what piston to wall clearance, are people running? I've got cp pisston, cp recommend .0045 piston to wall clearance.

my friend's build ej25 has cp piston and has 3.5 thou piston to wall clearance, on cold start piston slapping against bore very loud, he also has oil consumption issue's.

Would having 2.5 thou piston to wall clearance to tight?

 

my Mahle 4032 are at .003 but I understood the Mahle ran smaller clearance. The car uses virtually no oil.
Trev

 

depends how much the pistons expand, as some expand more than others
it also depends on the application

 

0.0045 is huge .. Trevs 4032 Mahle are high silicon that don't expand much so can be tighter (and quieter)
Mahle 2618 are low silicon and need a bit more, but given the first time an engine fires up the clearance immediately increases (due to surface finish change) then even 0.003 is a touch high
3.5 should not be too big (relatively) but did he gap the rings correctly and position them on the pistons correctly, can make a big difference to oil consumption

2.5 is probably too little for a 2.5 litre piston

Some pistons are simply "loud" and CP are like that, when it was bored and honed was ovality checked ?