Had my 455 set at 9° with the vacume advance disconnected and it detonated and rattled when I shut it off, so I backed it down to 7° and it's still doing it. Any ideas? Running Ca gas,91 octane, unplugged the advance 850 RPM with a stock style electronic distributer and I can't drive it for fear I'll kill it. Would it be this shitty Ca ethanol gas even thou its 91 octane?

 

It rattles when you shut it off?
What are the build specs?

 

Build specs would be nice. What distributor is in it? Is it possible you're getting a bunch of mechanical advance in at idle?

By rattling at shut off do you mean dieseling? Be as specific as you can - there are a bunch of different variables that factor into the ignition system alone.

 

What idle speed are you running?.

Roger.

 

Turn down your idle, 850 is too high. Either that of shut it down in drive if you are running an automatic.

 

Higher initial timing will help with the dieseling, as well as give you better throttle response.