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Author Topic: spark plugs  (Read 318 times)
BCOWANWHEELS
6 Banger
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Location: KINGSPORT, TN.

« on: March 15, 2018, 09:13:07 pm »

building a carbed 306, hi compression, tunnel ram, 2 x 660 holleys, maxd out gt40pn heads. electronic ign. what spark plugs will work best...............help,,,,,,,,,,,,,,,,,,,
thanks bob
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I BELIEVE IN JOHN 3:16
David Claflin
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Location: Redneck Riviera (Ft Walton Beach Florida)

« Reply #1 on: March 16, 2018, 01:15:11 am »

GT40 Heads:
AUTOLITE
stock--765 (Heat Range - 5) [14mm, .708 Reach, 5/8" Hex]
1 step colder--764 (4) or 104 (4) [14mm, .708 Reach, 5/8" Hex]**
2 step colder--103 (3) [14mm, .708 Reach, 5/8" Hex]**
-----AR473 (3) [*recessed tip, racing plug]
-----AR472 (2) [*recessed tip, racing plug]
**The difference between the 764 plug and the 104/103 plug is the thread. The 764 plug is a half thread whereas the 104/103 plug is a full thread. The full thread plugs are duplicates of the half thread plugs in every other aspect, they both protrude the same amount into the combustion chamber.

NGK
stock--(TR4) 3754 (Heat Range - 4) [14mm, .708 Reach, 5/8" Hex]
1 step colder--(TR55) 3951 (5) [14mm, .708 Reach, 5/8" Hex]
2 step colder--(TR6) 4177 (6) [14mm, .708 Reach, 5/8" Hex]
-----(B8EFS) 1049 (Cool [*recessed tip, racing plug]
-----(B9EFS) 1085 (9) [*recessed tip, racing plug]
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1990 Red LX, 306, 80MM, ported gt40's, ported explorer upper accufab longtubes, 3" exhaust, 4.30's, 336/331
1985 LTD LX 347, 205 11R's, TFS-R, 90MMTB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
juiced coupe
Six figures worth of don't give a f*ck
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Big Block
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Location: Pascagoula, MS
The land mass between New Orleans and Mobile


« Reply #2 on: March 16, 2018, 11:55:46 am »

With those ancient TRW domes and P heads, you will be ~11:1 compression. Maybe a little more, depending on if or how much the block and heads have been cut.

Check your clearances with those pistons. They have been known to hit the plugs on many heads with more modern chambers, requiring a notch be cut in them.

I'd probably start with the TR6 or 103 plug.

If you are wanting to use pump gas, you may be facing other issue. While 11:1 compression is commonly used with pump gas, doing it with a an ancient dome piston and cast iron heads will be a little more tricky. Whatever cam you choose will likely be the determining factor.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
BCOWANWHEELS
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Location: KINGSPORT, TN.

« Reply #3 on: March 16, 2018, 05:05:06 pm »

I,LL CLAY THE CHAMBERS FOR SURE BUT WITH 54CC 289 HEADS AND 540 LIFT CAM NEVER HAD ANY PROBLEMS. COMPRESSION WAS 12-1 PLUS. GONNA RUN MOSTLY AVE GAS-RACE GAS 110 MIX. ENGINE IS FOR MY T-BUCKET. HEADS FOR THIS ENGINE ARE GT40P
THANKS
BOB
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I BELIEVE IN JOHN 3:16
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