teezer

never been in one of these motors but seen alot of engine explosions over the years

my guess is the exhaust head separated from the stem first, that valve head really took a beating on all angles and finally did the piston in ~~~ if you look at this piston tops and the relief in the center, that valve bounced around in there till it broke the center of the piston (thinest part) ~~~ and at WOT unattached pieces go to the least resistance

my other guess is the exhaust valves are 2 piece construction, and the joining area failed

Exotic-metal55

Ok, it seems the general opinion is, that the exh valve helped the piston break into peices and make a 55 into a glorified rock tumbler.

What catastrophic event weakened the exh valve? They are hollow stemmed and sodium filed.

What damage started the blow-by on two previous WOT runs? The damage had started and the next run it all went.

I want to make sure that I do not repeat this event or any others?

Havoc

Are all 55's exhaust valves sodium filled? I thought only the SLR's had sodium filled exhaust valves...

Rouven036

i faced two times the problem of a gone y-pipe support ring (in the rubber hoses between airfilter housing and throttle body is a metall support ring integrated, to beware the hose of getting bend under high intake air velocity) with a similar result. if the airfilter isn"t removed or installed with great care, the ring could be bend and as a result it, ther ring may fall out and getting sucked towards the throttle body. now during wot the ring fits thrue the throttle body and will cause some damage and a lot of splinters on the supercharger rotors. these chips are also able to pass the fine intercooler channels and will reach now the intake ports and zylinders.
in one case i faced, only the cylinders where seized, on the other nearly same damage as on your engine happend (exhaust valve broke (stucked because of metal chips) and piston damaged, not completly gone like on your engine.

Flight Test

I had very similar thing happen to my old corvette. It ended up being a throttle body blade screw had backed out of the throttle body and made its way to the #8 cylinder.

Exotic-metal55

knowing about the bellows rings , is great info. I have and have had the 80mm bellows from the 08 sl55. I just pulled the bellows off again to triple check the rings inside. They are still there and not loose or missing .

The newer -larger bellows seem to really have the rings molded well inside the bellows.


I am not sure about that. I can see the insdie of the valve stem on the broken #8 and it is hollow.