Spark Plug Selection

[Bruce]

Once you get to (or through) the Reading Spark Plug thread, the next item is "what really is the right heat range?".

The short answer is, the coldest plug that you don't foul. Don't lean the motor down to run a colder plug, unless you definitely find HP. There's a fine line with, EGTs, AFRs, and plug readings when you really start going for max HP. There's a fine line with, EGTs, AFRs, and plug readings when you really start going for max HP. There's a fine line with, EGTs, AFRs, and plug readings when you really start going for max HP. The reason the gurus are such gurus, is that they've paid the dues, in learning exactly what is what. Yunick, Roush, Yates, have all paid some serious money to learn the lessions of the above. Armed with alllll the best book learning in the world, squeezing every last HP out an engine, still has a huge learning curve.

With that said:
I talked with *Larry* the Autolite rep, at 1-800-890-2075, today, and come up with the following data.

A 23 is the coldest plug, of that series for normal passenger car use.
To go any colder means going to a racing plug.

A 23, is equivalent to a AR13, and one range colder then that is a AR12 (both are still resistor type plugs).

From there one can go to a *standard* racing plug (non resistor).
With a AR 134, being the same range as the AR12, then a AR133, which is one range colder, and then a AR132 which is the coldest plug of that series.

Hopefully, I'll be adding to this once I get my plug order in, and talk to the NGK, and AC techs..

[Bruce]

.
8/2/5
BTW, when in doubt start with a plug that should be **COLD** enough. Starting with too cold of plug, means a fouled plug, starting with too hot of plug, which can cause pre-ignition which a knock sensor isn't even tuned to hear. So for the less then pro tuner, can start off with doing alot of damage, though a relatively simple error.


BTWII, it's easier, and cheaper to be a little too rich, and a few degrees short of what the accepted standard is, that'll just cost you a few HP, too lean and too much advance can be expensive.

[Bruce]

8/3/5

After running the UR5s for a while they look to be about the same heat range as the Autolite 23s. No signs of the plug overheating, nor traces of soot.

I have run a set of the NGK BPR6FS, and while they lean more to the bone white side then the 23s, or 5s, they're not signifigantly colder then either of them. This was a short term plug reading, just to get an approx., of what things are looking like.

I now have a set of the AR134s, and AR12s (AR=Autolite Racing).

So there's still more to come....

[GNVYUS 1]

Bruce how come no mention of the AC44's, 43's and 42's?

[Bruce]

Bruce how come no mention of the AC44's, 43's and 42's?

Those are the stock plugs +- a heat range, and well, have been pretty well covered in the various boards. The readings are the same so in that reguard they've been covered. Not to mention that I only have so much time, and money to put into projects like this.

[Bruce]

Not knowing how cold an AR-12 was, I installed just one, to see if it was even close, or if it just fouled out. Well, after a number of cold starts and driving around, it looks bone white. So today, I installed a second one in a cylinder that's using a trace amount of oil to see how it does. If that passes muster, then I'm going to try the AR-134s.

[Bruce]

Installed a AR-134 today...
Driving around town, and mostly cruising it showed signs of being just a tad too cold. If I was going do any racing, it might be about right.

The AR-12s I have in now look pretty close. I'm going to try a couple more degrees in cruise/ idle and see if that helps get rid of the *soot*. I hasten to even call it that, since it's so light.

Even if they work out to be a tad too cold then I have the NGK BPR6FS as a fall back plug. The UR5s, and the Autolite 23s, were both too hot of plug/ had a projected nose, that I really didn't need.

Again, this is just stuff that's worked out for me, and you're results may (will?) vary.

[Bruce]

Welllllll,
after a week of burn outs, cold starts, and a huge case of the crazies I can say the NGK BPR6FS, are for me.

And, I learned something new.
Some time ago, a few racers had been explaining to me how they were tuning to get a gray reading the plug, and the *gray* was from being *just* borderline on detonation, and the gray was supposedly due to the high IR/UV from having so many free radical ions....

Well, take the perfect light tan/ beige plug, and going down a 1/2 or maybe one full range of colder plug can also do it.

[weeee_6]

Those are the stock plugs +- a heat range, and well, have been pretty well covered in the various boards. The readings are the same so in that reguard they've been covered. Not to mention that I only have so much time, and money to put into projects like this.

Bruce,

I understand... but where do they rate heat range wise, educated guess would suffice, the the NGK's you settled on (for now).

thanks Bob

[Bruce]

Bruce,
I understand... but where do they rate heat range wise, educated guess would suffice, the the NGK's you settled on (for now).
thanks Bob

Let's see if I can get all these numbers right.

The AC42 are a range colder then the stock 43s, and the 42 look about like the Autolite 23s. The UR5s are a tad warmer then the 42/23s, but seem to be a touch colder then the 43s. Then of the plugs that did work the BPR6FS, were the coldest. I'm not going to prefess that the manufacturers or others, results will match what I saw, in this one application. If I was to start work on a *new* car, I'd probably grab a set of the A/C 42s, Autolite 23, or the BPR, to start out with.

Helps?.

[Bruce]

R.MERRITT, found this link
http://www.in.net/~eholman/ngkplugs.html

Reaper, found this one (eye sight warning)
http://www.clubplug.net/index.html?....net/cross.html