JBR

I'm about to install new AC Delco plugs in my 75 L48 I'm putting in standared R44tx plugs. What should my gap be? :cheers:

zwede

I've found 0.045" to work well with HEI ignitions.

JBR

Thanks for the reply ZWEDE, I thought .045 was what I wanted but at the auto parts store, they just told me it must be .060. Of course I have 6 already in set @ .045 Now I'm wondering if I should remove them and change to .060. The ones I removed were the wrong plugs and were set at .075. Yet the car seemed to run good. :smash:

zwede

1975 was the first year for HEI and the spec was indeed 060. They had problems with such a big gap and the very next year they changed the spec to 045. I experimented with gaps from 035 up to 060. 035 took longer cranking before firing and the engine ran a little rough. 045 worked fine. Bigger than 045 tended to create radio static with no change in how the engine ran, so I stuck with 045.

lars

Run the .045" gap. The trend on high performance engines, even with strong ignition systems, is for smaller plug gaps to assure that the spark will jump the gap. At elevated rpm and higher cylinder pressures, the spark can be inhibited from bridging a larger gap, resulting in misfiring. I participated in a dyno run with Dougan's Engine Service where we ran a 502 putting out almost 800 horse. MSD ignition system and top-of-the-line parts, yet best consistent power was produced wth a .035" plug gap to assure consistent firing in the upper rpm range.

NHvette

Interesting ....

Maybe that's why my 75 L48 is such a dog ... :lolg: :lolg:

mental note - keep gaps at .045 NOT the spec'ed .060

JBR

Have them all in now, took it for a ride last night, now that every thing is plowed. (these cars have great traction in snow) It ran just fine at .045. Hey NHvette your 75 acts like a dog, because it was designed that way. same as mine. I have dual exhaust and I'm going to remove the cats to see if that gives it a little more punch. :cheers:

Jvette73

Yeah the theory was the larger gap would make the spark longer thus igniting mixture better and its true. The problem is it increases the resistance for the spark to ground on the ground electrode on the plug. So if yur coil is getting weaker or anything else is not just right, the larger gaps can cause misfires as the charge will always search for the path of least resistance to reach ground. So its a fine line between make performance and reliability. Bigger for better spark but not so big as to cause misfires.

Ever tried side gapping the plugs? Whats involved is trimming back the ground electrode approx 1/16". After doing this, if you view the plug from straight down you'll see that the center electricod is now exposed directly into the cylinder. Then set the gap to.035 between the closest corner of the ground electrode and center electrode. Its an old school trick thats been around for a long time. The plug companies wont tell you about this because they want you to buy thier fancy new designs for more money, which do basically the same thing, expose the center electrode into the mixture more.

Last Place

:cool: :thumbs:

flood

You know if they just used two spark plugs everything would work better.


I use my gap at .060 and things seem fine. I guess I will pull them out here in a few and see what they look like. Maybe I will change to a less gap if there are problems. :cheers: