Mastermind Meets The MS660

[Mastermind]

What I'm most impressed with that you got the compression back up to 170psi without putting a head on it!

It had 220 or so before I raised the exhaust...

 

[FATGUY]

we could probably squeeze a little more out of it, (I mean compression and not just squeezing the bottom of the piston)

 

[Mastermind]

I'm close to 200 PSI with the exhaust at 97° on my 390XP. Surely another 8°-12° wouldn't kill it The intake is already plenty low enough.

Most importantly is transfer area in a saw that you want to really run. Well that and carb.......and ignition......

 

[FATGUY]

It had 220 or so before I raised the exhaust...

those thick bases make it nice don't they?

 

[Mastermind]

I'm close to 200 PSI with the exhaust at 97° on my 390XP. Surely another 8°-12° wouldn't kill it The intake is already plenty low enough.

we could probably squeeze a little more out of it, (I mean compression and not just squeezing the bottom of the piston)

I sense a plan being formed....... :msp_sneaky:

 

[Mastermind]

those thick bases make it nice don't they?

Yes but the "black ring of death" is not so nice. It would have had more compression but for that SOB....

 

[blsnelling]

It had 220 or so before I raised the exhaust...

Wow. That's a lot of compression loss! We went .035" on my squish band. Anyone ever try doing that and a popup? At some point it's got to be easier to just chop the head and put a 2-piece on it.

 

[gink595]

I bet you'd be surprised at what 12-15* will do for your compression. I know I was Yeah I think a head would be the best way to do it, makes it easier to port too.

Here is a head I just made for 66 bb.

 

[Mastermind]

Wow. That's a lot of compression loss! We went .035" on my squish band. Anyone ever try doing that and a popup? At some point it's got to be easier to just chop the head and put a 2-piece on it.

That's what I've done on this saw........get outta muh head Bradly.

 

[blsnelling]

That's what I've done on this saw........get outta muh head Bradly.

I honestly didn't know that, lol.

 

[FATGUY]

Yes but the "black ring of death" is not so nice. It would have had more compression but for that SOB....

:bang: damn it, if it ain't one thing, it's another. A man could do well for himself if he could find a cost effective way to replate cylinders....

 

[Mastermind]

:bang: damn it, if it ain't one thing, it's another. A man could do well for himself if he could find a cost effective way to replate cylinders....

I have this ms390 jug I've been looking at...........if I bored it to 52mm....... :msp_sneaky:

 

[splitpost]

you could cut the head off,over bore it,fit a stepped liner blank and then go to town on your ports but jeez thats alot of work ,could be a fun saw though

 

[splitpost]

you could cut the head off,over bore it,fit a stepped liner blank and then go to town on your ports but jeez thats alot of work ,could be a fun saw though

Thought this would get you thinking MM,not kill the thread

 

[stihl038x2]

Is anyone cutting thier squishband on a taper ? & stepped like the factory jugs ? Do you think it matters ? It's not much more work once you are in there anyhow. I've done a couple that way but am unsure if it is any better, the factory must do it for a reason, Jennings or Bell have probably addressed it but I don't have their books & can't download them, besides I don't like reading books on the "puter"

Steve

 

[tlandrum]

if you cut it on a taper it directs the flow into the chamber better than it being flat but i dont think you could notice a difference even with a stop watch.

 

[wigglesworth]

Is anyone cutting thier squishband on a taper ? & stepped like the factory jugs ? Do you think it matters ? It's not much more work once you are in there anyhow. I've done a couple that way but am unsure if it is any better, the factory must do it for a reason, Jennings or Bell have probably addressed it but I don't have their books & can't download them, besides I don't like reading books on the "puter"

Steve

I've been putting a slight taper on the ones I've done. Usually around .010 rise from the cylinder wall to the combustion chamber. I've also done em flat.

I haven't noticed a difference either way, but I'll be honest, I've only done a handful....

IIRC, I think in Jennings book, he states that the dome piston/combustion chamber combo makes more HP, due to the increased square area of the piston crown. I'll have to get a lot better on the lathe before I try that out though.

 

[parrisw]

I'm only on my second one but been cutting the chamber on a 2* taper. Been thinking of trying a taper on the crown with a 2* difference between the squish band, like 4* on the squish band and 2* on the piston.

 

[wigglesworth]

I'm only on my second one but been cutting the chamber on a 2* taper. Been thinking of trying a taper on the crown with a 2* difference between the squish band, like 4* on the squish band and 2* on the piston.

I would "think" anything you can do to help get flow to the combustion chamber would be a good thing. But I've seen some CRAZY wide and flat squish bands, with tiny combustion chambers that were serious runners.

I also "think" the angle of exit on the upper transfers has a lot more potential to help flow twords the chamber than the squish band angle.

 

[parrisw]

I would "think" anything you can do to help get flow to the combustion chamber would be a good thing. But I've seen some CRAZY wide and flat squish bands, with tiny combustion chambers that were serious runners.

I also "think" the angle of exit on the upper transfers has a lot more potential to help flow twords the chamber than the squish band angle.

I'm thinking under compression though. Plus a tapered crown has more surface area, more area for the combustion to push on, more HP.