Inliners International Forums General Discussion Engines Plug gap?

I've been bored lately so I have been doing some fine tuning on my 250. I've got the Ignitor 1 Pertronix kit installed right now. I run the motor on 87 octane and it's a daily driver. I had the plugs set at .035" (points spec) so I opened them up a little last night to .042". The engine seems to run a little smoother, the plugs are nice and tan(all 6). I was wondering what some of you other guys are gapping your plugs at with HEI or Pertronix kits. I looked in my Haynes manual for '67-87 Chevy trucks and found something interesting.

If I remember right 1975 was the first year for HEI, right? For 1974 Haynes' lists 250,292,350,454 at .035" gap. 250 uses plug AC-R46T, the rest use AC-R44T. In '75 they list 250,292,350,400,454 at .060". 250 uses AC-R46TX, the rest use AC-R44TX. In '76 they list the 250 and 292 at .035" and the 350,400,454 at .045". The 250 uses AC-R46TS, 292 uses AC-R44T, 350-454 uses AC-R45TS.

I know this is alot of info, but what gives? If HEI started in '75 and they increased the gap why in '76 would they go back to .035"? I just find this odd. Doesn't a hotter spark allow you to increase plug gap, which will provide better combustion of the air/fuel mixture and decreased emissions? I'm just trying to get an idea of what will be about right for my truck. Thanks guys. John.

I am running AC-44's @.060 gap with the IgnitorII in my 1975 292. Engine starts on the first spark, never misses, and really hauls when you slam your right foot through the floorboards!

There are no rules for setting gaps or type of plugs to use. There are standards to start from but what ever works for your motor, where you live, driving habits, etc. then you find out by testing. everyone has a favorite but what works in your situation usually is best!


PS- If your just bored, I've some things you can do! Don't mess with what works.
RapRap
1940 Chevy Coupe

[This message has been edited by raprap (edited 07-01-2003).]

The first couple years, they used .060. After that they changed to .045. Why? Who knows? In the early HEI days the rotor had a bad habit of burning a hole in it and shorting to ground. When they switched to the white rotor instead of the black, that cured the problem. I think they closed up the gap because of too much resistance, making the fire burn thru the rotor.Most Oldsmobiles used .080, so either will work. Joe

raprap--Just drop me an email on what you want me to do j/k I'm actually going to be getting a fuel cell and some other parts in about a week, so I shouldn't be bored much longer. I think I'm going to open them up a little more .045"-.048" or so, and see how she does.

Joe Dial--Thanks for the info. I just thought it was pretty odd to see the specs change like that.

Thanks guys for the help. I can't wait to get my fuel cell. Better traction, no more gas fumes, and more leg room. Thanks. John.