1970 spark plug gapping

[Joe C.]

Re: 1970 spark plug gapping

I'll bet you .005" that it will make no difference.

Mike,

I've been meaning to ask you this for awhile. I heard that you knew the answer to this: Why did racers back in the day like to "short gap" their spark plugs?

To get to the other side? Dunno, ask Clem, he's old.

I already know the answer. I'd like to know if you do as well. Apparently, according to your post #8, you don't believe that widening the gap will make any difference. I disagree. The question is designed to determine if you feel the same way about smaller gaps as well.

When it comes to ignition systems, you remind me of Mr. Williams. You're both stranded in the year 1972, although his arrested development applies to all aspects of engine technology. His dissertations on camshafts, especially, are not always supported by thorough analysis.

Remember we are talking about 1970 technology, and a high compression engine, the ignition system can get a little marginal at high rpms. The stock class racers commonly closed down the gaps to ease the voltage requirement for high rpm operation. This was done in conjunction with other tips of the trade all aimed a maximizing the likleyhood that the mixture would get lit under a max performance situation. HEI and other modern ignition systems pretty much eliminated the problem, although not without other issues, so it's relavent to a question of "in the day"

Awwwwwwwwww..........now ya went and ruined it!

[Michael W.]

Re: 1970 spark plug gapping

Awwwwwwwwww..........now ya went and ruined it!

Umm, the OP mentioned nothing about 'racing'.

[Joe C.]

Re: 1970 spark plug gapping

Umm, the OP mentioned nothing about 'racing'.

You missed my point. The point is, is that spark plug gap size will make a difference in an engine's performance. With old technology (high internal resistance coils with external ballast, which are rated at 20 Kv), the short gap technique ensures that the spark plug fires on every cycle, albeit with a less energetic spark. Rich mixtures ignite more readily with a less energetic spark.

Extending that concept back to the original discussion, I had suggested that a more powerful ignition system would enable a wider spark plug gap, and that system came to be used beginning in 1975 GM vehicles. Known as HEI, it employs the same idea that more powerful aftermarket coils (low internal resistance without external ballast, and rated at 40-45 Kv) employ, and which you constantly rail against. With more voltage available at the spark plug, wider gaps can be employed. Because of the increased voltage, not only do the spark plugs fire consistently, but they fire with a more energetic (hotter) spark, to ensure better and more complete combustion. This also prevents fouling.

[William C.]

Re: 1970 spark plug gapping

That is why GM made the switch to HEI, partially driven by tighter emmisions regs, and HEAVY government penalties for emissions system failure. I fyou don't have an HEI system, you need to work with best practices from the pre-hei era, which have been discussed here.

[Michael W.]

Re: 1970 spark plug gapping

You missed my point.

No, just ignoring your attempts to pick a fight. Nice try though.

That is why GM made the switch to HEI, partially driven by tighter emmisions regs, and HEAVY government penalties for emissions system failure. I fyou don't have an HEI system, you need to work with best practices from the pre-hei era, which have been discussed here.

Another driving reason was the requirement for cars to stay with pollution regs for extended periods of usage. A misadjusted or worn out set of points can easily allow an engine to fall outisde of the limits. A set-and-forget electronically triggered system (HEI or not) precludes that variable. The vast majority of people here have stock or near stock engines and don't use their cars for racing. The standard non HEI ignition systems installed by GM up to 1975 work just fine given a bit of occasional maintenance.

[Joe C.]

Re: 1970 spark plug gapping

No, just ignoring your attempts to pick a fight. Nice try though.



Another driving reason was the requirement for cars to stay with pollution regs for extended periods of usage. A misadjusted or worn out set of points can easily allow an engine to fall outisde of the limits. A set-and-forget electronically triggered system (HEI or not) precludes that variable. The vast majority of people here have stock or near stock engines and don't use their cars for racing. The standard non HEI ignition systems installed by GM up to 1975 work just fine given a bit of occasional maintenance.

I'm not trying to pick a fight, Mikey.

I simply don't want any of the unwashed masses to buy into your mistaken belief that old technology ignition systems are "the best thing since sliced bread" and cannot be improved upon. New technology, and much improved ignition systems are not only useful for racing, and/or leaner burning engines. I wish I had a penny for every owner who complains about spark plug fouling, and whose problem was cured once the system was upgraded.

Yes, they work "just fine" but are marginal, at best. The slightest variation from ideal running conditions, especially as it relates to fuel mixture, would cause spark plug fouling as well as misfiring with consequent loss of power and economy (such as it was).

[Jim T.]

Re: 1970 spark plug gapping

On page 63 of the 1970 owners manual it is specified that 35 is the spark plug gap for all listed Corvette engines in 1970.

[Timothy B.]

Re: 1970 spark plug gapping

I'm not trying to pick a fight, Mikey.

