1964 327-365hp Spark Plugs

[Larry M.]

I have a box of AC 45S spark plugs, will they work okay in my 64 327-365hp coupe? Thanks for any info........

[John D.]

Re: 1964 327-365hp Spark Plugs

Larry, S means extended tip. They might hit the pistons. I did read here one time that if you index the plugs the extended tip may be OK. I think it was Clem that said that but am not sure. John

[Duke W.]

Re: 1964 327-365hp Spark Plugs

Unless the heads/block have been sigificantly milled, it's unlikely that the 45S will interfere with the pistons. Many, including me have used extended tip plugs in SHP/FI engines. They are the correct AC heat range (5) for normal road driving and should work fine.

Duke

[Gene M.]

Re: 1964 327-365hp Spark Plugs

Is there much advantage to having the plug (45S) extend deeper in the 461/462 heads?

[Duke W.]

Re: 1964 327-365hp Spark Plugs

For a given heat range, extended tip plugs tend to have a wider foul-free operating temperature range.

They move the spark slightly - maybe about 1/8" - closer to the geometric center of the combustion chamber, which should reduce combustion time and best torque spark advance, which will increase thermal efficiency yielding greater torque/power, but it's probably too small to measure compared to normal variation in back to back dyno runs.

I discussed this in my San Diego presentation and illustrated the effect by comparing the best torque/power spark advance of the modern LS7 and a modern pentroof four-valve chamber to a vintage small block.

In GM's new LT1 presentation they mentioned the large amount of computer simulation time used to optimize combustion chamber geometry, injector location/spray pattern, and spark plug location, and it resulted in a very uniquely shaped piston crown.

All this engineering will improve C7 fuel economy in addition to the substantially increased low end torque of the LT1 compared to the current LS3.

Duke

[William C.]

Re: 1964 327-365hp Spark Plugs

From experience---You will close the gaps on the plugs (at least a couple of them) IF you don't index them with the open side of the gap toward the piston, and IF you try to run the engine to 7000 rpm. In my youth, I was guilty on both counts, Circa 1968-69

[Clem Z.]

Re: 1964 327-365hp Spark Plugs

From experience---You will close the gaps on the plugs (at least a couple of them) IF you don't index them with the open side of the gap toward the piston, and IF you try to run the engine to 7000 rpm. In my youth, I was guilty on both counts, Circa 1968-69

just mark the ground electrode fixed location on the porcelain with a magic marker and when you install the plug as long as you can see the mark from the top you will be OK. DO NOT use a lead pencil. back in the day i also had the problem of finding a miss after installing the extended tip plugs caused by the gap closed by the piston