|
I got my bottom end back together and was able to check the squish gaps with the pistons I have on hand. I measured the chamber CC as best as I could and came up with a 6 cc chamber. Not exact since it is a fixed head cylinder, but fairly close.
Surprisingly, with both base gaskets in place the MS380 piston actually clears. It has a fairly tight squish gap of .6mm and would give a compression ratio of nearly 12:1, which is a tad high lol. The bigger issue is it blocks the transfer ports and closes off the exhaust port, so it definitely needs to be milled down to work.
The stock piston with both base gaskets has a 1.72mm squish gap and has an incredibly low compression ratio, 8.9-9:1. Possibly a design choice to keep heat down and allow it to run on cheap gas. With one base gasket it drops the squish gap closer to something more acceptable of 1.12mm, and bumps the compression up to 10:1 With no base gasket it's right on the edge of squish gap tolerance at .52mm, but like the 038 piston the compression is near 12:1
Unsurprisingly, the MS460 piston ends up with the best overall figures. With 2 base gaskets its still nothing special with 1.6mm squish and 9.1:1 compression, but with one it has a squish gap of exactly 1mm and a compression ratio of 10.45:1. A pop up piston with 2 base gaskets lands somewhere in the middle with a 9.6:1 compression ratio while also maintaining the port timing of the 2 gaskets.
I am going to run a flat top 460 piston with 1 base gasket as I view it as the best combination overall. and then likely port the exhaust side to restore some of the lost timing and increase duration.
|