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A Lesson Learned

 
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osmiumfoot
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Joined: 11 Jun 2002
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PostPosted: Fri Jan 10, 2003 7:08 pm    Post subject: A Lesson Learned Reply with quote

When I started building my first engine 4 years ago I put it together in the shop of a friend of mine who has some serious race experience. He showed up one day with 8 NGK plugs for my Dart Conquest aluminum heads and I installed them without even thinking twice. Since then, on every tune I have replaced them with the same kind. Two weeks ago I had my heads jet cleaned and the machinist called and mentioned that he had noticed that the last 6 threads in the plug hole were carboned. Right now some of you are starting to smirk, because you already know what slowly dawned on me: my buddy had given me a set of plugs for iron heads that are almost 4/10ths of an inch too short for aluminum heads. For four years I have been starting the fire up in the spark plug hole! The aluminum heads need a 3/4 inch reach plug, I guess because the aluminum deck has to be thicker. The lesson: check everything yourself then have someone check it again for you.
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86GN
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1990 Chevrolet Corvette

PostPosted: Sun Jan 12, 2003 10:29 pm    Post subject: Reply with quote

Do those heads use a gasket seat plug or a taper seat ? I'm looking for a NGK number for a gasket seat .750 reach plug.
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osmiumfoot
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PostPosted: Mon Jan 13, 2003 12:18 pm    Post subject: Reply with quote

86GN - Taper seat. I'm taking the old plugs to the track opening in April and run both sets. What's your guess on the difference in ETs?
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Tue Jan 14, 2003 10:57 am    Post subject: Reply with quote

I'll throw out a guess of 2 tenths.
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86GN
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1990 Chevrolet Corvette

PostPosted: Wed Jan 15, 2003 10:26 am    Post subject: Reply with quote

I'd guess that you'd probably pick up a 10th or 2. I'll be interested to hear what really happens when you make it to the track.

What are you running for plugs now ?
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osmiumfoot
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PostPosted: Fri Jan 17, 2003 12:21 pm    Post subject: Reply with quote

86GN - The plugs that were in there were NGK UR5 gapped at 50. What's a good replacement plug?
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86GN
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1990 Chevrolet Corvette

PostPosted: Sat Jan 18, 2003 6:02 pm    Post subject: Reply with quote

The NGK TR series plugs are a .710 reach plug with a v-groove in the ground strap, taper seat. The TR5 would be the same heat range you had in there. The TR6 is one step colder. I'm going to be trying these in the Buick. It's fouling Autolite's in 2 warm ups now.
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osmiumfoot
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PostPosted: Mon Mar 31, 2003 11:44 am    Post subject: Reply with quote

0.390 reach plug = 12.94 0.750 reach = 12.71 And the winna is........Smoke!! MPH w/short plug = 104 Long plug = 106 Very Happy
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GTAracer
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Location: Southeast, AL
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PostPosted: Mon Mar 31, 2003 4:33 pm    Post subject: Reply with quote

Nice improvement!

Do all aluminum heads need a longer plug...or was that just specific for your set of heads?

_________________
89 GTA 305/5-Speed/3.45
69 Camaro X55/4-Speed/3.31

In theory, there's no difference between theory and practice. In practice, there is.
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osmiumfoot
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PostPosted: Mon Mar 31, 2003 6:42 pm    Post subject: Reply with quote

Thanx! I don't know for sure, but I'm guessing most aluminum heads, unless they're helicoiled, need more thread engagement because of the softer thread material, and therefore require a 3/4" reach plug. I'm in the process of rounding up a set of AFRs, and I think I remember reading that they take a 3/4" plug also. My big block heads are iron and have the shorter plugs.
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Mon Mar 31, 2003 10:19 pm    Post subject: Reply with quote

osmiumfoot ... nice gain.... lucky guess on my part. I'll definitely have to remember that one. (If I can come up with the money for aluminum heads).
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