I have a 21 ft cruiser. 454 BBC. 10.2:1 calculated compression ratio. 750 vac. Sec. Holley worked over by Performance Carb Shop in Ontario (Ron), Edelbrock Air Gap, MSD 6A and Distributor w/ vac adv locked out all in by 2500 at 32°, 049 heads SS valves next size larger than stock,  Aluminum center rise exhaust manifolds, i cant remember which cam at the moment. 91 octane.

I had a previous issue where blew the head gasket and head cuz I was running too lean. So thats when I had Ron work my carb. Well, I still here that ugly detonation sound around 4500 rpms so i just let off the throttle. But heres where it gets  interesting... my last trip (Halloween) i went from Havasu to the Gorge and made a Uturn when i got to the end of the no wake zone. So by now the engine is pretty cool. Oil pressure is up. So i get on the throttle. Just about to 5000 rpms and I hear nothing. Runs great! After a few minutes of going from 4000 to almost 5000 i hear the detonation so I keep it at 4000 the rest of the trip. What gives? Spoke to Carb Shop cuz i thought maybe Im jyst one jet off. He says NO WAY is it lean at this point. What should I check over the winter? Sorry so winded. Tried to give as much info as I could. Thanks for any input.

No. I never checked plugs.

No. I never checked plugs.

Pull a plug and post a picture.
What's your water temp run at?

I will have to ask the machine shop. Is one preffered over the other Joe?

Hmmm... ^^^

I will have to ask the machine shop. Is one preffered over the other Joe?

Not necessarily.  Only testing will tell for sure.

Most cams are recommended to be installed 4-degrees advanced.  Some cams are ground with advance built in, not necessitating an adjustable timing set. 

Advancing your cam increases cylinder pressure because more air/fuel mixture is trapped in the cylinder when the intake valve closes earlier while the piston is lower in its stroke.  A cam with shorter duration has the same affect.

I seem to recall that you selected a relatively short duration cam, which would build good cylinder pressure.  I think it was a good choice for your style of boating, but I think your dynamic compression ended up a bit high.  I also think your heads and intake should produce good flow velocity enhancing your effective compression ratio, building a lot of cylinder pressure at the peak torque RPM.

Do you know if your block was zero-decked?  If the quench distance is too wide, it can cause the engine to be detonation prone.  If your block is not decked, your pistons will be ~.020" (deck height) in the hole.  Your quench distance will be your head gasket thickness plus the deck height.  Anything over .055" is bad news in a NA deal.

Just some thoughts,

Joe

One last thing.  What spark plugs and where are they gapped?

It is no zero decked. I dont recall what it is. But when i measured it and used the number to calculate my CR with .051 thick gasket and 117 CCs, I came up with 10.2:1

Carb guy says thats not so high. He tests them at 15 PSI

Cam is installed straight up

No disrespect to anyone but if we dont know if the balancer is even accurate,  or what a spark plug looks like its really hard to diagnose the problem without ruling out the basics... it could be lean as fuck!!! Imho...it shouldnt have a vac sec 750 on it to begin with... but we've been thru that already on another one of your threads about carbs n tuning..it seems you want everyones advise but you never take it and you keep having problems... just my. 02.. best of luck sir sorting this out...

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I intend to get a new balancer, check tdc, re time it, go out and run it and pull the plugs and take some pics.

Update... so I gave my boat a tune up; MSD cap and rotor, replaced the fuel pump with a new Clay Smith mech unit (it leaked), r42 ac plugs and a new Summit balancer. The cap and rotor was used but looked good. The fuel pump was a Pro Comp deal which always made me nervous. I ran r44 plugs but wanted a colder plug. And the balancer was a used unit which looked questionable. Took the boat out with all those changes to Havasu this weekend. IT RAN GREAT!! I was having what i believed to be a detonation issue before these changes. I had a good feeling when i checked timing at 2500 RPM and saw that it was now way off. I now have timing set at 33° and i'm confident it is accurate. It was such a great feeling running that boat all the way to 5k with no funny noises and running like a beast (to me)! Just want to say thanks to all who chimed in whenever I had a question. I really appreciate it!!!