lexcrob wrote:In other words if you DO NOT ALLOW DETONATION what so ever and have extreme provisions against it to protect your "balsa wood pistons" your better off than the guy that just slaps in some forged pistons!
Im aware forged pistons intent is to be stronger giving you more room for error or problems. Im just trying to say their often used in applications where cast units would be fine. Now I have no idea how to explain the next weakest link as for as the ka engine. I believe i heard rod bearing failure is next on the pecking order.
*so say someone wanted to break 500hp arp rod studs "stretch torqued" and lower compression pistons would help get you closer than just forged pistons. AND KNOCK PREVENTATIVE AND DETECTION OUTMOST IMPORTANCE! OBVIOUSLY
When engineers choose a material for an application, there is a factor of safety they use to account for imperfections that they can't control or are too costly to control (cheaper to build less perfect parts with more material than to try and get more perfect materials and reduce the material needed). As a result, there is usually some room for adding power without failure, but it depends on how big of a factor of safety they use against how imperfect (in terms of crystal and grain structure) your particular set of pistons might be. In short, there is a bit of a gamble where your odds start to stack against you the more power you try to make.
Certainly, lowering the CR helps control detonation, but I don't think we have much statistical data that could be used to determine if lowering the compression (using same material as stock pistons) can be enough to allow the engine to stay in one piece @500whp. I tend to think rod failure will occur before then (from what I recall of a few examples of failures where detonation did not occur), and I'm not aware of any specific examples of anyone using stockish pistons of lower CR, let alone enough of them to come up with any statistical average of when such a piston might fail. One could try and make an analytical determination, but unless we have a lot of the engineering data, its unlikely we can make such a determination.
As sD stated, analyzing all potential points of failure is necessary. There is some factor of safety for every part, but if you start to add more power, your level of risk increases all around. In terms of the parts you mentioned, I'm not sure rod studs would be first on the list. Rod bolts/studs are under the heaviest loads under tension When the rod sees compressive loads, the combustion energy is transferred to the crankshaft). And tensile loads do not increase with more power (unless you increase engine RPMs) since the highest tensile load is going to occur as you reach TDC on the exhaust stroke. Lower CR, while may be a valid argument is a little bit impractical. Why pay money for lower CR pistons when you might invest a bit more and get forged pistons instead? Not even sure what kind of availability there is for lower CR pistons for the KA. And I would not feel comfortable having material removed to lower the CR either. I understand your argument, and I don't necessarily disagree with you, but from a practical standpoint, there is little reason to invest too much time in them.
And cheers, there is a reason I always loved the KA-T forum. These kinds of discussions are always a lot of fun even though, I haven't tinkered with a KA since 2004.