Not so. Several of us have modded stratofied saws with good success. But that's an entirely different discussion.
Guess this piston
- Thread starter blsnelling
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Not so. Several of us have modded stratofied saws with good success. But that's an entirely different discussion.
AUSSIE1
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Good stuff Brad.
Did you notice the 390XP has the cyl at the lower transfers raised similar to what you've done here?
Works for 385/90 so worth a go.
Would be interesting to see what your piston weighs against an 064.
I'm bettin yours could be lighter.
Husky's thoughts look like they wanted the rear lowers angled toward the front, but matching to the crankcase makes more sense to me.
Did you notice the 390XP has the cyl at the lower transfers raised similar to what you've done here?
Works for 385/90 so worth a go.
Would be interesting to see what your piston weighs against an 064.
I'm bettin yours could be lighter.
Husky's thoughts look like they wanted the rear lowers angled toward the front, but matching to the crankcase makes more sense to me.
bitzer
******** Timber Expert
No I know i've seen em in vids on here. Just a new challenge to overcome. Mine is really limited I believe. I'm sure if I gave it to you or another builder that has done lots of saws they would have more ideas that I haven't, but then I think to myself its only 56 ccs and I got it brand new for $200. I think i've got what i've got out of it! Well other than a pop up! Thanks again.
tdi-rick
Addicted to ArboristSite
IMO this is pretty much all a 7900 piston window does.
Lightens the piston, cools the crown and increases lubrication to the gudgeon (wrist) pin bearing. The transfers are fed from the crankcase.
AUSSIE1
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Guess I was too excited when the teacher asked the question and just got my hand up and blurted out the answer before I even turned the page! ......
Now.....I have the same cylinder and piston here on my desk waiting for the grinder. Plan was to leave the transfers at the same opening but slightly wider towards the intake side, square up the bottom of the intake, widen exhaust, do the bottom of the transfers just as you have, then use an 064 piston ( Meteor - also here on the desk) with a pop up that equals the gasket thickness plus a decent squish. The 064 piston is windowed, the rings are pinned in the wrong places and the inside rod opening is too small. So now it's back to the BB piston without windows and I will take what I need for squish from the gasket surface and use that for a popup......Plans Change....Thanks for your willingness to share......
Farley, with the piston reversed, your rings will clear.
The piston windows are just one piece of the puzzle though. My 372BB has never been as strong as my 460 or 440. I know it can be. So I went back in yesterday to see what I could do about that.
I started by raising the cylinder wall at the transfer opening at the base of the cylinder. I raised it by nearly 1/4". I wanted to open up the area where the transfers take in from the crank case. If the cases were split, I would have case matched those as well.
This opened up and created a dead space on the side of the piston.
So I got to thinking. Other saws have ports that are setup similiarly and have windowed pistons. Not only would that open up that dead space and allow it to be pushed into the transfers, but it would also aid in cooling the underside of the crown, and significantly reduce piston weight. What's to loose? So I threw caution to the wind and decided to try it.
But why the need for all the extra intake area? Well this is the main thing I was after here. I need more transfer area and timing. I raised the transfers a huge 8° and significantly widened them. I didn't not go all the way to the vertical lines, but you get the idea.
Here's the end result.
Ho ####.:bringit:
FATGUY
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I'm looking roward to watching this one!
outdoorlivin247
Addicted to ArboristSite
Hey boy. You're going DOWN....................HARD!!!!!!!!!!!!!!!!!!
breymeyerfam
Addicted to ArboristSite
sean, i think it must be an Ohio thing...
Not me man.
With all the work you put into that saw I hope I do go down.
Gettin' sceeeered?
Good video Brad. If I had all the speciality tools, I'd do that modification to my 390XP. Thanks for sharing your work.
A little.:Eye:
husky362
ArboristSite Operative
i've widened the ports on my bb , what kind of gain would you get just putting the windows in, adding the lower port and working the transfers in the jug, everything else being stock
parrisw
Tree Freak
Pretty cool Brad!! Got me thinking now!!
Bowtie
Gearhead
Yep, me too. I did what Brad did except I DID NOT add the piston windows (yet). I wonder if raising the base of the cylinder transfer slots will improve flow in combination with opening up the transfer uppers toward the intake side? Im gonna see if I notice a difference tomorrow.
The reason I went past that and did the windows was because raising the cylinder walls opened a large area of dead air space. Actually I'd love to see you run it like it is and then add the windows once you have a feel for it. I did a lot of mods at once, so I don't know which one did the most. But then again, it's the cummulative affect of all mods that adds up.
Bowtie
Gearhead
Right on, I will try it like it is. I didnt open my transfer uppers quite as much as you did, but close. Kudos to you for having the kahunas to try that and to post the info and pics!
