Originally Posted By: 440Magnum
I don't see how ANY oil could have an effect on piston slap noise. Piston slap occurs when the piston is hardly moving at all- its very near TDC and the sound is caused by the piston rocking side to side in the bore as the connecting rod changes angle as the crank crosses over TDC. Since the piston isn't actually moving up and down, just quickly tilting side-to-side and the sound is the skirt clicking against the bore, how can oil affect it? I guess a REALLY thick gooey oil could muffle it slightly, but I wouldn't want all the other downsides that come with that.
Piston slap is also completely harmless, although it sounds horrible. I built one of my 440s with short-skirt hypereutectic pistons, centered-pin style (factory pistons have offset pins to reduce piston slap at the expense of more friction throughout the stroke), and the pistons are fitted on the loose end of the tolerance range to avoid any risk of galling during extended high load operation when they get fully heat soaked- which is always a risk with HE pistons. I swear it sounds like a 7.3L Powerstroke when its cold and takes a solid 10 minutes for the sound to completely go away in the winter, but it has zero oil consumption after 25,000 miles on these pistons. Fear of piston-slap is greatly overblown, IMO. People have just come to expect near-silent engines, when there's really no engineering reason for that to be necessary.
you fit hyperutectic pistons on the loose end to compensate for growth at high temps?
It is hyperutectic pistons high silicone content that keeps the pistons from growing at high temps from what I knew.
Forged pistons need extra clearence for growth at high temps, I have a set of Wiesco pistons set up at .005 piston to wall and it sounds like a diesel when I start it.
From past experience hyperutectics need only .002 for most engines, now they do have many other suggestions for other type of engine use, marine,nitrous,circle track etc etc...
Quote:
KB pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB piston allows the builder a choice without fear of piston damage. Seethe clearance chart below for minimum and realistic maximum loose fit clearance for KB pistons.
Quote:
http://kb-silvolite.com/clearance_pop.php