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

 

make him buy you a new block....

 

So in other words... I should be worried?

 

There are so many variables with this it is hard to say. The very temperature of the block, especially aluminum, can change the tollerences(i'm talking 20* or more). Another thing is if the block was honed with torque plates. If so, it will measure more loose without the tq plates installed. Also, if it was measured with a dial bore gauge, T gauges or inside mics will change with mechanical or operator error.
Basically, the thickness of a hair is .002-.004". I'd compile info and have a 3rd or 4th machinists' opinion before you threw the machinist under the bus.
Besides, all gen3 engines have piston slap when cold due to short piston skirts.

Personally, i'd run it. Loose is fast.

 

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?

 

Im almost positive they are a 4032. I told him the pistons I planned to ordered before he had the block but when I gave him the block and everything for the machine work... I gave him everything he needed... pistons rods.. blah blah. I didnt really tell him any bore size or anything though, I figured he would know better than me.

These were what I ordered so I can run a 6.125" rod

http://www.texas-speed.com/shop/item...d=125&catid=38

 

I would bet on that if you called Mahle, they'd say it was within an acceptable range. Especially if you ever plan to run any kind of power adder, which require more tollerences to be safe.

 

Ya, the guy who is putting it together did infact call Mahle and they told him they thought they would be ok... I am gonna give them a call myself and see though.

I do eventually plan to run nitrous but that wont make much of a difference for everday driving like boosted would.

 

Maybe, but Running that style of piston too lose will do nothing once you start spraying.. they dont expand with heat. Hopefully you are within range as turbogibbs said.....

 

how much n2o?