Good Morning All,

So I bought this '73 Toronado that has a later HEI distributor and the specs call for a plug gap of .080.

Not being at all familiar with this application I would like to ask if the .080 is really optimum, and what the best plugs might be for this application.

It is a 455 that I think has the original low -compression setup of the era.

TIA,

David

 

One of the advantages to HEI is the capability of a wider plug gap which equals a hotter spark. I see no reason why the factory plug gap for the resistor plugs specified for the later 455 should not be used.

 

Turns out it is an Accel Hei unit if that makes any difference.

That gap on the installed plugs looks to be around .050, but I have not checked them all yet.

The ones I checked look new, but rusty on the outside from sitting and the color on them looks good.

 

I would not run an .080 gap, stick around .045.

 

Back when I was tuning for a living, what I would see is plugs with factory gaps of .080 would wear quicker. If I remember correctly, in some cases the factory gap was actually recommended to be changed to .060.

Mostly, though, the characteristics of the head will be more of a determining factor. Are the .080 specs you are referring to meant for the HEI or the original engine tune specs? I don't think the HEI came out until 1974, did it? If this is the case, I would start at .045 (a pretty standard HEI gap), and you could open it up incrementally over time to see if there are any issues with a wider gap - mileage or power loss, ping, whatever.

Generally, I wouldn't go above .060.

 

That's not true. A "hotter" spark comes from an ignition system with added millijoules and a wider gap. Just widening the gap could very well make the spark weaker if at that point the ignition system is at it's limit.
And the "extra" wear on the plugs at the .080 gap is due to a fairly hot plug and very lean mixtures.

 

My 76 olds 350 smog motor also calls for the .08 gap with # 8 heads. I myself have never played around with smaller gaps, It seems to run good with the factory gap specified. I guess I should be look at gaping them to .045 in the spring.

 

Maybe hotter was not the right word but a coil will produce only enough volts to jump a gap. My thinking is a wider gap requires more volts which yeilds a hotter spark or more millijoules?? If a coil is not strong enough it will not be able to jump the gap but once it does I dont see how it could be weaker. This is what was explained to me in Auto shop many years ago and I believe it is correct. No expert here just relaying what was told to me by someone with more knowledge than I. When you talk about millijoules I am lost.

 

X2 Erinyes, IIRC around 1985 it was recommended that the gaps be reduced to .060 to help with starting in very cold weather.

 

I too would go with no more than .060. Also try to select a plug that's designed for that gap, or pretty close to it (gap changes of more than .015 or so from what the plug was designed for is not a good idea imo). As for the .080 gag, GM revised this spec. down to .060 on some of their late '90s and early '00s Vortec plastic bodied distributor equipped trucks, SUVs, and full sized vans (which were notorious for eating ign. rotors, caps, wires, and ign. coils). I reduced the .080 gap on my 00' 4.3 Silverado down to .060 and actually noticed slightly better starting, power, and mpg (however, I used older non-platinum style plugs of the proper heat range and size that allowed a re-gap to .060).

 

The swirl port 307 went to .060", different plugs and combustion chamber. We ran our 81 Delta 88 with the .080" gap years ago. The plugs were a bit worn, not enough spark to jump the huge gap one damp morning. As long as it is checked and regapped maybe once a season, .080" will work fine. I personally run around .050" in my Olds powered vehicles. I know one member tried .035" and his car would barely run. Pretty sure the big gap was emissions related.

 

Millijoules is the total energy at the plug gap.
http://www.thefreedictionary.com/Millijoule

 

I run .080" gaps with no-name aftermarket HEI on my daily driver with a '71 350 in it. Has worked just fine the last 2˝ years/15000 miles.

 

Thanks, All!

I compromised on an .050 gap and all is well, at least here in Massachusetts where it is 40 deg.

I am delivering the beast to the mountains today, about a 230mi run.

I did test it with a 100mi round trip to the shipyard where I work yesterday and it never skipped a beat. (pause to knock wood)

After this it is up to the kid to keep it running. I'm glad to get the garage space back and get back to working on the '66

David

 

When determining an optimum plug gap one factor is spark duration. all else being equal the electrical energy generated by the coil will pass across the plug gap at a higher voltage but for a shorter period of time if the gap is increased.
A short duration spark may cause misfiring at high engine speeds, particularly if the combustion chamber has poor swirl characteristics.
A spark only needs to be hot enough (voltage+time) to ignite the fuel/air mixture. Less is required for a low speed, low compression 14:1 mixture than a high revving, high compression lean burn engine. That's why you garden tractor has a small magneto firing across a small plug gap and modern cars have high powered ignition systems to fire up the aneamic excuse we have for gasoline nowadays.

Roger.