Rage

Ray,

What is the HP limit for the 496 stock cast aluminum Mercruiser/GM pistons in the 5200 - 5400 rpm range and 150 psi compression (assuming no detonation)?

Rage

I have been told that the stock 496 cast aluminum pistons will gernade at 550 hp alone. Any truth to this?

Raylar

I don't know if the HP limit of a 496 stock hypereutectic piston can be determined exactly. It has been our expierence that if everything is right with a stock 496 that in some cases with superchargers there are a few boaters out there pushing 625HP in the perfect setup for now.
We have determined that we do not want to use the stock hypereutectic piston and rod above 575HP because we know that is the limit for a low lift cam that the stock piston will accept. The stock rod bolts are not large enough for power much beyond that level and thats all the horsepower we can make with our 525 kit and headers on a stock 496. So the use of the stock pistons for Raylar ends there. As any stock cast piston there are exceptions to the general rule but the piston is not inherently weak, it just does not like detonation, including detonation with boost from supercharging. I know of many 496's in commercial use where engine hours of over 2000 hours have been the case with stock pistons!
As with all hypereutectic cast pistons, they are a bit brittle and when they fail they tend to come apart quickly in a bunch of pieces and sometimes the block fails with the out of control connecting rod bashing around.
Forged pistons, such as the Raylar/Mahle pistons we use on 600HP+ 496's , are always a great deal stronger than cast in a higher horsepower use but even forged pistons can fail when subjected to extremely high horsepower loads, detonation, lean burn and other mechanical issues.
The stock 496 is by far the best big block to come from GM in terms of making over 500HP reliably with stock cast pistons.

Regards,

Ray @ Raylar

Rage

Thanks for your always thouough answer.

Best Regards,

Bill