arrive).

Should I keep the transfers as they are (as overbore will make the transfers smaller as a percentage of cylinder wall area)? Use will be milling so I want the maximum possible torque not a screamer

Hope I haven't taken the thread to off topic.

Welcome to OPE.

Good topic for discussion in my mind.

I really don't have much to add, but I am interested in seeing where this goes.