Moroso block filler

Hey guys,

I'm currently building my 4G63 evo 5 engine that has been average 1/2 filled with moroso block filler. Recommended piston to wall clearance is 0.0035". Should I increase this alittle maybe 0.0005" more or leave it as is from manufacturer spec. Aim is around 900whp, not daily just a weekend / 1/4 mile track.

More discussion points, as there are folks very experienced with these engines that may better advise you.

The grout is used to strengthen the bottom end of the block, with the upper section still water/liquid cooled. As such, the running temperature of the upper bore will be about the same and so the 'hot' diameter about the same.

However, because you're running a lot more heat into the engine's cylinders, the piston can be expected to run hotter and expand more, which would suggest a little more clearance would be a good idea - same principle as running more ring end clearance.

I would hope you're using aftermarket pistons at that power level, so I'd go by what they advised* - certainly NO less, and I'd be dis-inclined to run more than recommended (if on a fresh bore), as the greater the clearance the greater the piston rock and instability, which increases ring leakage. On that, I'd be looking at gas ported rings, as wear isn't really going to be a concern.

*make SURE!!! you have the correct piston, especially the correct alloy, as the clearances for the two most common alloys are quite different!

Hey, thanks for your input bro, they are diamond racing pistons ( 2618 ), with lateral gas ports. There specs are .0035" PTW clearance