A Tale of Three Saws

[JT78]

Sorry to jump the thread back to the middle but I have been away and just got the chance to get on here and start reading this thread and I have to clarify that the 7900 video of little possum running a 7900 at the nc gtg was NOT my saw it was done by someone else. I dont want anybody thinking that I would take credit for someone elses work. I do have a ported 7900 that I did but I know it is not as fast as the saw that Joatmon carried to the nc gtg cause I do know who ported that saw and I am no where near that level of knowledge.

 

[MCW]

opcorn:opcorn:opcorn:

And the real fun begins

 

[blsnelling]

opcorn:opcorn:opcorn:

And the real fun begins

Yeah baby! Slap some 32" bars on there and hit the hardwood!

 

[MCW]

Sorry to jump the thread back to the middle but I have been away and just got the chance to get on here and start reading this thread and I have to clarify that the 7900 video of little possum running a 7900 at the nc gtg was NOT my saw it was done by someone else. I dont want anybody thinking that I would take credit for someone elses work. I do have a ported 7900 that I did but I know it is not as fast as the saw that Joatmon carried to the nc gtg cause I do know who ported that saw and I am no where near that level of knowledge.

Although I'm on the other side of the world and none the wiser kudos for letting people know.

 

[MCW]

Yeah baby! Slap some 32" bars on there and hit the hardwood!

:smoking:

 

[JT78]

Sorry Brad not trying to jack your thread just had to get that off my chest I dont want any confusion on that matter.

This has been a wonderful thread and I cant wait to see all three saws run ported I dont think I missed it did I?

 

[blsnelling]

The only problem is that I think it's all much bigger than 32". That presents a problem for measuring cut times.

 

[MCW]

The only problem is that I think it's all much bigger than 32". That presents a problem for measuring cut times.

Maybe you can cut the sides off mate? Semi slab it so to speak

You always start posting when I have to go to bed over this side of the world Then I'm late for work when I wake up and have to read everything!

Worth it though...

 

[blsnelling]

Maybe you can cut the sides off mate? Semi slab it so to speak

Excellent idea. I'll just noodle off the front and back sides.

You always start posting when I have to go to bed over this side of the world Then I'm late for work when I wake up and have to read everything!

Worth it though...

Sounds like a personal problem:greenchainsaw:

 

[FATGUY]

Matt, I don't think that's uncommon. There's at least one machine shop that would be a lot more productive if it weren't for these threads (actually this site gneral) :monkey:

 

[parrisw]

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.

Thanks!

 

[mtngun]

mtngun again I a agree with you, you have way more experience and knowledge than I.

No, I'm strictly a newbie at the saw modding game, and have never raced, and probably never will. You've been playing with saws far longer than me.

My query is, in a good running saw, does 10-20+ pounds of compression really give you much?

I can tell a difference on my milling saw. I can even tell a difference in how the saw runs on a cold day, when the air is denser, vs. a hot day. Compression gives it more grunt, it doesn't bog as easily, and it's easier to operate.

Anyone who has ever cut wood at high elevation, where the saw loses compression and power, has noticed a difference.

Whether a cookie cutter would see a difference in times, I don't know, perhaps depending on the diameter of the cookie. I give Brad credit for using big rounds in his tests, so the saws have to work hard.

There are compromises with any mod. A pop-up, or merely tightening the squish, increases intake duration, which may actually hurt the low end. Without a dyno, or at least a good computer model, we're just fumbling around in the dark.

However, TW does have a dyno, and he does have computer models. That's why I posted his power curve for the 460. Unlike me, TW is in a position to say whether a particular mod helps. If a pop-up didn't help, I don't think TW would do it. And what he has said about the 066/660 is that, in the old days, all you had to do was drop the squish, but with the new jugs, a pop-up is the way to go.

158 psi doesn't sound so bad, but that would only blow 135 psi where I cut. If it were my 660, I would absolutely do a pop-up to get the compression back up.

 

[Jacob J.]

20 psi makes a huge difference when you're cutting under commercial conditions and making a living with a saw. 20 psi might mean the difference of getting another 25-30 trees on the ground in a straight falling job. That translates into $$ when you're cutting stuff that's going 30-40 trees per load and you're getting $125 per load.

 

[blsnelling]

Compression on the 390 is now 155 since tightening the squish. The 660 is still at 158.

 

[edisto]

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

In actual width (chord), or along the circumference of the circle (which is closer to a width of 65% of bore diameter)? I know I've asked you this before, and I'm only asking now because you used to go 70% along the circumference, and your post implies the actual port width is 70% of BD.

 

[blsnelling]

In actual width (chord), or along the circumference of the circle (which is closer to a width of 65% of bore diameter)? I know I've asked you this before, and I'm only asking now because you used to go 70% along the circumference, and your post implies the actual port width is 70% of BD.

I went a full 70% along the chord.

 

[edisto]

I went a full 70% along the chord.

Go big or go home!

 

[blsnelling]

Go big or go home!

Oh yeah! Too bad the 660 is so limited by skirt width. I also couldn't widen the 660 transfers like I wanted due to the ring ends out past the edges of the skirt. While both saws are turning the same RPMs, I fully expect the 390 to come out on top because of these porting limitations.

 

[flushcut]

opcorn:opcorn:opcorn: I can't wait to see the end results.

 

[TRI955]

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.

Can I see some kind of demonstration on how to do this, make the vertical lines that is. Maybe a picture??