i have a 355 with 11.1 compression,itr was detonating,unhooking the vaccume advance fixed the problem but cost me some power,a freind suggested a msd chip in the distributer,installed it and now i have detonation again in 3rd at wot,i have already added 5 gallons of 110 octane race gas and some 7point octane booster,i have the timing set at 0,I really need some help,anyone?

 

The compression ratio is just too high for maximum power output on street pump gas. Its going to detonate at WOT and optimized timing. You'll either have to buy better high octane gas or lower the compression ratio.
But here are some things to check.

Check the total mechanical advance timing at high rpm.
should be 32 to 36 deg with the vacuum advance disconnected.
Get an advance timing light or a balancer timing tape to allow this
total timing check.
Because you have too much compression you may have to retard this setting to a less than optimum setting (26 to 28deg) to avoid detonation. This is a crutch, but will get you by.

Setting the total timing acurately is a nessessity, setting idle timing is not good enough.

Get some non projected tip cool(er) heat range sparkplugs.
Stock hot plugs are fine for a low compression low performance motor. A high compression , high output motor needs a cooler plug
to avoid over heating the plug tip caueing preignition, and knocking.

Be sure the carb is jetted rich enough. Being jetted a little on the rich side will help cool the combustion chamber at WOT helping to avoid detonation.
Be sure the fuel pump can supply enough fuel at WOT.
Remember, lean is bad.

What is the carb model number and jetting?
What is the total timing setting?
What is the sparkplug #?

Here's something that does work....

Consider adding a water/alcohol injection system.
Water injection works on high compression motors just as good as on turbo motors at suppressing detonation.
Do a search on the net for water injection and detonation.

Any windshield washer fluid with water and methanol and no detergent or teflon etc. will work great as a anti-detonation fluid.
usually its the generic cheap blue stuff for winter driving.

Water injection will allow maximum optimized full power timing to be used, make maximum power without detonation.

It can also be used under part throttle cruise if the motor pings while cruising. (works simular to EGR at reducing peak combustion chamber temps, reducing pinging and allowing more optimized ignition timing.)

This is much cheaper than a rebuild caused by a engine damaged from detonation.
No rocket science, just simple physics... it works well.
When properly set up a water injection system can easily bring a detonating 11:1 compression ratio motor back under control with improved performance and engine life without needing to use expensive race gas or little cans of octane booster.

The trick to a successful water injection system is being able to adjust the amount of water flow and have a check valve inline to avoid fluid flow from suction/sifoning when the motor is off.

A nitrous oxide systems' fuel solenoid used inline accomplishes this safety concern.
Other than that the systems for naturely aspirated motors are not that complicated.

 

Well i spent all day messing with it,i found by turning the fuel screws on the edelbrock 600 a half turn further out that it totally fixed the problem but took away alot of power,right now they are 1/4 turn farther and it runs good,no detonantion but if i floor it it just bogs =( i guess its just a tuning thing,im going to invest inbetter plugs too.