Spark plug selection 408

Paul P · Posted: Sun Apr 17, 2011 12:14 pm Post subject: Spark plug selection 408

I'm going to order some NGK's today. I need the gasket 3/4 reach plugs with the Dart 17's. The catalog is here. http://www.ngksparkplugs.com/docs/RacingSpecs2010.pdf

The plugs I used to run were R5673-7's with the old combination 11.75 compression.

New combo 13.2 compression I am leaning towards the R5671-A9's. These should run well with the occasional N20 hit. Any suggestions?

af2 · Posted: Sun Apr 17, 2011 6:02 pm Post subject:

Paul, I found the 9's to be too cold on mine. Went back to 8's and no problem. The 9's were trying to foul on the return and to the line.

10sec.et · Posted: Sun Apr 17, 2011 10:57 pm Post subject:

i agree with 8's. i would probably start with 7's but i like to read the plugs and tune from what i see.

Paul P · Posted: Mon Apr 18, 2011 12:06 am Post subject:

ok thanks I was leaning to the 8's but the only advise I had was from a tech at Jeg's.

Paul P · Posted: Tue Apr 19, 2011 3:53 pm Post subject:

Ordered a set of 8's and 7's from Rock auto around $30 delivered.

dawg · Posted: Sun May 22, 2011 3:15 pm Post subject:

I use autolite AR3934 with nitrous, great success.
Ill use AR3935 for regular street driving
perfect heat range on my 406

William Jones · Posted: Mon May 23, 2011 2:38 pm Post subject:

I use 8's in mine its 15.3 to 1, but I perfer to use C59CX champions.

Bam

Paul P · Posted: Mon May 23, 2011 9:33 pm Post subject:

Champions? Sorry never had good luck with them. I only use them in lawnmowers and weed wackers. Laughing

NGK 8's and 7's should do the trick.

The Autolites are tempting. I used to run 25 and 26's back in the late 80's early 90's.

William Jones · Posted: Tue May 24, 2011 12:08 pm Post subject:

Yeah I used to say the say thing until I did back to back testing the Champion race plug CX series has a cut back electrode and was faster than the NGK's. But I have to change the champions about every 60 passes. The NGK'S are a great plug and are more commonly used with power adders than the Champions. The Champions get used alot in all motor combinations. But to be honest either way your car is going to haul ass.

Bam

Knarley Darley · Member Joined: 22 Apr 2004 Posts: 1149 536969.38 points

I would say the 8s also. I have run the 9s with 17 to 1 and had success with them, but the jetting and especially the pump shot off the line are critical for the engine to run clean without missing. I usually run the 8s. If you run NA the 7s, should be ok. Just curious what fuel do you like? On another note the NGKs are the easiest to tune with. I look at the threads of a new plug after 1 run and they should be discolored (heated) about three threads in from the combustion chamber. Four threads of discoloration and you are to lean, and Two is to rich. I find it impossible to get a good read on any other brand because they all have a black coating on them. Every time I make a change, I screw in One or Two new plugs for a fresh read.

Paul P · Posted: Mon May 30, 2011 9:52 am Post subject:

I like VP C-12 been running it for years after Power Mist had some issues with quality.
I'll be running a wide band O2 to tune the mixture but the heat range will be easy to see too. Usually the annealing ring on the center electrode is visible. NGK's are good like that too.