The sound : marbles in a can, gravel in a glass jar, etc

When : under heavy load with WOT at 3k plus rpms.

my car: 85, 305, no ecm, 1406 edlebrock (at factory settings) , accell 59107c vac adv distributor (set vac adv per included instructions, new plugs/wires installed as well). Edlebrock performer intake, hedeman headers , 3" exhaust w/ cat, stock block and heads. 8° adv base timing set and rechecked recently. Running cheapest gas I can buy.

Question: I've read several threads on the subject of spark knock, I'm just trying to decide which direction I should go first.

1. Should I change to mid or premium gas? Will this really help or am I making up for a deficiency elsewhere , ex: timing, plugs, tune carb.

2. Should I be tweaking the timing? Do I need to tweak the base or the vac adv timing?

​​​3. Since it's only at WOT and I haven't tuned the carb aside from initial set up, do I need to buy a tune kit? Is it staving for fuel?

4. Is it the plugs them selves I should be looking at? I'm running Delco r45ts plugs.


​​​any help is greatly appreciated as always.
​​​​​​

 

The "total" timing - which is the static (dist body twiddle) plus the centrifugal advance provided by the springs & weights - is too high.

One of those 2 quantities is too great. Either the centrifugal advance needs to be limited, or the static is too advanced.

Ignore any "number" you may have randomly generated using "light" and "mark". Whatever YOU think is "correct", the engine DOES NOT agree. Back off the static timing until the pinging quits. You can try higher octane gas but the car shouldn't really need that. More likely it's simply too much advance.

It's not the vac advance; that only is in effect at high vacuum and high RPMs, i.e., cruising. It goes away at WOT since there is essentially zero vacuum at that time.

Those plugs should be fine, and it's most likely not a fuel mixture problem, unless there are other signs of that at the same time; either thick black smoke (too rich) or thin grey smoke (too lean).

 

Thank you sofa, I remember reading another one of your posts regarding timing. It was an excellent read and I'm glad I can hopefully apply this to my issue.

 

Oh and no other signs of fuel mixture issues, no black smoke, no smoke of any kind. No rich smell

 

Thank you sofa, backing off on the timing worked wonders.

Intial timing check showed me at 10° advance. I know I said 8° in previous comment but I guess it was 10°, dizzy was Rock solid, no way it moved. I was just wrong

Backed off to 8° , went for a test drive , rode it hard and it was 90% better. On one pass up hill I had a breif moment of knock. Back to the shop.

Backed off to 6° , test drive, rode it harder. No marbles or gravel what do ever. Cleared it right up. Then it got dark. I may try going back and splitting hairs at 7° and see if anything changes. But not tonight.

Thank you again sofa.

 

Awesome! You're welcome.