View Full Version : spark plug gap question

cadillac kevin
04-10-13, 10:15 PM
I pulled the spark plugs on my caddy (1986/ 87 spec L05) and replaced them with some .060 ac delco ones I had bought a couple years ago for the 307 (since I knew that some years of the 350 chevy used .060 plugs).
The plugs I pulled out of the motor (which were all in pretty good shape and I kept in case the ones I put in were incorrect for the engine) were autolites gapped anywhere between .035 and .045 (seems like someone put them in without gapping them first) and the engine ran pretty good on them (they might have been a couple years old at most).
I decided to do some reading online about the gap just to make sure that .060 was ok and the first several links I tried had idiots flaming each other about spark plug gap and how (pick .035, .045, or .060) was horrible for the engine and would kill power and/or hurt the HEI blah blah blah. So I figured I'd ask the guys here.
Will running .060 gap plugs hurt my 350?
What gap should I be running?

04-10-13, 10:34 PM
HEI powered ignitions were spec'd up to .060, and they are all essentially the same - lower specs are tailored to the specific engine and not influenced by HEI's capabilities. Either way, I'm not sure why there'd be reason to question the spec for our specific car. Gap them to spec and be done wit it. The system is made to sustain the wider gaps, which is the whole point of it's implementation. .035 gaps were suitable for points/condenser ignition, which couldn't sustain anything hotter, but were pretty much abandoned when HEI was introduced... To sum up, factory HEI can handle .060 and smaller with no risk to the ignition system itself, but the gap still needs to be correct for your engine's CR and combustion design.

04-10-13, 10:35 PM
My Shop book says .035 for the L06 350. for the model years 91/92

04-11-13, 01:31 AM
the correct gap is .060 for HEI as eluded to previously.

04-11-13, 09:07 AM
My Shop book says .035 for the L06 350. for the model years 91/92

This has come up before and I thought it was a misprint. It makes no sense to run such a small gap nowadays but apparently that is the case, or it is really a misprint. Most Chevy v8's recommend .045 and Oldsmobiles recommend .060. The old 403's used to run .080 gap for some emissions reasons but hotrodders would run .060.