Mastermind Meets The 372XP.........Again

[Mastermind]

 

[Mastermind]

Before and after.......

 

[smokey7]

Wow lots of grinding on those. Is it my eyes or do you leave one of the lower transfer ports untouched? If so why is that?

 

[XP_Slinger]

Nice work Randy. Thanks for taking the time to post all the pics.

 

[Adirondackstihl]

Nice beveling bro!!

 

[Derf]

Seeing how the upper and lower transfer ports get so much bigger makes me think transfer velocity slows waaaay down and suffers for it. But maybe it just seems that way because they were so small to begin with? The final 372xpw transfers might be flowing the same as the regular 372xp transfers when all is said and done.
Although you say it wouldn't be your first choice to start with the 372xpw jug, I wonder if that's just because it requires so much grinding work to realize its full potential?

 

[Brush Ape]

Starting on the uppers.

Oh no that's what Elvis did.

 

[Mattyo]

That's nice grinding mm.

That 51.4 jug is annoying because there is no aftermarket piston available. If you toast a piston. ..it's $80 for oem....which you are stuck with.

I'm just not sure the extra gain is worth that annoyance to me. But then again....maybe there is a lot extra to gain lol. I'm sure mm will let us know

 

[Derf]

If you toast a piston. ..it's $80 for oem....which you are stuck with.

I'm just not sure the extra gain is worth that annoyance to me.

If you don't lend out your saw, you significantly cut down on the chances of straight gassing your saw, which is the #1 reason I've seen for toasting a piston.

 

[Mastermind]

Wow lots of grinding on those. Is it my eyes or do you leave one of the lower transfer ports untouched? If so why is that?

The main transfers ports are the ones that are choked off by the designers. The secondaries are pretty much the same in the 50 and 51.4mm jugs.

So, I enlarge the mains and open them a few degrees before the secondaries.

As big as the mains are, opening them first allows them a chance to get moving, and hopefully bring volume to the party. Then the faster flowing secondary is aimed upward, and opening later should push the charge up into the chamber rather than allowing it to short circuit out the exhaust port.

Of course all this is just a theory, and could be way off of reality.

 

[Mattyo]

Man I was wondering if you had the mains opening first. I could have sworn so in the photos.


...but isn't it more usual to have the secondary open first?

 

[Mattyo]

If you don't lend out your saw, you significantly cut down on the chances of straight gassing your saw, which is the #1 reason I've seen for toasting a piston.

Orrrr. ....how about not torquing down the carb bolts quite enough....so you get a leak at the boot/carb jxn and toast the nicest saw you ever made in abut 10 min?

 

[Mastermind]

Man I was wondering if you had the mains opening first. I could have sworn so in the photos.


...but isn't it more usual to have the secondary open first?

Lots of ways to skin a cat...

 

[Mattyo]

Sounds like a different cat to me....

 

[Mattyo]

ok, serious question... on the lowers, since you are significantly increase the size of the main lower by grinding that stump back, when you grind on the divider, why not grind the divider in favor of increasing the size towards the 2ndary lower? ... so as to have more even flow for both?

 

[Mastermind]

ok, serious question... on the lowers, since you are significantly increase the size of the main lower by grinding that stump back, when you grind on the divider, why not grind the divider in favor of increasing the size towards the 2ndary lower?

I thought I explained my thinking already......but I'll try again.

I'm looking for volume in the mains, and velocity in the secondaries.

 

[Mattyo]

now I gotcha .... ok

 

[MustangMike]

Would be interesting to see saws done each way compete. Since the port starts as a single hole, whey you open the mains it should reduce pressure to the secondaries.

 

[Mattyo]

I guess I really just have hardly any clue as to what is going on inside the motor. I can visualize it... but it just seems so complex that ...its just too serious for me lol. I like things laid out much simpler. So it make sense that you'd want velocity for the wash on the secondary, and the main for ... oompf... for where the majority of the air/fuel mix gets deposited.

If then though you want velocity on the secondary, wouldn't keeping the 2ndary as narrow as possible at upper be the objective? ... and wide at the lower so as to cram as much air/fuel as quickly as possible.... like a bottle neck?

 

[Mastermind]

If then though you want velocity on the secondary, wouldn't keeping the 2ndary as narrow as possible at upper be the objective? ... and wide at the lower so as to cram as much air/fuel as quickly as possible.... like a bottle neck?

Could be I suppose. In the past I've opened up more of the transfers than what I've done here with less than stellar results. Take out too much material, and it makes a engine that is lazy to spool up.

What I've really done here is try to make this cut off saw jug match the chainsaw jug. If you look closely at the pictures they may explain better than I'm able to.