From this side of the pond - have read over the last 30 years that anythink with a KB stamp on the box was perfection.

Has it all changed ?

Are they now producing crap ?????????

 

they are a good choice for the money. Just don't go throwing a blower are nitrous at them

 

From what I have read, they are hypereutectic pistons. Hypereutectic pistons are cast pistons with an added ammount of silicon (if I remember right off the top of my head) to make them lighter.

They still aren't as strong as forged.

 

There has been some controversy over this brand of hypers. When they are pushed to the limit, as allot of enthusiasts do, they will shatter instead of bend like the forged ones do, causing much more damage. KB was first on the market with a hypereutectic piston, their's were the first piston to be installed, their's were the first hyper piston to be abused and break. As far as being strong, the new 7000RPM Corvette Z06 comes with hypereutectic pistons.

 

I'm not sure of the why's for all the negative opinions regarding KB pitons, but I do know that for 383 stoker pistons the oil ring is into the wrist pin, and uses a insert in the wrist pin hole to carry the ring. The engine builders I spoke to didn't like this. Speed Pro Hypers don't have this and I believe they have a better performance record. For non nitrious or blown applications Hypers are great. They are actually stronger then forged, but brittal by comparison. If you plan on any type of forced induction, don't waste your time with Hypers.

 

One of our well known local engine builders won't touch them. Failure rate is to high for high performance engines, per his comment. Fragile tops (seen it first hand), can cause servere engine damage (seen this as well).

Also their ring gaps have to be followed exactly! From my understanding, these aren't a builder friendly piston. I'm on my second crate motor with KB's, and we will see how long this set lasts........jury is still out.

 

i have had great luck with mine

 

As do the rest of the clearances in the engine. If the builder can't do this he surely can't build an engine properly in the first place and you wouldn't want him.

 

This is my only complaint with them, but it is more something borne out of necessity from stroking the engine in the first place, rather than a strength issue. I don't know about small blocks but in a BBC, because of the stroker configuration, if you want to maintain a desirable rod length to stroke ratio it is necessary to cast a piston with the wrist pin 1/4" higher than normal, and this puts the wrist pin into the bottom of the oil control ring groove. I suspect Speed Pro hypers are for standard length rods and this is why the wrist pins don't protrude into the oil ring groove.

 

It's the 6" rod that neccesitates the pin into the ring groove. The stroke to rod length ratio with a 383 is better with 6" rods than 5.7" rods.

 

First some basic history:
Sealed power made the first hyper pistons, and then KB's followed. Both are very good pistons and much better than stock cast in every way. They are inherently more brittle than forged and less than stock cast so are more durable than stock, and only slightly less than forged. They have been used successfully with nitrus and blowers for years if the combo is perfect for the application. Most overdo it so perfect is usually not in play. Most cars have hyper pistons from factory and have for years so theres my proof.
Second is mathmatic certainty:
KB piston moves the top ring closer the crown of the piston for better sealing, so it actually is not more brittle or weak than others just a different design. Moving the ring higher means that the top ring will be running hotter than most other pistons and needs a larger gap (a 350 will be at least .026in as opposed to the .010-.018in for stock). This is overlooked when most builders put rings in and this causes many failures, not the piston. More of the better engine builders use KB before any other brand and have few failures attributed to pistons.
lastly:
High performance engines need to be build with much more attention to detail when checking clearances than a stock rebuild cause the increased load placed on the parts. Most good engine builders are stock rebuilders so they arent used to the extra work and things are overlooked, causing failre rates to rise. Only shops that specialize in performance builds or racing applications have the lower failure rates cause they are used to checking for these clearance issues.

 

Well this is what I meant by maintaining a desirable rod to stroke ratio, and the only way to do that is changing rods as part of the stroking package.

 

The only two vendors around that offered hypers were Federal Mogul and KB in 1996, according to Speed-O-Motive who's mantra is something to the effect of "Stroker experts since nineteen forty something". And KB was the only vendor that had a piston available for a stroked 496ci 6.385" rod big block. This is where I'm getting my info.