1970 spark plug gapping

[D S.]

I gave up on the archives to find out this information. Mine is a stock 1970 454/390, if that matters. I have R45Ts to install. Is the gapping .035 or .040 or .045?

Thanks,
Scott Sims
Texas Chapter

[Michael D.]

Re: 1970 spark plug gapping

.035. If memory serves, it's printed on your tune up sticker.

[Pat M.]

Re: 1970 spark plug gapping

I think it's also in the service manual.

[Ken P.]

Re: 1970 spark plug gapping

Lots of information here:

http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html

[Joe L.]

Re: 1970 spark plug gapping

All-----


The only spark plug gap that anyone with a 1953-74 Corvette has to know is 0.035". ALL 1953-74 Corvettes specified this gap.

[Joe C.]

Re: 1970 spark plug gapping

The reason for larger gaps was because HEI enabled it beginning in 1975. As stated, anything prior to that used low voltage coils which would only allow gaps as large as .035".

[William F.]

Re: 1970 spark plug gapping

Looked up specs for AC "Rapid Fire" plugs on AC web site and they recommend a .040 gap for use in earlier(non taper thread) big blocks such as my '67 L36. I have non transistor ignition, standard coil, etc. Would .040 or .035 be best in this case?

[Michael W.]

Re: 1970 spark plug gapping

I'll bet you .005" that it will make no difference.

[Joe C.]

Re: 1970 spark plug gapping

I'll bet you .005" that it will make no difference.

Mike,

I've been meaning to ask you this for awhile. I heard that you knew the answer to this: Why did racers back in the day like to "short gap" their spark plugs?

[D S.]

Re: 1970 spark plug gapping

All-----


The only spark plug gap that anyone with a 1953-74 Corvette has to know is 0.035". ALL 1953-74 Corvettes specified this gap.

Thanks, Joe! Now that I have five new spark plugs installed tell me the tricks to 1.) get the plug boots to release from the old spark plugs. 2.) get to the three spark plugs on the passenger side behind the AC compressor and dipstick tube brace. I've got the car jacked up in hopes it will be easier from the bottom side. You small block owners are lucky.

[D S.]

Re: 1970 spark plug gapping

Lots of information here:

http://www.gmheritagecenter.com/gm-h...tion-kits.html

Ken, thanks for this! Saved it as a Favorite. I couldn't find a service tag and I have a 1968-1072 Corvette repair manual that I could not find the answer there.

[Michael W.]

Re: 1970 spark plug gapping

Mike,

I've been meaning to ask you this for awhile. I heard that you knew the answer to this: Why did racers back in the day like to "short gap" their spark plugs?

To get to the other side? Dunno, ask Clem, he's old.

[Thomas H.]

Re: 1970 spark plug gapping

I don't have AC on my LS5, but I would venture that cars, such as yours, with AC are easier to get at from the underside.

I have power breaks and cylinders 5 and 7 cause me to do some contortions to get at them.

Tom

[Joe C.]

Re: 1970 spark plug gapping

To get to the other side? Dunno, ask Clem, he's old.

I already know the answer. I'd like to know if you do as well. Apparently, according to your post #8, you don't believe that widening the gap will make any difference. I disagree. The question is designed to determine if you feel the same way about smaller gaps as well.

When it comes to ignition systems, you remind me of Mr. Williams. You're both stranded in the year 1972, although his arrested development applies to all aspects of engine technology. His dissertations on camshafts, especially, are not always supported by thorough analysis.

[William C.]

Re: 1970 spark plug gapping

Remember we are talking about 1970 technology, and a high compression engine, the ignition system can get a little marginal at high rpms. The stock class racers commonly closed down the gaps to ease the voltage requirement for high rpm operation. This was done in conjunction with other tips of the trade all aimed a maximizing the likleyhood that the mixture would get lit under a max performance situation. HEI and other modern ignition systems pretty much eliminated the problem, although not without other issues, so it's relavent to a question of "in the day"