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Hello, I pulled my plugs and they look lean to me but I would like a different opinion. NGK plugs. Street car. 7040203 Quadrajet. I have a 383 with 10.5 compression, comp cam xr288hr, 1.6 ratio rockers, afr 195s, Edelbrock Q-jet performer manifold, rebuilt Q-jet done by CliffsHighPerformance, and a 4 speed. I have the timing at 26 initial, 10 mechanical, 36 total. If I let it sit there for 5 minutes the porcelain will have a tan color to it. However, the top of the porcelain is white after a drive and I thought that was the idle circuit. So I’m assuming I need to go down a size on my primary rod? Car doesn’t hesitate or anything, I had a vacuum leak that caused a part throttle hesitation but once that was fixed the hesitation went away.
From: At my Bar drinking and wrenching in Lafayette Colorado
It's not possible, and generally meaningless, to attempt to "read" a plug for mixture range if you are using current pump gas in the engine. Using modern blend pump gas, the plugs will appear clean and colorless across a very wide mixture range, making any interpretation based on color generally pointless. If the carb is running lean, you will have actual indications of the condition, such as stumbles & hesitations, surging, backfiring/popping up through the carb, poor throttle response (i.e., "lazy throttle") and poor power, if extreme. If none of those conditions exist, chances are you are not running lean. The only accurate way to tell is to use a wideband air/fuel meter on it. The Honda guys in the linked article above are talking about racing applications, and they're running race gas. "Reading" plugs can have some meaning if you're running race fuel (which has most of the "good" additives that were in the pump gas used in the 1960's), but it's still a very inaccurate way to determine carb setup and tuning.
Lars
What Lars says it of course very true. How the engine responds and acts, lack of pinging or blubbering ultimately dictate more than plug reading.
That being said more supporting info has never led me wrong. I’ve always read my plugs to either confirm or show a need for a slight change to what I had already set.
some of the info in that link refers to street driving color. Particularly the section about the porcelain tip you’re asking about.
I’ve been running 32* with my AFR 180 eliminator heads and 10.6 CR. It seems to like that. I tried from 38* to 32* and settled on 32*. The difference between 34* and 32* was almost imperceptible, I however settled on 32* on the basis that less negative work was better and it accelerated ever so slightly better at 32*.
From: At my Bar drinking and wrenching in Lafayette Colorado
My dyno testing supports the fact that those heads deliver best torque and power at 32 degrees total. They have very good combustion chambers, and power drops off quickly as soon as you give the engine more than 32 total. You got it nailed. A stock iron head needs 36 for best power.
Lars
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
IF the performance is there and its not giving you a lean backfire, then run it...IF yo are still worried or concerned take it to a shop and have them stick and AFR probe in her and see what she is running at. If you are into performance buy and AFR gauge and hard mount it in the car.
My dyno testing supports the fact that those heads deliver best torque and power at 32 degrees total. They have very good combustion chambers, and power drops off quickly as soon as you give the engine more than 32 total. You got it nailed. A stock iron head needs 36 for best power.
Lars
I’ll try 32 degrees and see how it likes it ! Thanks for the tip.
Lean Quadrajet
