4Vman said:
Forged pistons are harder on the bores than cast pistons so bore wear will be higher, more wear = more clearance and excessive clearances can crack the piston, in theory there is some merrit in the statement that forged pistons don't last as long but there are allot of other factor including how hard the motor is reved that will determine it!!!
V8 supercar pistons would be buggered after 2000 k's!
Sorry, but there is no way that forged pistons are "harder" on an engine than cast pistons, especially the bores. Pistons do not contact the bores, so the material difference in terms of hardness can not be an issue with regard to bore longevity. Additionally, since forged pistons expand less than cast pistons (including hypereutectics), they are less prone to "rattling" in the bores on cold start-ups. If the oiling system is doing its job and slinging oil into the bores, then the skirts of the piston will properly float on a light coating of oil between them and the bore.
The idea that forged pistons do not last as long is utter BS. Perhaps more true is that engines with forged pistons tend to be hot rodded a lot more and that, not the piston material or production method attributes to lower life including faster wearing bores. Also, since you can usually rev and engine with forged pistons higher than cast pistons (assuming the rest of the engine is built to take it), more revs per minute account for greater wear over a given period of time.
Rings are what wear bores. Cast pistons expand a good bit more than forged pistons. This expansion process leaves the rings either loose or tight depending on how you look at it. Ideally, an engine builder builds for typical operating conditions and that is going to be the temperature that the piston routinely sees during normal driving conditions. When pressed into "harder" service, cast pistons oftentimes expand beyond reasonably safe limits and cause additional friction, heat and resultant wear on the bore. For this reason, hot rodders with a clue run forged pistons. Attention to proper bore clearance is of the utmost importance when fitting pistons. However, more than bore clearance attributes to fitment including rod side clearances and definitely ring end gap clearances. Another factor that can often be seen in novice engine builders is ring ends that are not filed squarely.
Bore oiling in a Cleveland is a bit whimpy, comparatively speaking. It is not uncommon for NASCAR and other kinds of all-out racers to place bore oilers in their engines.
If excessive wear is responsible for cracking pistons, then the hypereutectic pistons with their fairly notable clearance requirements (due to large expansion) are subject to such situations. However, excessive bore wear is likely to produce ring sealing issues long before pistons crack.
Every good engine builder that I know absolutely won't touch a hypereutectic piston for any purpose...and they all swear by forged pistons. The only people I've ever heard of who push the "hypers" are trying to make a quick buck and sell cheap cast crap to someone who is on a tight budget and doesn't understand what junk they truly are with regard to high performance engines. If you want to rebuild a stocker, but stocker cast pistons, not hypereutectics. If you want to build a hot rod or a race car, use forged pistons. If you're spinning your engine above 5000-5500 RPM regularly, then forged is definitely the way to go.
I wouldn't use hypereutectic pistons in my worst enemy's engine. I think that they are cheap cast junk with the thermal qualities of a high silicon cast piston. Anyone want to guess what the added silicon does to piston strength? It reduces it!
:davis: