Found this on the Chevelle site about a year ago. Interesting read. You don't have to believe him, but to me, most of it at least makes sense to me.
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There have been some here on the boards that simply refuse to accept FACTS on tat has evolved in HEI spark plug gaps, tech, other facets. There seems to be a small handful that simply don't get how it works, nor the changes GM made along the way to reduce problems created by wrong spark plug gaps.
FACT, The GM HEI was NOT developed as a performance ignition system, it was designed strictly to be able to properly fire off increasingly leaner fuel/iar mixtures in EMISSIONS engines. This required a few parameters to be adhered to.
The first criteria was to build an ignition system that would not degrade, nor change timing specifications over a minimum 50K miles, to insure emissions were not increased.
The second was to make a spark great enough to bridge a slightly larger spark plug gap than a point system made, so, as fuel molecules were reduced for leaner mixtures for emissons, there would be enough gap in the plug to "catch a fuelk molecule" to light off the burn in the combustion chamber.. This took creating "drivrs" in the HEI module to increase dwell charge time to the coil, store more energy, to make the larger gap function correctly over a point system.
Along the development of the HEI, some engineers decided that to fire off ever more leaner fuel molecules, the HEI needed increased spark plug gaps. So, Pontiac, Buick, Cadillac, and especially Oldsmobile simply opened up their pluggaps first to .065, then, to .080, with NO changes to any of the distributor components to accompany the increased gaps.
What this did was create, at the tme, largest warrantee failure replacement program GM had, from HEI modules and coils failing very quickly on newly sold vehicles. The first 3 had about a 40 percent failure rate, Olds had over 70 percent failures when the spark plug gaps were increased to fire off ever leaner fuel mixtures.
This led to some of us old guys that were at GM in the HEI development stages, to come back on,and get it figured out and fixed.
Failures were heat/load induced coil layer shorting to failure, and those issues causing HEI modules failing "for no apparent reason".
So, what did we do? Well, we simply reduced the spark plug gaps back down to the original .045 sizing, and, MAGIC, LIGHT OF LIGHTS, NIRVANA, THE WARRANTEE COIL/HEI MODULE FILURES/PROBLEMS AND FAILURES STOPPED, and failure rates went back to the levels pre-giant gap.
Opening up the spark plug gaps was done by a few brand name engineers, mostly at Olds, that dimply did not understand that the HEI will not tolerate giant spark plug gaps, it was an easy "fix" for a more sensitive fuel/air mixture developing situation, and their "fix" was totally WRONG..
Carburetor specifications were revised, emissions levels were maintained, and all was set good again.
Fact, We developed service bulletins, called FDM's (Factory Directed Modification) that REDUCED spark plug gaps on all those 4 division engines that were firwt set up to have the giant plug gaps, and, the dealers were instructed to pull all the plugs, regap if needed, ON NEW VEHICLE GET READY FOR SALE.
If yu still see a specification for an incorrect giant spark plug gap for an HEi for any of the HEI's, DROP THE GAP DOWN TO THE PROPER SPECIFICATION OF .045 MAXIMUM.
All this was done in the divisions that designed the HEI, here in America, NOT some place in the middle of the Gobi Desert, nor Antarctica, nor the moon, but, here in The United States, where it all started..
Those are the FACTS of it, if yOu have some sort of specification that insists on larger spark plug gaps in any HEI, it is WRONG, WRONG, WRONG.
This is an open forum, no problem there. If you disagree with these FACTS, I suggest you go investigate for yourself, as NONE of you worked with the team that fixed the problems, nor wrote the FDM's.....but, I DID.
