A Tale of Three Saws

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AUSSIE1 said:
Increasing the midrange should increase the speed at which it cuts cookies due to being able to lean on the saw more and/or have more aggressive chain specs.
Some saws don't sound like they are working any quicker than a stocker, but are cutting quicker.
Click to expand...
A peaky power band may be able to cut just as fast, but only if the operator works hard to keep the saw in its narrow powerband. My old lame 066 BB was like that. It is not missed.

Real high (200 psi) cold cranking compression means nothing more than you have a good ring seal, or a smallish combustion chamber.
Click to expand...
:agree2: Yeah, and who wants a good ring seal or a smallish combustion chamber ? :) If that's what I wanted, I'd buy a Dolmar or a Solo, not a new Stihl 660. :chainsaw:

I guess the new popular mod on AS will be installing thicker base gaskets to reduce compression and heat, and then running the detuned saw on top of a mountain where the air is thinner, because compression is a really bad thing. :confused: Let's see those thick base gasket mods, with before and after cut times ! ! ! :hmm3grin2orange:

Brad, you must be a good photographer, because your closeups of the ports are awesome. Keep 'em coming.
 
mtngun said:
Brad, you must be a good photographer, because your closeups of the ports are awesome. Keep 'em coming.
Click to expand...
Good equipment helps:) The problem I have is getting enough depth of field with a large sensor DSLR. So I'm having having to shoot Aperature Priority with a small aperature, and then end up having to use ISO 800 or 1600 to get enough shutter speed so as to not be blurry. That's why they're a little grainy. It's not too bad though considering the ISO is that high. The 7D does real well with high ISO. Otherwise I'd have very slow shutter speeds and have to use a tripod. I'm not going there for this work.
 
mtngun said:
A peaky power band may be able to cut just as fast, but only if the operator works hard to keep the saw in its narrow powerband. My old lame 066 BB was like that. It is not missed.


:agree2: Yeah, and who wants a good ring seal or a smallish combustion chamber ? :) If that's what I wanted, I'd buy a Dolmar or a Solo, not a new Stihl 660. :chainsaw:

I guess the new popular mod on AS will be installing thicker base gaskets to reduce compression and heat, and then running the detuned saw on top of a mountain where the air is thinner, because compression is a really bad thing. :confused: Let's see those thick base gasket mods, with before and after cut times ! ! ! :hmm3grin2orange:

Brad, you must be a good photographer, because your closeups of the ports are awesome. Keep 'em coming.
Click to expand...

I hear ya on the peaky powerband.

Choose your colour for a base gasket. :)

plastic-shim-pack.jpg
 
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mtngun said:
A peaky power band may be able to cut just as fast, but only if the operator works hard to keep the saw in its narrow powerband. My old lame 066 BB was like that. It is not missed.


:agree2: Yeah, and who wants a good ring seal or a smallish combustion chamber ? :) If that's what I wanted, I'd buy a Dolmar or a Solo, not a new Stihl 660. :chainsaw:

I guess the new popular mod on AS will be installing thicker base gaskets to reduce compression and heat, and then running the detuned saw on top of a mountain where the air is thinner, because compression is a really bad thing. :confused: Let's see those thick base gasket mods, with before and after cut times ! ! ! :hmm3grin2orange:

Brad, you must be a good photographer, because your closeups of the ports are awesome. Keep 'em coming.
Click to expand...

Interesting pic there what dyno did you use or is it really a chainsaw and funny enough the big diesels have about the same torque rise
 
blsnelling said:
I thought I'd show a few pics of my porting layout. As you can see, there's tons of room for port widening, unlike the MS660. The 660 is hugely limited by skirt width and ring end locations. The Husky has almost a full circle skirt and the rings end towards the middle of the intake.


Here I've marked the tops and bottoms of the intake and transfers, original port width, desired port width, and ring end pins.

Here you see the skirt edges, original port width, desired port width, and port top and bottom.

879251925_DbCVG-M.jpg
Click to expand...

Curious, what's your process of finding and marking the desired port width?
 
Thorcw said:
Interesting pic there what dyno did you use or is it really a chainsaw and funny enough the big diesels have about the same torque rise
Click to expand...
Sorry about not explaining the pic. I loaded the pic intending to give a little lecture on typical chainsaw powerbands, but then decided that I, as a relative newbie to chainsaws, am not the right person to give lectures.

But since you asked .......:laugh:

It's from TW's 460/660 woods port thread. It's TW's computer model of a Stihl 460 before and after the woods port. It is not an actual dyno run, though TW does have a dyno.

TW's dyno
attachment.php


Interesting observations from the 460 power curve:

-- The stock 460 power is pretty flat from 9000 to 13,000 rpm. That's good -- it should cut equally fast at any speed in that range.

-- The woods port 460 does not have a flat power band. Still, it makes more power and should cut faster at any RPM above 7000.

-- The woods port 460 peaks near 15,000 rpm. That's not so good, but typical for a ported saw.

-- The woods port 460 makes LESS power than stock below 7000 rpm. No one cuts below 7000 rpm, so it is of no consequence, but it does show that porting may hurt the low end. That's where higher compression helps, boosting the low end and mid range. I believe TW did do a pop up on this 460, if he hadn't, the loss on the low end might have been even worse.
attachment.php
 
mtngun again I a agree with you, you have way more experience and knowledge than I. My query is, in a good running saw, does 10-20+ pounds of compression really give you much? My conclusion is probably very little. I'm all for better compression, because within reason it equals more power, I just think you need more than 10-20 pounds before it makes a noticeable difference, but I could be wrong.:dunno:
 
parrisw said:
Curious, what's your process of finding and marking the desired port width?
Click to expand...

The intake and exhaust are both 70% of bore in width.

I make the vertical lines using my dial caliper. It's made such that the end of it will set square on the bottom of the cylinder, and then with opened and the "pointy thingy", lol, sticking out and down into the cylinder, I can make my vertical lines. For the horizontal lines I use one of the rings and push it into the bore with the piston to keep it square. I use a fine tipped Sharpie to make the marks.
 
The 390XP is now ported and back together as well. It's turning identical RPMs to the 660. I have it tuned to 13,900-14,000. 14,300 is the max I would cut with it.

Here they are. Neither have seen wood yet. That may not happen until tomorrow. I have obligations tonight.


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