How does Power Reliability Threshhold work?

So here I have two values for Power Reliability Threshold. According to the material used for the block, it should be 771.65, but according to the engine in question it is 405. As this was a cloned family that was originally an inline-4, I thought it might be a holdover from that. So, I changed it to an I6 and an I4 to see if it recalculated properly, but then it gave me 303 for the I6 and 202 for the I4, indicating that 405 is the real value for this engine. So how exactly is PRT calculated for a given engine?

The pistons also might not hold up, try switching to heavy forged or something and it should surpass the block power, leading to the block being the limiting factor.

So not only can your pistons explode from too much rpm, or too much torque now it’s also too much power(?). Just something to be aware of.


I think the block value is the maximum PRT attainable with that material. 405hp may be from other internal components.

Yeah, I’ve observed it a bit and it’s like @Riley says, although I’ll add one thing - the limits for both the block and the pistons are not constant for the given family. If you change the bore, both of those change too. Block’s limit decreases with larger bore, pistons’ limit increases. I think that pistons in general have the power limit proportional to the torque limit, so that’s easier to track (but I didn’t check that exactly).

IMO it makes perfect sense for both of those having their power limits (and IMO the head should have one too), since they are the walls of the combustion chamber, directly in contact with all the pressure and heat produced there.