Steve40th396

93 Corvette with More Performance 396 LT1, 11.1 TO 1 comp, low tension oils rings, (it was installed that way)236 duration cam, Delteq ignition, ngk tr55 3951s gapped at .040.
Ran it today for 500 miles, long day.
Initially had some light vibration, till I refilled with 93 octane, Sunoco. Same stuff I always use.
Then it went away, ran smooth.
Came home, pulled a couple random plugs. Thoughts? One heat range cooler maybe.

Injuneer

What is the gap now? How many miles? Sounds like you may have had a tank of bad (lower octane) gas. One thing I really liked about running a Scanmaster full time on my dash, was watching for knock retard. Sometimes the gas just didn’t measure up. Adding some better fuel, or even octane boost would clear things up. And I always bought Sunoco when they still carried 94.

Surprised you weren’t already running a TR6.

I like the NGK plug appeared chart:

https://ngksparkplugs.com/en/resources/read-spark-plug

Steve40th396

Gap is at 40. They have about 2000 miles on them.
I have never experienced bad gas, very fortunate..
The 3951s usually looked well.
I havent ran TR6's in a long time. Different engine though when I did. Think TR6s will help?
Their site has the gap at .050. Maybe I should run that too.

Injuneer

Toss up TR6 vs. TR55. What is the compression ratio? What is the LSA on the cam?

For only 2,000 miles the top picture almost appear to be overheating. Bottom picture appears a bit fouled. I would give serious consideration of a TR6IX (iridium). Keep the gap at 0.040. The iridium plugs are expensive. Maybe run a set of conventional TR6 @ 0.040 to see if they improve the appearance. If they do, spend the money for the iridium, and don't worry about replacing them every 20K miles.

I used the TR6 with bolt-on engine + 125 shot of nitrous. Reduced the gap to 0.040. With the current setup, when NOT running nitrous, an Autolite 104 at 0.050. That's roughly 1 step colder (maybe closer to 1/2 step colder) than the TR55. 104 was recommended by the engine builder.

You may have the only living Delteq…..

Steve40th396

Comp ratio 11 to 1, 3.73 gears with auto..
112+2 lsa 234 in and 242 ex 555 in, 562 exhaust.
Same plug different angle.
Iridium's are that good? Not much different if it makes car run better..