Spark Plug Recommendation
 

I have 496 strokers with AFR aluminum heads should I use a stranded tip or a projected tip plug?

Brian,

For N/A applications start with;

NGK R5671 A-9
NGK R5671 A-8 Hotter
Autolite AR 3933
Autolite AR 3934 Hotter

Blower AFR Plug
Autolite AR 3935

Bob

Why hotter with a blower?

Definitely +1 on the Autolite AR 3933, the shorter electrode arm reduces the chance of detonation. I talked to an old time off shore racer and they used to saw the tips of their plugs to prevent detonation.

-8 is hotter than -9....that's all that means. A -8 is not a 'hot' plug.

NGK rates heat range from -1 (hottest) to -9 (coldest). Therefore, -8 is still a pretty cold plug. As another reference, many street engines use -5 or -6's.

BTW: - is read as ' dash'....not minus'

The Autolite AR 3933 is listed as a non-resistor type plug. Will this cause interference with the stereo in my boat? If so, is there a resistor plug that can be used in its place?

Bud - totally going by the top of my head here. Autolite 3923 ? Check to see if I'm right.

Edit in: Damn, I was close. Eveything is right, other than being a projected tip plug. Damn...close.

Bud,

Brain is utilizing the 305 CNC chamber head which carries a different baseline spec. Your base plug is the 3935.

Bob

Bob, so it is the same plug as listed for the blower plug? AR 3935? I assume that is also a racing, non-resistor plug. I know most street cars run a resistor plug to prevent radio interference. Is that an issue on boats, or is the fact that the engine is 8 feet away behind the location of most stereo equipment enough distance to prevent interference?

I also see a Champion plug listed on the AFR site.

Thanks!

I have been running non resistor racing plugs, with CD ignitions for quite a while now. No issues.

If I was running a blower with Autolite plugs, I'd run the 3933 or 3934. The lower the number in Autolite is colder. NGK, the higher the number, the colder. As in, a 3933 would be a colder plug than a 3934. A -9 would be a colder plug than a -8 in NGK. You can get a -10 heat range in a NGK racing plug.

Mercury used a MR41T plug in their supercharged 525SC, 600sc, 800sc. The Standard non supercharged plug was the MR43T. A comparable heat range plug to a MR41T, would be a -8 NGK or AR3934 autolite. A comparable plug to the MR43T, would be a AR3935, or NGK -6. Thats for heat range purposes only, as the MR43T and MR41T were .460 reach, tapered seat plug for the GM iron heads. The AR3933, AR3934, AR3935, NGK 5671 series, are .750 reach gasketed style non resistor, non projected tip. The AR133, AR134, AR135, NGK 5673 series are .460 reach, tapered seat, non resistor, non projected tip. I would not run a projected tip in a forced induction engine, or actually any marine engine in my opinion. :helmet:

i wish a mutuial friend would have followed the last part of your post.