BBC spark plugs
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BBC spark plugs

  1. #1
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    Default BBC spark plugs

    What do these plugs say to you. 476 BBC, hydraulic roller, aluminum heads, duel plane, 830cfm Holley 6.5 pv's 84/84 jets. Thinking of going 86/86 or 84/88.
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    To be honest those pictures don't tell me too much about the plugs in that picture. It looks like it might be rich at idle and it looks like the ground strap is telling us it might be OK with more timing. (but I am not sure) I also like to use a racing plug as the silver coating gives a nice temp line. The WOT tuning will only show down inside the plug. You either need a good magnifier or cut the threaded area of the plug off to see the bottom of the porcelain. What kind of fuel are you running? How much timing?

    in a perfect world I would use an O2 sensor and a GPS to tune. I would use the O2 for idle and part throttle and the GPS for full throttle tuning. Some engines like a lot of fuel for max power and some don't, hence the reason I don't tune WOT with the O2. Once I know where it wants to be from playing with it, then I can always shoot for what ever magic number that specific combination wanted. Change anything and you are starting over.

    I dialed in an engine on the dyno and it made its best power reading a little more rich than most. Then I changed carbs and its best power was more lean than I would have imagine. Performance engines are spoiled little brats. They don't behave until you give them exactly what they want.

    Paul

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    Thank you for the response. I don't have too much experience with reading plugs, every other boat/engine I have had definitely looked darker after a few days of running. I'm at 37* total timing now so probably won't give it anymore.

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    Quote Originally Posted by nos1967 View Post
    Thank you for the response. I don't have too much experience with reading plugs, every other boat/engine I have had definitely looked darker after a few days of running. I'm at 37* total timing now so probably won't give it anymore.
    Do your'e self a favor and back the timing down to 30 or 32 degrees and run it. Reason being is an engine will feel fat at a retarded timing setting and lean at alot of advance. Lean at advance and rich at retard. this simple test will tell you to change jets or not. Your'e plugs look fairly new but I do see some color starting and that is with not knowing how much time on the shown plugs. More info makes it easier to get a better response, idle time, cruising or at W.O.T. Altitude plays a big factor also.

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    3 days at havasu, so probably 8-10 hours of actuall drive time, several wide open passes and maybe 30-40 minutes of idle?

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    Quote Originally Posted by nos1967 View Post
    3 days at havasu, so probably 8-10 hours of actuall drive time, several wide open passes and maybe 30-40 minutes of idle?
    With that being said I would say you are on the lean side. Also for an engine that size and an 830 cfm carb I would definetly fatten up a pinch. Check your'e power valves and run 86 primary and an 88 secondary and see if you get better color. I'm a fan of chocolate brown and I would also go out and make a hard pass and shut down and pull a few plugs. Idle time kills reading a plug, But if you idle in and the plugs look that lean I would say you are definetly lean. I still don't know what heat range you are running. M

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    Thank you this varifies what I was wanting to do. Don't have enough carburetor experience to trust my instincts yet but I wanted to go 84-88, I will go 86-88 like you said. Maybe 88-88 or 86-90 as I'm putting on much better flowing exhaust.

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