It's widely accepted that Piston Slap is caused by wide tolerances between the bore and piston skirt at time of ignition during colder temp startups. And I think it usually is, born out by fact it's fairly quiet until you call for power
But I always wondered, what if it's more than that? What if carbon is built up on the piston and head and they are actually colliding?

Read this and see what you think:
Does this make sense to remove carbon buildup? Piston knock [Archive] - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

I know for a fact that exercised -not abused- engines run better and last longer.. in fact it's one of the first things I learned as a kid. I had a 51 ford flathead that I and my dad before me ran the **** out of. I was unfortunate and dumb enough to pull out into an intersection without looking {Maybe having two cheerleaders in car distracted me} and got T-boned by a VW bus. So I got another 51, pretty cheap though it was in real nice shape because it had been babied. Good in a lotta ways bad in others. Wasnt two weeks till I blew the engine. Because it had never had 'the carbon blown out' as my dad told me.
My first real wrenching.. swapping the old engine from my wreck. By myself. Dad only drove front-loader when I dropped engine in, so nothing got crushed.

And I really ran the hell out of my SVO 2.3L turbo.. at 18 lbs boost no less.. for over 185K miles. Only thing put an end to that was an exhaust port crack.

But bearing and bore tolerance were still on the dont need rebuild side of the specs. And you could eat off the piston tops.

Do I advocate going WOT for us? Not unless you do an intake Seafoam first! Then check the chambers with a borescope.
But once you do that, maybe it would be a good thing to let the dogs out a couple times a week.

 

You're talking about an 'Italian tune-up'? I just don't think that it's as necessary with modern engines as it was with the ones we grew up with due to engineering and design differences, but a good cleaning out once in awhile shouldn't hurt.

GM piston slap seems to be more prevalent on the V8's from a certain period (early 00's) than on our V6 even though it is from the same block and can, and has, occured. I don't think carbon build up is connected to it although the infamous slap has been incorrectly diagnosed before.

 

In my experience carbon buildup has nothing to do with piston slap. My previous 2000 SS Camaro had 10k miles on it when I bought it on 2007. It had piston slap from day one of me owning it. I put a cam in it at 16k miles and drove the **** out of it for the next 20k miles and the piston slap was still the same. Also to make mention, my PTV (piston to valve clearance) was obviously closer with the more agressive cam. Put a 100 shot of nitrous through it shifting at 6600 rpm for a few months before I sold it as well and never noticed anything different as far as the piston slap.

My buddy has a 2000 SS Camaro with a 408 in it and his pistons were all sorts of Carbon'd up when he pulled the heads for his turbo build. He was running rich as hell before that though due to a crappy tune. His car never had piston slap at all.

I don't drive my other vehicles like I do my "fun" cars, however they do get a good WOT run in every now and then. My newer to me Camaro will be getting upwards of 15 psi pushed through a stock bottom end 104k LQ4 and making 600+ at the tires. It will be getting a good WOT run every time it comes out of the garage.