Hi,



I pulled my #1 plug from my stroked 340. I have not learned the art of reading plugs. The porcelain appears to have chipped off on one side of the plug. I think that is indicative of detonation; but I haven't heard any rattle or ping (means nothing). The plugs are Autolite 64's.

https://drive.google.com/file/d/15R7gOsiHDfcLlziLcsJYAa1f0qF0jXW8/view?usp=sharing

https://drive.google.com/file/d/15X6JF_Ls3pw8PNM9XuHqk_3mki3e09HF/view?usp=sharing

https://drive.google.com/file/d/15WXBwJnwwYXbtvrHfXDCLO8ZvD7N-2rm/view?usp=sharing

TYiA!

Looks more like some nasty additives coating your plugs and that;s what's chipping off. What are you running for fuel?

What fuel are you running ?

The porclyn is NOT chipping off, it is chemical deposits from combustion that you are seeing chipping off
What type of heads (aluminum or iron)and compression are you running?
You might want to try a #65 plug in your motor to see if that hotter plug will burn hot enough to prevent those deposits

Hello,

I have been using Exxon/Mobil Synergy Supreme premium gasoline mixed with about 5 gallons of Sunoco 260 (100 octane).

https://www.exxon.com/en/synergy-supreme-plus

https://www.sunocoracefuels.com/fuel/260-gt

Adding the 260 really helps with fuel boil.


About the car, '68 Barracuda FB Formula S, 3.91's, 5 speed manual, DLI ported X heads, M1 intake, holley carb, mech roller cam (about 248@50), about 9.7:1 compression ratio, bored and stroked to about 386ci. Timing is 22 degrees initial, 37 total all in at 2500. Vacuum advance adds about 8 degrees of advance. This engine likes a lot of advance, meaning I could probably go with a little more initial and total (2-3 degrees). Maybe it wants more timing to burn off some of the deposits?

Cab's suggestion of a hotter plug is interesting; I could give it a try and listen carefully for ping/rattle.

If you need any additional info, please ask.

What pump gas are you guys running in your cruisers with carbs?

The race fuel is making the deposits on your plugs, at that compression ratio and any altitude above 4500 you don't need any fuel additive or race fuels
Based on how much total timing your running I'm assuming your above 5000 FT altitude, correct?
On your deal I would change to the #65 Autolites with no other tuning changes other than dropping the race gas to your tank
I use to help several NHRA stock class racers that ran 340 motors, one ended up setting the E/SA record that stood for two years, later on he held the C/SA record with a Challenger I sold him that he made into a 340 6 pack T/A clone car, that car was a rocket ship None of those Stocker motors, 1970 4 barrel, 1970 six pack and the1971 340 four barrel motors like more than 33 degree total at the track or on the engine dyno under 4000 Ft altitude in SO CA
IHTHs

I think this plug has oil contamination on it, as indicated by the shiny and crusty deposits; please confirm:

https://drive.google.com/file/d/17cxPxlG9T3D6jL7VeWem-VuHjm-Gmbta/view?usp=sharing

Maybe, what does it smell like? oil or gas? If it's still looking that that the next morning then yeah I'd say it was oil

Man, that dude is nasty, fix the problems and that motor should wake up a bunch of power
It looks like oil and maybe to rich also. have you done a leak down or compression test on the motor? If so what where the results? If not try and do that next