GEN V and VI come with "Over-hyped-you-f***ed-me" Hypereuctetic) pistons. They are fine with a stock or low performance engine only, you can get away with them at a slightly elevated HP level if the cooling, clearances, timing and jetting are near perfect. More power, or any one or several of the issues mentioned and you break skirts first, then above that, the piston is gravel in the pan, and the pin and top of the rod make a big hole in the cylinder wall. Go forged if you want to make power, and find a machine shop that KNOWS BOAT MOTORS!!!(OK, this time I'm yelling). The number one problem we see at our shop is freshly built jet boat engines with cracked or shattered pistons, and usually after only a few outings, if cammed, manifolded and big headed. We have two in here now...
Lets do a comparison of cast, hypers, and forged pistons on a scale of one to ten:
COST and STRENGTH
CAST 1 1
Hypereuctetic 7 2 or 3
FORGED 10 10
Why pay the big bucks for something (hypers) that is only marginally stronger than cast? For a stock or near stock engine use cast, anything else, use forged. There was a very good HOTBOAT article about this subject, find it, read it, and post it. I can't, (legalities, I wrote it).
Hypers came out when the Federales mandated 50,000 mile mandantory smog compliance to the vehicles original owner. The factories needed a harder piston that wouldn't wear as much in the ring grooves or skirts, and could run at less clearance, all to help the smog deal. A large cast piston company knew that adding more Silica (sand) to the aluminum piston would make it harder, and they spent big bucks to conceive a way to take a normal cast (Hypo-euctetic) piston and add more sand than would normally stay in solution when cast. That's considered a Hyper-euctetic solution.
Take a glass of iced tea (no sugar) and stir in sugar slowly until no more will dissolve into the tea, that's a Hypo-euctetic solution. If you add more sugar than it can hold at that temperature, the rest just goes to the bottom, and its still a Hypo-euctetic solution. If the temperature is raised in a very controlled manner and put in a preheated mold, JUST RIGHT, then the extra sand will stay in suspension and cast well. The extra sand makes the aluminum harder, that's what was wanted, but it also makes it more brittle, NOT what we want in a performance piston.
When GM first started putting the Hypers in all of their engines around the late 1990s (my brain is foggy about the date , not the facts) we R&R'ed at least 4 or 5 sets of them a WEEK for a local dealer, some with only "Black Death" (localized overheating and micro welding) on the skirts to siezed or exploded pistons and blocks that needed honing or replacing. We did those for about 2-4 years before they were all fixed or blocks replaced and honed as required. The rest of them were sold to old folks and peeps that babied their stuff until the wall clearances opened up. Many second owners got those babied cars/trucks and killed the pistons in the first weeks of ownership, and we did a lot of stockish motors. We always add at least .001 piston/ wall clearance minimum, and to this day do not install hypers unless its a stock or mild deal and we still add .001-.002 extra clearance depending upon the circumstances. We WILL NOT build a jet boat motor with Hypers at all for any reason. We are in Phoenix,AZ. and it gets to 110-115 here in the summer, we also do lots of motors for the Colorado River folks from Yuma to Laughlin where Summer temps will go to 120+.
Back to that harder piston deal, glass is made from Silica sand and is harder than a piston, but you wouldn't make a piston from it! TIMINATOR
