I'm just curious as to whether or not varying spark plug gap affects the lean/rich conditions of a motor?

What spark plug gap should I run with my 454 big block? I have been gapping the plugs at .044". I am only running an almost stock GM HEI distributor out of my old L48 350. It has an Accel distributor cap and rotor.

My plugs all read a tan color. Would it hurt if I gapped them closer to say .035". Is .044" gap too big of a gap with a stock distributor?

 

Sounds like they are gapped to big, try .040 and see if it gets any better. Your best bet, most likely, is to cut them back.

jm .02$

 

I kinda thought the gap was too big too. I think I'm going to try .035" and see what I get.

 

I would like to know a little bit more about this subject as well. Never hurts to konw too much! :thumbs:

 

dudeskie:
Did you figure out what was the matter with your motor? Have you taken it back to the track since the last time?

 

bence, have you tried sidegapping yet. i just did it today and it turned out good. Cars seems to run better. Side gapping is when you trim the ground electrode back so the tip just barely overlaps the center electrode. This is supposed to open up the spark area more into the combustion charge. With normal plugs the ground electrode kinda blocks the spark from getting ditectly to the compressed gasses. Ill try to get a link or a pic to show you what it looks like.

 

heres a pic of one I just cut back. I installed a new set of these cut back plugs today. Runs excellant. I gapped between the closest points to .040.

 

Jvette:
Thanks for the information. I may just give that a try. Currently my plugs are a pretty good tan color. I would however like to get them a little more tan then they currently are, possibly even on the verge of white would be nice. Norval runs his motor to the point that the plugs are white after a nice highway jaughnt.

I currently have the plugs gapped to .035" I'm going to see if that helps any. I am going to try what you suggested though. Thanks. :cheers:

 

sounds like a cool idea, never heard that one.. Is that old school???

 

Stock 454's with points etc are .035. Stockcoils don't have the oomph for larger. If you run a Crane, MSD, Mallory and the hotter coils gap at .045. Never tried the side gap or cutback.

 

Bence I was talking to my engine builder the other day about spark gaps. He just took an engine to PA to have it dyno'd there. He does some work with this guy and was curious how close his dyno was to one that we have here (was within 3-4hp :D ). Anyway, the guy in PA told him that he had experimented with plug gaps on the dyno and didn't see any advantages with going with gaps larger than the stock .035 .

My2C's :cheers:

 

Shane, I just got done doing some dyno testing yesterday on a 355/brodix -8 heads/Holley strip dominator/ full roller cam motor that the customer wanted to try different ignitions on. I tried a stock HEI, a pertronix Flame Thrower HEI, a MSD 6AL with Blaster 2 coil and a Joe Hunt magneto. Peak power with all 4 systems was between 538 and 541 HP, so all the systems are good but none are better than the others. The best plug gap was .028 with the mag and .035 with the other 3 systems. The motor was 13-1 compression so a lower compression motor may be able to handle a little more gap for best power.


I have never been able to show any difference in power on the dyno with side gapped plugs. It is one of those things that if you "think" it is better then it is better. Similar to it always feels like a clean cars runs better than a dirty car.

 

I gapped mine at .060. That's what the MSD instructions said to do. Are you talking about running an MSD coil with stock ign or were you factoring in a 6AL CDI unit too?

 

I was referring to the Crane unit with their PS-92 coil. I had a MSD that crapped out with the stock coil and the gap was .045. If .060 is what the MSD with their HP coil great. Do they stay clean?

 

If you are not experiencing missing, spark plug gap is not contributing to the very slightly rich condition causing tan instead of white plugs.
HEI can easiy jump .045 gaps.
Check with Lars about carb adjustments.

Personally, I'd rather run a bit rich than too lean.

 

Shane, I have gone with a gap of .045 with my setup. According to the MSD people they say go with .050 to .060 with their stuff. I tried last week with a gap of .055 and it seemed ok but no difference, so I went back to around .045+ With a stock HEI setup .040 to .045 should be fine. My plugs are slightly darker tan on the highway, around town pretty dark, but with my 850 4 corner carb I know its running rich. I have talked to few engine guys and I agree that I would rather be on the rich side than too lean. Keep up the good work at the track!

 

I run .045 gap with 50000 Volt HEI and MSD 6AL box...

 

A few days ago i had a great link that explained the sidegap theory. i searched the web but cant find it so ill try and remember some of what was said. Companies like Splitfire and Bosch have thier own fancy way of achieving the same effect. On a Splitfire the ground electrode is split which exposes the center electrode more directly into the chamber. On the Bosch platinum +2 and +4 plugs they have the ground electrode bend up away, and exposing the center electrode. Trimming and side gapping standard plugs has been a known trick of hotrodders for a long time. Now think of this. If AC or Autolite or whoever else made and sold a plug with a trimmed ground electrode and told you it was better for performance you would obviously see that you could make this mod yourself to a standard cheaper plug. Then they wouldnt be able to charge you $5 each for some fancy design. One note mentioned with sidegapping was that you could take advantage of smaller gaps. not quite sure what that meant. Another note mentioned was that side gapped plugs would need to be replaced more frequently since the spark has a tendancy to jump from and to the edge causing faster wear on those points. Most of us on here replace our plugs quite frequently anyway. Wish I could find that link.

 

To sidegap the plugs I first practiced on a couple of old plugs to get the feel. First bend the groung electrode back to help avoid hitting the center electrod with the cut off wheel. I use dremel cutoff wheels #426. These are the fiber type wheels. The all stone wheels seem to break up too easy. Rather then trying to cut off the perfect amount I cut them back some at first then bent the electrode down some to view the plug directly down from top. the idea is to have the ground electrode just barely overlap the center electrode, leaving the majority of the center electrode exposed from a straight down viewing. After the first cut, I used the edge of the cutting disc to grind the tip back to the perfect amount. then filed the burrs with a thin flat file or nail file and gap between the closest points. Make sureb to put the dremel tool on a slow setting since it doesnt take much work. If you look at the picture I posted in this same thread you,ll see that the ground electrode just barely overlaps the center electrode. Happy grinding. :D