Shorter Reach Spark Plug
Thread Starter
Racer
Joined: Apr 2005
Posts: 494
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From: Virginia
Shorter Reach Spark Plug
Am currently running Accel 414S plugs in 73-350 with aluminum heads. The plug threads are actually 1/4" too long, they are 3/4". A comparable non-shorty plug would be Autolite AR2593 or AC Delco 41XL. How do I find plugs that are 1/4" shorter (1/2" long threads)? Don't think there is any advantage to the plugs being too long. 
Drifting
Joined: May 2005
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From: Somers CT
Too long really??? I'm kinda doing the same thing, I have AC R43 something or other which have a 3/4 reach and I have a header interference problem so I ordered that same plug you have. The end of the threads are just about even with the edge of the combustion chamber of both the original ZZ4 heads and the new Brodix heads. I think the only other length is .340 but could be wrong.
Thread Starter
Racer
Joined: Apr 2005
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From: Virginia
Le Mans Master
Joined: Oct 2005
Posts: 9,429
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From: Macon, GA
Why do you want to swap plugs?
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Pro
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From: wilmington nc
Heat range may be your problem , but i kinda doubt it. My guess idle transtition slots. Have you tried a steady 60mph cruise for about 10-15 miles shut the engine down, (do not) let it idle then check plug color.
Team Owner
Joined: Aug 1999
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From: Ontario
Not sure this is what you are looking for but I will put the info out in case it helps. My 1967 327/300 can use Delco heat ranges from AC 43 (cold) to AC 46 (hot). I generally use 45 but it is very difficult to find AC 45 these days. Most modern versions are R (resistor) and S (extended tip). I looked for an equivalent to AC 45 and with a little help from C2 friends came up with NGK B-4: non-resistor and standard tip. They work very well and just for your note, the reach is 1/2", non-tapered.
The heads are original GM.
The heads are original GM.
Last edited by Paul L; Jun 1, 2007 at 12:52 PM.
Le Mans Master
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From: Butler Pa
Not if the threaded portion of the plug also extends into the chamber. Carbon can build up on the exposed threads making removal difficult and possibly destroying the threads in the head. Also, the sharp edges of the exposed threads can get hot enough to glow red, causing pre-ignition.
Thread Starter
Racer
Joined: Apr 2005
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From: Virginia
Not if the threaded portion of the plug also extends into the chamber. Carbon can build up on the exposed threads making removal difficult and possibly destroying the threads in the head. Also, the sharp edges of the exposed threads can get hot enough to glow red, causing pre-ignition.
Le Mans Master
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From: Butler Pa
Drifting
Joined: May 2005
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From: Somers CT
Both my stock ZZ4 alum heads and new Brodix alum heads use 3/4 reach plugs. The threads do not extend into the combustion chamber and should not, as bashcraft said in previous post.
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Racer
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From: Virginia
Instructor
Joined: Dec 2004
Posts: 216
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From: Lapeer Michigan
It could be a quality problem with the sealing surface cut to low allowing the threads into the quench/combustion area.
Do you have a gasket on the plug ?
3/4" reach calls for a gasket, putting in a 1/2" reach will cause spark efficiently and build up carbon/foul plugs.
Ford in the 60's had the carbon build-up problem from the threads in the quench area and the threads would break off in the head calling for it's removal.
Do you have a gasket on the plug ?
3/4" reach calls for a gasket, putting in a 1/2" reach will cause spark efficiently and build up carbon/foul plugs.
Ford in the 60's had the carbon build-up problem from the threads in the quench area and the threads would break off in the head calling for it's removal.