[Don Boc]

I have a 72 with a 454. I put a GM HEI distributer in. I was gaping the plugs at .045. Does that sound right? I haven't put the car on the road yet so it is idling alot and I keep fouling and loading up the plugs. I also was wondering if anybody has any tips on recurving the mechanical advance. I have a 4 speed with a 3.31 to 1 rear, the motor is totaly stock except for headers. What RPM should full mechanical advance kick in? Thanks Don

 

[IgnitionMan]

Yup, .045 will do nicely. larger gaps with a STOCK HEI will overheat the coil and module.

 

[68Malibu Blown 406]

Try to get the mechanical to start at about 1000 - 1200 rpm, let it all be IN by 3000 rpm. Attempt to have the mechanical advance about 18° so that the initial can be set in the 16-18 range.

HTH

 

[Schurkey]

Actually, billions of Buicks, Cadillacs and Pontiacs used a .060 gap without problems, and Olds used .080 (!!) on the 403.

Remember that plug gap is NOT just a matter of bending the side electrode until you can push a cat through the gap. Plugs have a designed-in gap range. A plug designed for a .035 gap may go to .040, but probably won't work well at .045.

The designed gap of a plug is dependant on the length of the side electrode. I'll give an example using AC plugs: an R-46TS (Chevy) supports .045, an R-46TSX (Buick) supports .060, and an R-46SZ (Olds)supports .080.

68 Malibu is right, mechanical advance should be "all in" by 3000 RPM. I suggest a total of around 35*, feel free to experiment with as much as 40*, but with the fuel urinated out of the pumps now, I don't think that much advance is going to help you. Really good, aftermarket heads may be very happy with as little as 32*. I however recommend that on a relatively stock engine, you stay with whatever initial timing is recommended for your engine (probably around 4* to 8*) and get the rest from the mechanical advance. Reason: 16 to 18 degrees of initial timing is going to DRAMATICALLY increase your idle RPM, and you'll go nuts trying to back the idle speed screw out far enough to get the speed down. Especially important on auto trans cars.

That will screw up the throttle blade relationship between the idle and idle transfer circuits of the carb, and may lead to off-idle stumbles that no amount of carb tuning will fix.

Fouling plugs at idle means you have a hugely rich mixture. Check the idle mixture screws, and while you're in there, assure that there is no sign of fuel "dripping" off the booster venturis at idle. (high float, heavy float, or leaking needle and seat.)

 

[IgnitionMan]

If the news hasn't reached you, yet, GM modified the plug gap specs for all those .080 spec gap HEIs back down to .050, because the extra gap caused coil and module failure.

This was done in the late eighties. Factory direced modification/specification change bulletin.

Depending on which color wire the stock coil has to identify it, the gap is either .045 or .050, no larger, even though all the manuals and core support tags didn't get revised with the new spec stickers.

Just FYI.