Pull plugs today.............

[badmix]

Redoing my headers, so figured it would be much easier to replace my spark plugs while headers are out of there, and boy was I right, took no time at all.

I checked the gap on the old plugs, they were around .060 , factory is .045. I know I gapped them before i put them in years ago. Kinda surprised the gap was so big and it was the same on all 8 plugs.

so, lets play a game from the engine ppl on here.

What are the Pro/Cons of going from .060 to .045 (factory)?

 

[kennyw]

Stock HEI ignition?

 

[badmix]

Pretty much, its not OEM, its a Mallory Dist with related coil and MSD wires. No ignition boxes, etc.

 

[diesel4me]

From what I have read,wider plug gaps can improve idle and combustion,(provided the coil has enough zap to jump the gap under compression),and smaller gaps will decrease the chances of misfire under a load,or at high speed,but may also make the engine idle a bit rougher..

GM had some engines with HEI using plugs with .080 gaps in 1975,they found they were having cold start and fouling issues on some vehicles,so in 1976 they reduced the gap to .060 or .045...Chevy's usually had either .035 or .045 gaps ,Olds & Buick were the ones that experimented with the super wide gap plugs..

 

[4xcrazy]

I had a '78 Cadillac Fleetwood Brougham (land yacht) that ran .060 gap.

I was actually considering widening the gap a tad on the Burb to see if it would assist in an annoying idle condition.

 

[Stomis]

I thought stock gap was .035, at least for a TBI motor. I know its commonly recommended to open them up to .045. Within reason the more open the gap is the better for the engine, but the ignition system needs to support this otherwise it can have a reverse effect. If .060 was working I suggest keeping it.

 

[badmix]

Well, ill leave the plugs at .045, and see how it runs. I know how it runs with the .060. lol. ill update this thread.

 

[Blue85]

To do a fair comparison, you would need to run both gaps on new(ish) plugs. Even the "wrong" gap might do better on a new plug, compared to the "right" one on 40,000 mile plugs.

 

[dyeager535]

I've run gaps all over the place, and besides different engines/years, as mentioned, so did GM.

Never noticed difference in economy (about the only way any of us can see if there is efficiency being gained or lost) so I figured it wasn't doing anything. I'm OCD when it comes to MPG monitoring BTW, not just a random observation that I didn't check 10+ times lol. I've also heard that initial big gap was a problem for longevity, but I'm not so sure I buy that reason...Olds (for one) ran .060" with the same ignition setup until 1990, if gap reduced life of the ignition components, that would be seen with the Olds as well, and I've not seen/heard any issues. I suspect it had more to do with emissions/engine design.

Benefit of gapping small (.035) is that as plug gap grows from wear, you've got more time before the gap gets really big.

On my new car (OBD2) when plug gap grew enough it triggered a CEL for cylinder misfire, but that's 10:1 on 87 octane, so it's very picky about that stuff. Relatively low compression truck engines don't care nearly so much.

And no, I don't just replace plugs. If I can re-set the gap, and they aren't physically damaged other than some normal erosion (or more recently, carbon marks from compression leakage where the insulator is crimped to the body), I re-use them.

 

[badmix]

Thanks everyone.

I grew up re-using plugs, just take em out, wire wheel them, clean them off with carb cleaner and put em back.

 

[diesel4me]

Here,on my trucks,especially ones used for plowing,if you dont replace the plugs in 2-3 years,you'll need a bolt out extractor to get them out--IF they'll come out!..
I have had a few rot away at the hex in a few years and blow the porcelain right out before!....nothing like that noise to make your sphincter grip the seat cover!..