Spark Plug Reach

[Ball Racing]

Okay standard plug is the 3/8" reach,
but that leaves lots of threads exposed in the chamber which can lead to detonation, shrouded spark, less compression and possible flow disturbance.I also think you may need to run more advance on your timing with the short plug.

I took a old head placed the champion J8c plug in, then put a autolite 437, then a ngk B6HS.
The autolite was a just a hair longer threaded area then stock, and the B6HS was near perfect flush with the chamber in the head.(maybe 10 thousandths beyond flush)

I Can't believe the factory would put such a short plug in there.
Anyone played with reach length of the threads besides the heat ranges- tip shapes?

I put the longer plugs in the boat and made a test pass, but did not back up the pass with the short plugs so I can not say if it made more power.
(It was humid today with a lower barometer than when I last ran the boat.)

[Dave Neptune]

How about heat?

Daniel, what is the reach on the NGK? I don't really think there is much to be gained at the low RPM's we run these at, however every lil' bit helps. Part of the "short" plug could of been to keep it a bit cleaner when using the old fuels way back then. Also there was a tendency then to run rich for cooling considerations on load duty engines such as these.
I don't recall how thick my head is at the plug however I'll take a look. I like running the #8 as the heat range seems about spoy on and I would like to try the reach but want to stay with a cooler plug than I see most going to on this forum. I have no fouling issues and my engine is very tired.

Dave Neptune

[Sony2000]

I'm with you, and find these plugs to be too short, preferring to have the spark more in the center of the gas/air mix. With my old head, one cylinder had a little blowby around the plug and a Mercruiser 4 cylinder plug gave me the reach so i could add a soft washer over the chipped metal. Without the washer it used all the thread. It looked like a perfect fit.

[Ball Racing]

The ngk b6s is a 3/8" and the b6hs is a 1/2"

[Ball Racing]

Okay, a little testing with the longer reach plug.
SHORT PLUGS:
I have been fishing alot lately, leaving the engine idling for hours as I was scared to cut it off as I don't have a sail for back up
Anyway you could hear the motor loading up, and starting to stumble at idle, and I would keep uping the idle to try to keep it clean running.
And when I would move and throttle up there was alot of smoke to clear out (I use LOTS of MMO)
When I got back to the dock the plugs were pretty dark.
LONG PLUGS:
I repeated a identical trip with the longer reach plugs that were of the same brand and heat range, just longer.
The motor ran just as smooth as all get out, never had to rev it up to clear it out or keep it going after all that idling.
I ran it back to the dock like always and plugs were way cleaner than the shorts.

[Mo]

Here's what I have in mine...been in there a year now and about 90 hours...not a hint of problem and they stay nice tan / brownish color.

http://www.jegs.com/i/NGK+Spark+Plugs/739/XR4/10002/-1

[Ball Racing]

I tried those too.
I might see if they have those a step cooler and in 1/2" reach.

[sastanley]

I think i am running the NGK BR6S, since Maurice has had such good success with them.

I do have an RJ12YC in the #4 cylinder since it seems a little weak. Dave Neptune told me it was OK

Honestly, I've probably put as many hours on the motor in the last 3 weeks than I did all last season, so I need to pull them and take a look.

I'll report back next week...going to Southern Bay Race Week in Hampton in the AM..