ive been doing some research and had bought some KB 107's to use in my 360 build, but have had 2 builders refuse to use them, saying they have a tendancy to break...crack right down the middle. has anyone had any experience with this happening? these are VERY well known engine builders, not just local guys
Some people have trouble with KB pistons when they don't follow the correct ring gap specs. Their Hyper-whateveritis pistons hold more heat in the domes, so they need a bigger ring gap.
Built plenty of engines with KB pistons no problem, although if you don't make your top ring gap a little bigger you can bust the top edge out of it.
Hypereutectic pistons are not very resistant to detonation; the extra silicon content makes them stronger than a conventional cast piston, but also somewhat more brittle. In addition, United/KB has very specific instructions regarding ring gaps...which many builders, both amateur and professional, don't follow. Given these two characteristics, some people have had problems. It depends on what you expect out of an engine. It's been my experience that a lot of builders don't like hypereutectics, simply because they know that their customers will beat the **** out of them...(i.e. treat the engine as if it has $800 Diamond or JE pistons, instead of <$200 hypers). I know quite a few racers that won't consider hypereutectics for anything, even mild street engines. But by the same token a lot of these guys run forged cranks and aftermarket rods in everything "because they're better." I personally know of several engines running hypers with great success, including one with a LOT of nitrous....but, the owners all know enough to get the tune right, including both A/F mixture and the timing curve. I also know of a couple of heavy towing applications that are using the KBs as well. Only you know exactly where your level of knowledge and intended use fall into all this. I would be much more inclined to use a KB hyper over a Sealed Power hypereutectic...if those were my only two choices...
Ditto what everyone else has posted, the top ring gaps are different than a standard piston! KB is the only piston company "that i know of" that has a spec sheet in their catalog that tells you how to set them up for Nitrous!
Also, if your refering to KB's hyperutectic line make DOUBLE sure your not seeing any detonation (preignition). Hyperutectic pistons will not tolerate this type of stress. As impressed as I am for most street applications of this type os piston the one thing I've found is you can't run right on the ragged edge of preigntion like you can with a lot of forged offerings. Frank
More info on them for people that may not know: Hypereutectics are still cast pistons. They just happen to have more (hyper) silica in the alloy than will fully dissolve in the alloy (eutectic) Imagine Koolaid with so much sugar that it wont all dissolve, that's hypereutectic. Except with pistons- the sugar is silica, and it should be evenly distributed, and it helps the strength of the casting. But it's still no forging.
FINS...any good engine builder can gap the piston rings. that's not the problem, 1 must use the right pistons for each build. but again the builder will tell you what they prefer...POP.
my build is a pretty stock, LA 360 mopar. no boost. im coming from a smogger 318, that im quite sure had cast, and i ran it reasonably hard. if theyre stronger than the stock 318 pistons, then i dont forsee having an issue. i have read up a lot on the top ring gap but have had more than one builder look at me like im speaking greek when i tell them about that requirement, so i am So afraid that it wont get done right. maybe i need someone to help me build it, or just to grow some stones and build it myself. i have the knowlege but have never done it, and i wanted something with a warranty so if something wasnt right i could make someone else fix it, lol.... so nobody has had this happen in real world, proper application, and installation? that makes me feel better.
I've never seen a KB split "right down the middle, no. I have seen a couple of failures which were directly linked to detonation, and one where the top ring land failed. (The owner, when asked what ring gap he used: "Huh?") Detonation is roughly the equivalent of hitting the piston top with a hammer, and it generally causes cracks, or chunks to come off. I have seen at least two Sealed Power hypers that actually appeared to be eroding, for lack of a better word...where the piston actually seemed to be softening. I know of a couple of guys who have used them successfully, but they have recent builds and the longevity is still open to question. It sounds to me as if the KBs are a pretty good fit for you. Any competent builder (even if they haven't heard about the gap issue) should be able to take care of it, especially if you print off the relevant pages and tape them to the box. If you still have doubts, find someone else. Don't feel that you're "stone-less" if you don't build it yourself. Any jack*** can throw together an engine without specialty tools or knowledge...and sometimes they even run and last. The odds aren't real high that it will be as good as it could be, though. Building engines takes at least a minimum of expensive tools, which don't actually get used often enough to justify them, unless you do at least a couple a year. One option is to split costs with someone else...i.e. maybe he buys a decent micrometer set, and you buy a damper puller/installer set and a degree wheel/dial indicator...and so forth. I've been buying tools for about 30 years and still don't have everything I want.
The Jalopy Journal
