They are not bad by design but it is the abuse upon them that causes them to to ofcourse fail. The weight on the crank from the rod and piston is the key factor in stressing the bearing.
As many of you already know the piston is cast with oil passage for coiling. This makes stock piston heavy and with the addition oil it makes an extremly heavy for use at higher power levels. This is also what causes wrist pins to fail.For reference Sunbelt uses stock bearings and has them F1 Coat them. Brian Nutter from Weisco has done alot of testing on stress from different pistons including stock. The results were that you could double the horsepower lvls of the engine and maintain the less stress than the stock rod and piston combination on the crank. Here to summerize what I have found about the 300ZX engine
1) pistons are cast and heavy and simply won't measure up to forged ones
2) The use of hydrolic lifters limit the max RPM to about 7800 RPMS or so with less than favorable results starting as low as 6400 rpms.
3) PCV design is not very track friendly
4) Oil pump design is pretty good but a bigger oil pan would be nice.
5) Turbo manifolds are biggest hinderment for big power
6) the boost piping I also believe to be very restrictive. And I also believe that the biggest hinderment for big power 300ZX is money. The Supra community has big ballers thats all ;-) This just my opinions others may agree or disagree but discussions of these nature are good.
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