66 gto engine is rataling and pinging when under load

[666 gto]

[cudaman]

First, remove the vacuum advance hose end from the distributor vacuum canister and plug it (a golf tee works well as a plug).  Then install a dial-back timing light and confirm that the initial advance is where you want it at Idle.

 

Then, have a helper accelerate the engine until the mechanical timing advance maxes out while you watch.  Adjust the dial-back on the timing light to determine the maximum mechanical advance.  Check your manual for the correct specs for initial and total mechanical timing and adjust the distributor position as needed.

 

Once you have confirmed the correct mechanical advance and total timing with no vacuum, try driving the car (still with the vacuum advance disconnected).  If the part throttle pinging under load is gone, buy and install an adjustable vacuum canister for your distributor and adjust it to provide the maximum vacuum advance you can get away with without pinging.

 

You want to run vacuum advance on the street if you can.  Otherwise, your fuel economy will suffer and the car will be sluggish at throttle tip-in from Idle.

[EmTee]

12 minutes ago, cudaman said:

Once you have confirmed the correct mechanical advance...

I don't know the history, but it was common back in the late '60s and '70s to install aftermarket mechanical flyweights and/or springs to increase the total advance and or rate of advance.  This distributor may have non-stock weights or springs.  Measuring the total mechanical advance as described above and comparing against the factory specs will determine what you have in your distributor.

[Pfeil]

8 hours ago, EmTee said:

I don't know the history, but it was common back in the late '60s and '70s to install aftermarket mechanical flyweights and/or springs to increase the total advance and or rate of advance.  This distributor may have non-stock weights or springs.  Measuring the total mechanical advance as described above and comparing against the factory specs will determine what you have in your distributor.

That's right. You want to be all in mechanical at 2100 rpm, 36 degrees 400" and smaller and 34 degrees for 421-428-455.

[666 gto]

thank you for advice iread that low octane i.e unleaded fuel also a vacume leak can also be cause tri carb maifold does have a leak needs new gasket and also would a new dizzy.  help cause the rattle sounds like dissy engine only has 22.000 original miles msd or hdi what woud be better thank you for your help

 

[EmTee]

Fix the manifold vacuum leak first.  These cars ran well with the original points distributor.  When working on classic cars, I like to follow the Hippocratic Oath and "do no harm".  Once it is running properly with the stock ignition you can consider 'upgrades'.  Changing to a later Pontiac HEI distributor is one option, however, note that even though that would use factory parts, the distributor advance curve would still need to be checked to make sure it's appropriate for the GTO.