I had my LS1 honed and ended up going with a 3.905 Mahle Piston... which apparently the recommended bore size is a 3.908 for clearance. Well the guy putting my motor together called me this weekend and said the bore size is a 3.910... the guy who did the machine work did have my pistons/rods when he did it so it kinda pisses me off a little that its overbored more than its supposed to be but should I be worried about this? The guy putting it together said it may smoke a little and I may get a little piston slap but due to the Aluminum block theres not many other choices I have piston wise unless I start getting into something custom.

Any thoughts or suggestions? I dont know much about the clearances but he told me when it heats up it would be fine, just when I cold start it I might get a little slap and smoke.

Also... is this maybe to much of a bore on a LS1?

Thanks!

 

What type of pistons? 2618 or 4032? To my knowledge Mahle is available in 2618 by custom order only....

If they are off the shelf mahles they are 4032, in which case .005 is a bit big. They will be noise, and they are not going to expand that much once warm. That is really the only benefit from running 4032 pistons, less clearance is needed, thus longer life, and quieter engine.
Contact Mahle, they will know the amount of tolerance for those pistons.... But I highly doubt they will get quieter when warm.

By chance they are 2618, they will be fine.

I personally would make the machine shop fix this issue.. Did you supply the specs for clearance on the pistons?

 

3.910 is the max bore limit. if your running nos having .005 clearance is just fine with a forged piston. if it is too loose for you, the machinist can knurelize the pistons, which is a good idea, becuase it will hold oil and libricate the cylinder better.