Originally Posted by ss crazy
Someone made the comment that the new 350 LT-1 rods were lighter and stronger than the GM PINK rods. Is this true? If not what would be a safe max rpm range and horsepower amount for a GM steel crank, LT-1 PM rods, and hypertauntic pistons?
I beat to a different drummer, I don't use PM at all and I dont like fracture cap technology.
For a hot street or claimer engines I use these SCAT rods SCR6A and SCR6A7. These are both 6 inch, I beam, 4340 forgings using ARP cap screws with alignment dowels, with a bushed pin end. Both outward pinch the big end mating surface this provides a platform positioned such that it naturally resists the tendency of big ends to deform a high RPMs which reduces if not removes bending loads on the fasteners. These rods will usually clear the crankcase and cam when used on stroker motors without having to grind the rods and/or crankcase for clearance. The difference between them is the shank and outside of the mating surface shape of SCR6A is an as forged item so it costs less, while the SCR6A7 is more conformal configuration (smoother), with a surface polished and shot peened beam section.
For performance engines that will see 6000 RPM and higher I shy away from pressed pins, especially where cast hyper-eutectic pistons are used. Should these become overheated and seize the pin, a pressed-in-the-rod pin will fail the piston resulting in loss of the engine. A floating pin, bushed in the rod provides a third bearing pivot point that runs much cooler than the piston itself and therefore less likely to seize the pin. This does mean you have to buy pistons machined for pin retainers and you have to install the retainers correctly.
I'm always amazed how guys cheap out the rods. This is the highest loaded part in the engine and the most likely point of failure and the failure is almost always catastrophic to the rest of the engine. On a risk matrix where the likelihood of an event occurring and the consequences of the event occurring, failure of a rod in a high output, high RPM engine is at Likely to Almost Certain in Likelihood and Major to Catastrophic in Consequence. So rods and pistons get a really big part of my attention.