So, second part of my now build/rebuild is not using the stock piston. In the week I have been on just a Facebook group for this engine, 3 piston failures. All of the breaking apart at the ring lands and crown. A couple on the skirt.
I am not yet decided on what route I want to take with the piston yet. One thing I do know, I am NOT using the stock piston. The casting quality and ring quality aside, the piston wall clearance is grand canyon levels of huge.
My first option is an MS460 piston, which is .12mm taller in crown height over the stock piston, so I still have a ton of room with the squish gap before it becomes an issue. It also uses the same exact type of rings at 1.2mm, and the one I ordered is a pop up piston and it came with Caber brand rings. One slight upgrade, besides a small bump in compression, would be the fact that the piston ports for the transfers are a good amount larger than the Phantom ports.
This is the stock vs. MS046 piston transfer ports. If I had to guess, they are about 30-35% larger.
The second is an MS380 piston. This piston could work, and in terms of performance has the greatest potential. It's 1.2 mm taller in crown than the stock piston. As it stands, this means my squish gap is negative. On the plus side, this does mean that I could mill the top of the piston down and precisely set my squish gap to whatever I want. If there was any real drawback to it over the 046 piston, it would be the thicker 1.5mm rings. It's not a big difference, but extra drag does mean lost power.
On the plus side, the piston transfer ports are flipping enormous in comparison to the other two pistons. I would hazard a geuess of close to 60-70% larger when compared to the original Phantom piston. This means at higher RPM there is greater potential airflow, which makes up for the thicker rings a bit.
The other issue is that it uses a 13mm width needle bearing over the 15mm of the 460 and stock piston. On the plus side there are needle bearings that work, and the rod end at the wrist pin is a hair over 11mm wide, so there is plenty of room to work with.
I am still up in the air about windowing whatever piston I choose or not. A part of me thinks this engine could be a little softer in the low end power and make up for it with higher RPM power. A non-windowed 038 piston with some careful port work could change this motor into something a bit more reliable without sacrificing the upper RPM power. We shall see.