Anybody measure KB hyper pistons? Typical Undersize?

Typically...how much under standard bore sizes is a KB hyper piston typically? I know you have to measure the actual pistons used, but do they usually run .0015 or ? under the std bore sizes?(Std, +.030, +,.040, +.060, etc).

Is there a rule of thumb?

Most pistons are under the size of the bores, not as big as the bore so the machine shops have to make the bore over size I've never ran the KB hypers, I don't like any cast pistons I have ran and used thier forged pistons They had the clearances built into the pistons

Hi, they are supposed to be appx .0015-.002 under when measured at the lower part of the skirt. However, if measured just below the oilring it is closer to .003-.004" so they are not that different from other pistons. Used KB pistons tend to have more clearance at the lowest skirt point, often .002"-.003" more than should. The skirt edges are kinda weak. If you try to straighten back they can easily break (I have tried!). I am not sure if they make more noise when worn, if the skirts are long as for a typical 440 piston.

Just measured some Wednesday night. They were all .002 under. This is much better than the last 2 brands I measured which had .0015 variance between them.

Good info guys...thanks for confirming that.

I have a set of kb .30 over hypereutetic pistons on my 383, absolutely silent even at the upper limit of the clearance.

V8punch...how much piston clearance did you run?

My kb hypers have .007 piston to wall clearance. They dont make a sound, nor do they use a drop of oil. That clearance wasnt the goal, they were pistons from another engine, and after honing the block with a plate thats where the clearances came out, so I rolled with it.

I did this engine 4 years ago, I do not remember, probably at the upper limit specified by the manufacturer.

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Typically...how much under standard bore sizes is a KB hyper piston typically? I know you have to measure the actual pistons used, but do they usually run .0015 or ? under the std bore sizes?(Std, +.030, +,.040, +.060, etc).

Is there a rule of thumb?

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They are tight because the pistons dont grow much. But the clearance is determined by bore diameter and intended performance. But still its a very tight perimeter.

.0015 to .0055 from small bore NA to large bore supercharged.

The clearance is measured at the skirt parallel to the balance pad height.

Whats even more important IMO, is the top ring gap. As it is closer to the top of the piston vs other type pistons that it requires extra top ring gap to prevent butting of the ends.

Example, NA 4.36 bore race gasoline motor = .033 top ring gap.