What would cause the set gap of .040 to open up to .060 in 68 runs? This is a 496 bbc bracket motor with 13 to 1 comp. on c-12, timing set at 37t, autolite AR 134 plugs. Thoughts?

One plug or all 8?

quote:

Originally posted by imakehp:
One plug or all 8?

The reason I ask is there's only 2 things I can think of that would OPEN the gap

One is maybe detonation......maybe

The other is the plugs were gapped @ .060" to begin with...

Not trying to sound like a smart ass but the gap opening is probably 99% harder/less likely then closing up...

I'd re-gap the plugs and keep an eye on them..

a close inspection of the strap and electrode should answer your question

I set the gap on my NGK plugs at .022

I am amazed you got those Autolite AR134's to last 68 runs. Same plugs were good for no more than 40 every time I used them, sometimes a lot less.
Toss 'em in the barrel and get some NGK's, same price, they last forever, and they won't send you looking for phantom ignition or fuel problems that don't exist...
Direct replacement is NGK Racing plug # R5673-8, (Lot of parts stores carry them, but not under the actual plug # - NGK Part Number 3249 will get you a box of 4 at your local O'Reilly store, etc).

Thanks for the replies fellas. Have been thinking about those NGK plugs for a while, my engine builder said the same thing as you Jim. The ground strap looked as if it was pulled open with pliers, yes all 8. I'm going to give the NGKs a shot but .022 seems kinda tight for MSD. I never heard that much negativity towards the auto lites. Thanks again.

I'm using the same plug as Jim and my engine builder said " pull them out of the box and bolt them in" .... LOL I still check them and they seem to come out of the box right at .030 , I'm using a MSD for fire... he is one funny guy but his stuff runs fast and consistent so I never question him .....

Like J178RED says, they all seem to come out of the box right at .030 gap, which works great for me.
I forgot to note, the R5673-8 P/N 3249 is a non-projected tip. If you want to run projected core nose plugs, the series is R5674. The -8 is P/N 5657. ( -8 heat range is a great all-around choice. Heat range goes up as the dash # goes down, so if you run alky and want a bit more heat, go to a -7, or for a colder plug, -9).

This message has been edited. Last edited by: FootbrakeJim,

Jim did you get that correct on NGK beat range? I am under the impression that smaller # is hotter. I keep the gap at .25/.30 no point in taxing the ignition any more than necessary.

Smaller is hotter on an NGK. -7 is hotter than -8 and so on.

Thanks, that's what I thought. I may have misread Jims post.