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372 with 268xp piston help

smokey7

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I dunno if id want more compression my 2 series saws 205 is tricky to start unless you bump it over tdc. 372 would be nice since they have a decomp. How they start with over 200? Drop start my 630 at 205 without it past tdc and its like its locked up
 

Czed

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I was hoping this 268 piston would hold me over for a little while until I’ve finished some other projects and can afford getting the saw ported and done up right. I just figured I can always pull the piston out and have it ported later
I like the pop ups i have a 268 50mm and a 272 52mm for a big bore.
Over 20 gallons through the 268/372
Against my 50mm and 52mm 372s the popup saw's are more powerful
And have better torque.
Good cheap simple mod
My friend had me build him one
After trying mine lol
 

David Young

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I like the pop ups i have a 268 50mm and a 272 52mm for a big bore.
Over 20 gallons through the 268/372
Against my 50mm and 52mm 372s the popup saw's are more powerful
And have better torque.
Good cheap simple mod
My friend had me build him one
After trying mine lol
Do you use the slab sided pistons?
 

RIDE-RED 350r

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So, you're putting a windowed piston with a taller pin-crown height popped-up for squish clearance in the bottom fed transfer 372 cylinder.... Interesting. :)

Or was the 268 an open port with a solid piston?
 

old guy

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The comp on mine only went to 172 lbs.
It was gasketless with the stock piston, but used a gasket with the 268 piston, so comparison is ?
Previous comp had been 154.
I used an unwindowed piston.
 

MotherGoose

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I’m using the windowed piston. I wonder what the differences would be in the windowed and non windowed in a 372
 

Czed

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Do you use the slab sided pistons?
Windowed
20170924_123736.jpg ft pistons the scalloped? 268 and windowed 272 used cabers.
I'm going to try full skirt next
Have to find someone to cut them.
They ended up in the 170s
This was a 372 bigbore i had just assembled.
 

frag-88

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Try on.
Oem 372xp and meteor 268
IMG_20181106_095801.jpg IMG_20181106_095702_HDR.jpg IMG_20181106_095625_HDR.jpg IMG_20181106_095541_HDR.jpg
 
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frag-88

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IMG_20181106_163852_HDR.jpg IMG_20181106_163833.jpg
With pop up piston numbers no base gasket :
sq 0,024"
Ex 108
Tr 132
In 80
 

smokey7

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WOW that is a big popup!!!! How tall is it? Most try to keep .100 above the top ring. If Kevin did it im sure its right. But if you have squish close to .020 thats going to have over 225psi id bet. Ive found with my builds in 2xx series saws i prefer no more tgen 190psi. Numbers seem ok. Id raise the transfers a few degrees after running it first of coarse. Id bet it would have very good torque with a low exhaust and transfers. I think my best runner is a 670 with a 268cp top end is 102 122 80.
 

huskihl

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WOW that is a big popup!!!! How tall is it? Most try to keep .100 above the top ring. If Kevin did it im sure its right. But if you have squish close to .020 thats going to have over 225psi id bet. Ive found with my builds in 2xx series saws i prefer no more tgen 190psi. Numbers seem ok. Id raise the transfers a few degrees after running it first of coarse. Id bet it would have very good torque with a low exhaust and transfers. I think my best runner is a 670 with a 268cp top end is 102 122 80.
The one I did for @MotherGoose was only .030 or .040". I didn't do the one above^^
 

frag-88

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I was wrong to count all the parameters without a gasket. and originally wanted to leave the gasket...
well, the saw is almost assembled, we will try what happened. At what speed does this project work?
IMG_20181116_144630.jpg IMG_20181116_122318_HDR.jpg IMG_20181116_144617.jpg IMG_20181116_153347_HDR.jpg
 

frag-88

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Squish 0,024" with no base gasket.
initially, I planned to sharpen the piston under 0.024 with the base gasket, but made a mistake and added the size of the gasket...
 

Leafy

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When i put the 272 piston in my huztl big bore i took it all off the squish because my cylinder was mis machined and you can cut the squish band without machine tools. I'm fairly certain that even if you have the gusto to drop start this saw without the decomp that you'll just break the starter. And after the last top end swapped on a saw I'm not even sure i want to build high compression saws any more, low comp seems stronger.

The 2 series piston is nice for the reduced weight, seems to make less vibrations in the saw. I'm tempted to 3d print some nylon piston stuffers that snap into the 272 piston to get the case compression back up to stock or more.
 
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