Hello all.
Well I have my 496 running very well, and decided to put in a new set of plugs before I start driving it regularly. I realized that I have no idea which plugs to ask for. It has Autolites in it (sorry I don't have the number, I'm at work) and I could just match them up, but I'm not certain that the plugs it has are the best for my application. What got me thinking was when a friend who manages a parts house visited this weekend, and pointed out that I have the 13/16" plugs. He said that to his knowledge no 13/16" plug was used in engines that come with HEI, so they would have a smaller gap. I'm no expert, so I asked why I couldn't just open up the gap, but he said that if I opened the smaller gap up very much, the ground electrode would no longer be paralel with the tip of the center electrode, which would make it only want to spark to the closest point on the electrode. This is beyond my level at this point, so I'm wondering if any of you have run into this and can shed some light on what would be a good plug choice? I have HEI with a Mallory coil and ignition. Any info would be greatly appreciated.

 

First place to look is the head manufacturer. Find out their recommendations then go from there ... up/down with heat range.

 

Old chevy cast iron heads.

 

Then use AC, R45 or R45S and gap them at .035 for your best performance with or without a HEI, ..

 

Great, thanks

 

First, recognize that your 'friend' is no expert. You can adjust plug gap AND keep the electrod 'parallel' if you need to {not that it is a really big issue to begin with}; plus, HEI ignition systems use larger plug gaps in order to make use of higher energy capabilities of that system. Making the gap smaller would just defeat the intent of the H.E.I. system. (high-energy ignition....) As mentioned above, just go to the plug manufacturer's website or call them to get a recommendation for which is the right plug for your engine and the way you configured it.

 

Thanks, and yes, neither of us are experts. We both knew that HEI needed a larger gap though, sorry if my post was confusing. I didn't think I indicated that we wanted a smaller gap, only that the plugs designed for pre-HEI systems would come with a smaller gap that would need to be opened up larger.

 

I had the same issue when trying to decied what plug to run. I use mortec.com/castnum.htm to find what year a certin head casting was used and than look up a vehical of that year that may have used those heads on NGK.com to see plug options. OEM gaps are also given along with plug suggestions.

Neal

 

An HEI system does not need a larger gap. (An ignition coil does not know or care what the gap is.) A stock HEI system merely has more energy in it than a points system. You can use that additional energy in a couple different ways. You can open the plug gap if you wish, using up some of that additional energy in the form of additional arcover voltage, or keep the same gap and have the arcover spark last longer. Your choice.
Given that you have a combination of aftermarket parts hooked up to your HEI, it's anybody's guess if you actually have more or less energy (and energy is the key word here) than a stock HEI. Unless you have the technical specs of the Mallory parts to compare with the Delco parts, you're just flipping a coin on which setup has more energy.

 

Good info here, thanks to all for the input.

 

Yep, your right stock HEI systems do use a wider gap all the way to 080 on some OEM systems. But for best "performance" .035 is the way to go. And by the many questions that are asked on this and other forum's, most of them are for and about increased performance. Therefore .035 is the best gap even with a HEI or other electronic systems in any make of engine. My engine of choice is Chryslers or Donovans and all my hot rods are .035 using Nitro or Gas...And my plugs come no charge directly from the Champion Spark Plug company

But run it wherever you want. It was just a performance tip not a exercise in selling auto parts to stock cars. ....

 

I do appreciate the tip and I had already planned to take your advice. I'm sorry for so many questions, but what is the difference between the R45 and the R45S?

 

I'm wondering if you need a "T" tapered-seat plug. No one has mentioned this.

 

The reason I suggested the R45 or R45S is that you mentioned the old plugs needed a 13/16 socket to remove them. The ''T'' is a tapered seat plug for later model V 8`s and uses a 5/8 socket. The suffix "S" is an extended tip plug that projects deeper into the cylinders and may under domed piston conditions may or could make contact with the pistons. The heat range remains the same with the number 45 that is a good all around plug for street use. The AC heat range is from the coldest at 41 to a 46 which is the hottest. The 45 is in the middle and good for clean usage instead of fouling during idle time.

 

Excellent and informative, thanks again.