I simply don't want any of the unwashed masses to buy into your mistaken belief that old technology ignition systems are "the best thing since sliced bread" and cannot be improved upon. New technology, and much improved ignition systems are not only useful for racing, and/or leaner burning engines. I wish I had a penny for every owner who complains about spark plug fouling, and whose problem was cured once the system was upgraded.

Yes, they work "just fine" but are marginal, at best. The slightest variation from ideal running conditions, especially as it relates to fuel mixture, would cause spark plug fouling as well as misfiring with consequent loss of power and economy (such as it was).

Joe,

I installed the breakerless se on my 67 and it's amazing how much cleaner the idle is with perfect dwell and not having to worry about point resistance problems I agree that the new technology is much better with HEI.

I disagree about Duke being stuck in 1972, I believe it's 1965 or so but that's probably not a bad thing given what's happening in todays world.

[Michael W.]

Re: 1970 spark plug gapping

Joe,

I installed the breakerless se on my 67 and it's amazing how much cleaner the idle is with perfect dwell and not having to worry about point resistance problems I agree that the new technology is much better with HEI.

I disagree about Duke being stuck in 1972, I believe it's 1965 or so but that's probably not a bad thing given what's happening in todays world.

I'm stuck in '73, just as a point of correction. Tim- you do realize that the breakerless se is NOT an HEI system. The output from the coil is same as with horse and buggy points.

[Duke W.]

Re: 1970 spark plug gapping

Joe,
I disagree about Duke being stuck in 1972, I believe it's 1965 or so but that's probably not a bad thing given what's happening in todays world.

Actually, it's 1963. I never got beyond AFBs and drum brakes.

Duke

[Timothy B.]

Re: 1970 spark plug gapping

Nothing wrong with AFB's and drum brakes..

Michael, yes I realize it's the same as points but I will report the occasional idle miss/skip is gone because no resistance like used points. The breakerless se is a nice add on if you get the chance to try one on your car.

[Michael D.]

Re: 1970 spark plug gapping

...stranded in the year 1972...

Stranded in the 70s. Isn't that the name of a movie?

[Michael W.]

Re: 1970 spark plug gapping

The breakerless se is a nice add on if you get the chance to try one on your car.

BTDT- see below

Stranded in the 70s. Isn't that the name of a movie?

Speaking of 'stranded' that's what one of the most well known breakerless systems did to me in the 90s- dead as a door nail, out in the middle of nowhere. Nice. Since it didn't make any difference in performance in the first place, I simply reinstalled the points and condenser and it's been that way ever since. I've eliminated most of the side and end play on the distributor shaft which is a leading cause of erratic dwell or miss at idle.

[Joe C.]

Re: 1970 spark plug gapping

BTDT- see below



Speaking of 'stranded' that's what one of the most well known breakerless systems did to me in the 90s- dead as a door nail, out in the middle of nowhere. Nice. Since it didn't make any difference in performance in the first place, I simply reinstalled the points and condenser and it's been that way ever since. I've eliminated most of the side and end play on the distributor shaft which is a leading cause of erratic dwell or miss at idle.

If, in the 90's, you used a Pertronics trigger, and likely the original Pertronix I unit, then although it relies on the Hall Effect as does the Breakerless SE, it is VERY susceptible to malfunction due to end play in the distributor shaft. Because of the design proximity of it's magnetic disc directly above the pickup module, if the end play becomes larger than the specified GM .002" - .008", then the Pertronix rotor can easily move too far away from the pickup module and cause a "failure to read". Pertronix specifies pickup-to-disc gapping of .010" - .040", and this is generally set when the shaft is seated due to gravity. Once the engine is started, any end play causes the shaft to rise until it takes up all of the end play. This consequence can easily cause the Pertronix magnetic disc to move out of range of the pickup.

The Breakerless SE is superior in all ways to the Pertronix unit, except for a single restriction.....................it does NOT permit one to upgrade to a more powerful coil and eliminate the ballast resistor without voiding the warranty. Coil upgrade/ballast elimination is possible with the SE unit, and the engineers at M & H, although noncommittal, never specifically verbalized any prohibition. Further upgrade to multi-spark-discharge can only be made after adding a power module such as a MSD 8910 to the negative side of the coil.

[Joe C.]

Re: 1970 spark plug gapping

Joe,

I installed the breakerless se on my 67 and it's amazing how much cleaner the idle is with perfect dwell and not having to worry about point resistance problems I agree that the new technology is much better with HEI.

I disagree about Duke being stuck in 1972, I believe it's 1965 or so but that's probably not a bad thing given what's happening in todays world.

Actually, it's 1963. I never got beyond AFBs and drum brakes.

Duke

Impossible! The LT1 camshaft didn't debut until 1970.