BBC Spark plug gap Question

[shadowwalker_02]

A couple of days ago i was hanging out with some hotrodders and we ended up talking about my truck and his hotrod. His truck is a '48 chevy truck, frame off resto with a stock gm 350 crate motor. He has his plugs gapped at .048" and that thing runs like a bat outa hell. He asked me what my plugs where set at and i told him .035". He told me I need to re-gap them at .050" due to having a hei. I plan on gapping them at .040-.050 and see how my motor likes it. Has anyone else heard something like this or tried this? What are your thoughts?

Now I did look it up and I came across this article. http://www.superchevy.com/technical...ories_electronics/sucp_0606_hei_distributors/


Myth 1: Inductive ignitions, like HEI - High Energy Ignitions, aren't as good for high performance engines and racing motors as CD-capacitive discharge ignitions.
This myth is only true when compared to stock HEI systems. Today, we are making high-output modules and coils that saturate fast enough to fire constant at high rpm. ( This firing ability also allows wider spark plug gaps-in the vicinity of 0.050-0.055-inch. The benefit of wider plug gaps is a more complete burning of the fuel mixture.) <-- Is this true?

 

[80' 427]

The first year of HEIs recommended .060 gap but later years suggested .045 to prevent burning up caps/rotors etc. I always use .045 on a Hei (unless on lpg) and .035 on points. I seriously doubt you will see more that .5 hp difference either way. I have never seen any real gain with MSD or other ignition mods on a PROPERLY working ignition system.

 

[shadowwalker_02]

Do you normally set your BBC's at .045"? I don't really plan on running a msd box or anything like that. Like you said a lot of people I've talked to said it doesn't really make a difference.

 

[80' 427]

Mine were at .045 with gasoline but on my camaro they are at .035 because the NO2 likes to blow the flame of plugs out and on my k30 LPG can be hard to light so I use .035 because alot of the old impco books I have recommend it. I reality it would most likely be fine at .045 in both cases. I would worry more about ignition timing.

 

[76zimmer]

my BBC is set at .045, and my SBC in the Vette w/ CD ignition is set at .045 also.

 

[dyeager535]

GM used up to .080" on the HEI setups (Olds was one). Same ignition parts as the Chevy, and without checking, I *think* they kept that spec for the entire run, although I see some mention of .060".

Personally, anywhere near factory gap is "good enough" IMO, as someone else mentioned, in your everyday vehicle, a .010" gap difference isn't going to be noticeable. If you gap them at the factory specs, any "gap growth" as the plugs wear isn't going to affect how it runs.

 

[diesel4me]

True,in 1975 GM started using HEI ignition and some cars like the Oldsmobiles had spark plug gaps as wide as .080 ,but after one year,they reccomended going to smaller gap plugs gapped under .060,most were gapped at .045,after a rash of complaints about plugs becoming flooded and not starting a engine in winter weather conditions...once the engine flooded,it would not even fire until a set of 8 new plugs were installed--the straight sixes stayed with a .035 gap after 1976 ,despite having HEI.................................................................................................While its true a wider gap will give a smoother idle,more low end power and more effecient "burn" due to the wider gap allowing more air/fuel mixture to be exposed to the spark,high speed performance will suffer unless the coil is a very high voltage one,that can fire the plugs at the higher RPMs anbd compression loads,that is why capacitive discharge ignition was developed to overcome that problem.......in extreme conditions the spark would tend to jump over the porcelain insulator or elsewhere in the ignition system like the cap,rotor or plug wires,wherever the path of least resistance to ground is,rather than fire the spark plug....but in actual real world scenarios,gaps over .060 dont seem to improve the daily driving street use engines efficiency all that much really...on a race track with high dollar ignition systems that isn't always true though..