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Author Topic:   Spark Plug and Gaps
Dirt Roller

Total posts: 21
posted May 20, 2005 07:43 PM  
Did a search on this site, came up with alot of varying opinions, mostly from years ago. MY QUESTION: Motor is a Dart Block 414 CID, 12.5 to 1, Vortec Heads(tricked out) big cam, best of everything, running 110 octane racing fuel. I have been running an AC Delco R42T plug with a new D.U.I. Ignition, gapped at .45 due to the fact that DUI says you can run gaps up to .55.
I was told by a very respected car and engine builder (at the racing school I just attended), who said I definitely needed to lower the gap, and switch to a racing plug. So I bought some Racing NGK stock #3442, part #R5673-9 plugs, but did not trust the bonehead at O'reillys autoparts and did a cross reference of the r42t to the NGK. I do not think he gave me the right plug, numbers are totally different. QUESTION 1- what is the best racing plug at a reasonable price. QUESTION 2. what is the best heat range for my application. QUESTION 3- What is the best gap for my application.
Thanks to all, I appreciate the responses greatly.

Dirt Forum Champ
Total posts: 516
posted May 21, 2005 05:53 AM  
Champion RS12YC
Autolite 103 racing AR764
Ac Delco R44 LTS

All 14mm .708 reach

Hope this helps, I run the autolite 103 in my vortecs.

Dirt Freak

Total posts: 493
posted May 21, 2005 07:33 AM  
I always ran those same NGK plugs on gas with .030 gap with great results, seemed worse with larger gap. I used -7 heat range though. That was with Dart Iron Eagle and/or world sportsmans heads.

The Joy of Six website

Dirt Freak

Total posts: 402
posted May 23, 2005 10:22 AM  
Bigger gaps mean better flame front propagation till the ignition system can't keep up with the discharging of the coil.

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