What is the deal with these pistons? Do they have different expansion rates? I notice the distance from the ring to the top of piston is only about 1/8" in the spot where it broke.

 

I think that is why they break. They are very thin at the top and are ribbed. This is the third time I have seen this exact thing happen with the KB's. Seems like a design flaw and they havent resolved it. The first one I seen do this was about 5 years ago.

 

There is a possibility that the piston manufacturer cut the grooves with too sharp a break at the bottom of the groove cuts. If there isn't a smooth radius on those fillets (even though they are only .010-.015"), that can start a stress riser and end up propagating a crack. If you (or the engine builder) still have the offending piston(s), have him look at the bottom of the upper ring groove and see if it is rough or sharp. If so, call the piston maker and hit him up for some ca$h.

 

Any thoughts on why #2 would break twice? Possible head issues causing too much heat in that cylinder?

 

inaudible detonation. caused by too lean or crappy gas. cruise at 4000 has power valve closed, so it runs lean as it should. crappy piston fails in leanest cyl. forged will fix that. even so i'd run 2-4 degrees less timing in #2 (washers under spark plug).

 

QFT - friend took his big block to local performance machine shop.. they had the same reaction...dont use these KB hyperute pistons...the guy then went on like a 5 minute rant on what Crap they were and how many customers have had problems with them.

The end result was you want to use these pistons...find another shop..Apparantly these things fail so often that machine shops are getting bad reps from them.

BTW they had good things to say about the Sealed Power ones

 

any possibilities of a cam screw up, and or a valve problem hitting the side of that leading edge and popping it up?
if all things are equal or the same, there has to be a reason for it being the same cylinder

 

What does this mean?

BigBlockk

Later.....

 

Internal cylinder timing? Years ago we were told to run 4 standard type plugs and 4 side electrode plugs(sorta like a boat motor plug)because in the L-88 it would produce 30 more horsepower with 4 of the cylinders running several degrees more advanced timing.I dont remember what cylinders got the boat plugs.

 

I agree !!!

 

Look, this is just my .02$. The problem is clearly related to one cylinder and apparently on the larger intake valve side. In the books of D. Vizard I once read that a valve spring surge could already take place at around 4500 -5000 rpm. My guess is that this spring is weaker than the rest and if the valve to piston clearance is already at minimum this could make the valve hit the piston.

 

That is as good a theory as anyone else's. If you had the damaged piston and the broken section to look at, you could examine how it failed and get a pretty good idea of the cause. And, yes, there is more stress on that piston (cylinder #2) for some reason; detonation, valve float, tight bore, cylinder ridge, etc, or a combination of issues. But the piston is breaking and it is part of the problem as well (weak design or poor manufacturing).

 

I've never heard of changing individual cylinder timing with different style plugs. How would this work?

 

I'm not exactly sure but the way I remember it is the deeper in the cylinder the electrode the more advanced and the further away the electrode the more retarded.Hopefuly some of these racers willl chime in and tell us if this is bull or if that was good for old head designs and today thats out dated.Maybe the new ignition systems take care of this.

 

I imagine it has to do with the burn rate. The nearer the plug to the charge, the faster the burn. Probably dealing with a degree or less retardation (small potatos for us street folk). You'd probably have to be in the high-end racing business to notice anything different.

 

never heard of that one either; seems like indexing and heat range would make more difference. never heard of intentionally having different heat range plugs in the same engine at the same time to get more power either. i think most agree that even indexing is a little over the top for a real street engine. 0.02

 

You'd be amazed at what they do with race engines. Even the cam will have several different profiles for intake and exhaust to acct for various flow amounts into cylinders. There are also varying compression ratios in same motor, different header tube sizes etc etc to create the optimum curve for whatever they are doing.

So many spend so much time making everything as identical as possible, yet the serious racers often intentionally mismatch things.

Fun stuff!

JIM

 

Just as a point of discussion... I'd bet that the little nuances the "Big Boys" do to their engines are all "adjustments" to compensate for an engine design which is NOT uniform in its operation [cylinder to cylinder]. The flow characteristics of each runner in an intake manifold are not identical. Their little tricks are likely attempts to get really uniform performance behavior out of that imperfect hardware.

 

Exactly...none of these engines are uniform in dynamic running conditions. They spend the time to make changes and test to try and equalize the *tune* so to speak. That tune can easily be varying compression ratios or timing events, runner sizes etc.

I know of a small block Ford race motor using a Victor intake due to rules. Now this is a 9000 rpm type deal. When all was said and done, the entire wall of the intake was welded up over a 1/4" on the two *rear* runners and then ported to achieve flow numbers on line with the other runners. The cross section of the modified runners is huge in comparison. But it picked up 30 HP!! The neat part is you would never know it was done...lots of disguise work!

The old Edelbrock tunnel rams for BBC's had different sized runners to make up for the *good port* and the *bad port* in big block heads. I can tell you that my heads have entirely two different valve jobs on the respective cylinders to help accomplish same thing. While most folks are happy to achieve a 5% variation in flow on BBC heads, mine have been massaged to within 5 CFM!!

You will also find MSD controls with individual cylinder timing available.

All that is neat stuff....but in this case, I think we just have a motor with Hyper's that ran into detonation...maybe even mild....for a period of time and they just can't take it. Similar pictures are all over the web.

Get forged pistons and then really work on the tune.


JIM

 

I think you guys are taking it to far.