Rage

What is the structural hp limit for the stock Mercruiser 496HO cast aluminum piston in a naturarly aspirated engine configuration assuming no detonation and rpm's at 5400 and no piston to valve clearance issues? In other words just what hp can this piston handle disregarding all the other potential causes for piston failure?

Rage

Anyone?

LAKESIDE RESTORATIONS

What are you looking to do? I dont actually know the "engineered limit" off of the top of my head.. However I know that after around the 500-600hp limit piston swaps should be considered.. The Hypertectic pistons are pretty strong, they just cannot tolerate the heat from possible inaccuracies in fuel delivery caused by some modifications as well as the forged ones can..

For example This is one of the reasons that Procharger does not offer a kit for the newer 496's over the counter.. The fuel delivery with that kit would not really be precise enough, along with some other reasons.. Where as whipple's base kit is more precise due to the reprograming of the engine's ecm and useage of a different injection system.. Even with the whipple kit there are other upgrades that should still be done to that application, but the whipple is a safer bet on longevity..

The other option for those that dont want boost is Raylar's kits. If my memory serves me correctly the recomendations of different pistons on his kits are after about 500-600 hp range as well (except with some certain parts).. Raylars components build power because they operate more efficently than the stock parts, especially when the Ecm reflash is done in conjunction with the cam, head & intake swap..

If you are only doing soome moderate alterations, your stock pistons should be fine. If you are going for big power then consider a set of forged.. Jamie

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Plane Silly

I recently did a Raylar kit to a buddies boat with some not so good results (not Raylars fault). It ran great for about 40 hours and then broke the edge off of a piston. We set it up with an air/fuel ratio meter with cruise rpm being around 13.5:1 which had wot around 12.8:1. And you guessed it, it failed at cruise.
With the right (conservative) tune there shouldn't be a problem. But if you put it on the edge the weak link is the pistons.
By the way, the motor now has forged piston, rods and few other goodies

Hot 4 Teacher

Rage, you're about 525 hp if I recall correctly, right? I was about the same when she did this:

Hot 4 Teacher

Now, she's been bored 30 over with forged internals and looks like this: Thanks to BES (Bischoff racing) and blowncrown! Do those risers look familiar to you? lol.

Rage

Yep, they sure do look familiar....only much better!

The reason for my question is that I am likely in the 550hp range now and considering additional upgrades that will likely bring me to the 580+hp, maybe more, naturally aspirated. Or maybe not since no guarantees with DIY. But in any case before I do that I want to make sure that this is not a recipe for disaster. I have a complete handle on the A/F for each individual cylinder throughout the rpm range and I will keep it in the safe zone to insure no detonation. But if the added hp alone could cause a failure the result would be the same... a ruined engine.

So my question is purely hp related. What hp can the stock pistons safely run with? Actually the same question with regard to the stock rods, crank and bearings as well.

Hot 4 Teacher

I see. In that case, I haven't the answer, but I'm sure Ray and Tyler Crocket both do. Once you do your thing, please shoot me a PM or email and share your new found secret for more hp.

Rage

Anyone else with info on this subject?

Raylar

Rage:

I know you are waiting for me on this subject. My feeling is that everything is running perfect on a 496 that the stock cast piston with its full float pin can probably take 600-625 HP flywheel engine horsepower. The problem comes that were not in a perfect world and in the marine enviroment engines suffer from "RAYS LAW" which is that "Murphy was a f***ing
optomist". With poor fuel quality, high air temperatures and the LOUSY combustion chamber, bore overhang of the stock GM iron (mistake) heads, the chance for detonation and uneven cylinder combustion temperatures in the chamber on top of the piston, the rpms of lets say 5200-5300 rpm required for 600HP plus will result it a high potential of piston failure, which almost always occurs around the edge of the valve relief in the stock GM piston, where the top material on the piston is only about .090" thick max!

Love to see the dyno sheet for your 550HP iron head, stock manifold engine. You would be the first engine builder in the world to achieve those results with just all factory stock parts.
Back in 2001-2002 Innovation got to 525HP with seriously reworked iron heads, a to big for clean idle cam and some trick pistons made for them by GM. How many hours now on your "suped up" 496 and are you running at normal UTAH elevations?
My advise if your looking for more than 500HP with stock iron heads is change the pistons to forged units, because when the non-siamised thin wall casting of the 496 block losses a piston, about 6 out of 10 times you loose the block and adjacent parts like crank and rods, which is a very expensive proposition to replace.

Good Luck!

Regards,
Ray @ Raylar