You were lean, you had a loose intake manifold, your timing was too far advanced, you ran it hard, consider yourself lucky thats all you tore up..... Time to pay the nice man holding the shiny wrench who is shaking his head and thanking you for your business.

I see a 383 stroker assembly in store. Smile smile.

I don't agree with the 32* being too advanced, unless the stock Vortec dinky cam and decent compression.

Experiences may vary.

I ran a 355 with flat top 4 valve relief Pistons, vortec heads, comp xtreme marine 262h cam. I ran it at 31* all in. I got a ton of hours on it.

Detonation is caused by
lean, lack of fuel for some reason
too much timing
octane to low and or too high of compression
hot water temp
hot intake air temp

pick three,lol.i will go with 1 2 and a little of 4 caused from the detonation.

I've come across articles in the past I read for some reason or another and most articles/forum post seem to be btwn 30/32 total. I never dug into why however those total advance numbers would always seem to pop up. Does it make sense to me without researching it. NO. Are the combustion chamber on those designed differently that makes some magic prespark or something? Only vortec heads I've run were/are on gm trucks with 89 octane. I'm not agreeing or disagreeing with anyone on the subject rather curious.

I ran a 350 with a hot cam and forged flat tops. Had a 650 demon on it. 32* total timing and it was all in by 2500 rpm. Ran a 21 mirage on a 1.65 ratio drive. Turned around 5600 rpm. Never had a minutes trouble except for the occasional broken Alpha. Same engine is still running in my buddies boat today.

Yeah, think I pretty much copied your build when I was researching what to do when my 305 bit the dust. You and a couple others on here were running similar setups. Dual plane intake also.

Previous photos of the heads were after a little cleaning and a couple passes with a surfacing stone to knock the carbon off. Here's one untouched except for a quick wipe with a rag. Didn't do anything but stick to the carbon and make it whitish.



Here are plugs 2, 4 6, & 8, in order...



And 7, 5, 3, 1 in that order...



And here are the piston tops, untouched...




And, yes, I will check the head surface. Just need to track down my straight edge and feelers.