Does anyone know if there is a way to read a spark plug to confirm detonation? I am unfortunately getting a rattle under acceleration with my new 455

Its pretty loud. I have my vac advance hooked up. 52 degrees all in

9.5:1 with iron heads
228 @ .050 duration
870 Holley carb with vac secondary

I am using ported vacuum.

It turns out that I was at 36 mechanical when I was at 52 with vacuum advance.

I turned it back to 31 mechanical and took it for a ride with vacuums advance plugged. The rattle was still there but not as loud.

Then I plugged in the vacuum advance and repeated driving conditions. The rattle is the same as when the vacuum advance was plugged. I just timed it again with the vacuum adavance all in and I’m reading 50 degrees.

I am running ACDELCO 4#45S plugs

Using a stock HEI. Total timing is coming in around 2500. I am using Shell 91 octane. I am in California.

I am on a test drive again with a third adjustment. I set the timing back further.

With the vacuum canister plug I’m getting 13 initial and 28 all in. With this setting I’m getting 42 all in with the canister connected.

I am still hearing some rattle but its almost gone.

At least I think it’s pinging. Don’t want to rule out something like exhaust vibrating on the body or something.

So I thought reading the plug would tell me if it’s in fact pinging. But the sound seems to be going away as I take out timing.

The first time around I had a puff of smoke coming out of the breather accompanied by the sound. I saw this since I have no hood. I really had my foot in it in 3rd gear under load when I saw this.

Rebuilt only 25 miles ago. I think it was in fact pinging . I just got back from a test drive. And the sound is gone.

91 octane is the best I can get here in California.

I assembled the engine and selected all of the parts.

Cam was degreed and all clearances measured.
Trans is a TH350 with a TCI 2600 stall and shift kit.

Do all your tuning with the vacuum advance unplugged. You might want to put some heavier springs on the weights to delay full advance. Once you have your initial and centrifugal advance dialed in, then work on the vacuum advance. You will most likely have to limit the vacuum advance with some small screws, or ideally get a adjustable vacuum advance canister from Accel or Crane. It includes a small cam that mechanically limits how much advance the canister adds. You need to remember, every time you change the advance limit cam, you need to reset the base timing. The cam changes the base position of the pole piece, that changes intitial timing. There are detailed instructions in the vaccine advance kit that explains all this much better than I can here.

Whatever you do, once you have the timing dialed in with the advance unhooked, don’t change the initial timing to get rid of pinging with the advance hooked up. Make sure the advance in connected to manifold vacuum. A little pinging under mild acceleration, but the pinging should go away once you add more throttle and manifold vacuum falls off.

Ive never played with any fuel additives. And I hear the ethanol in California’s fuel isn’t helping the cause either

I will be ordering an adjustable vacuum canister tonight. Also ordering a wideband sensor and gauge.

I might be lean then. Which explains post number #4. There was just as much rattle with the canister connected at 31 total as there was with the canister disconnected. Since vacuum is zero at WOT, anyway, and I did the test at WOT both ways.

Wideband and adjustable canister are on the way.