View Full Version : Plug Gap Recommendation
ProfessorB
08-15-2024, 05:11 PM
I've only owned this car a short while (bought an already completed car) and now I'm taking a look at engine tune. Motor is a carbureted 427 Windsor with MSD electronic ignition. Plugs are presently gapped at .035..... for comparison, what do y'all set your plug gap at?
Bill Elliott
08-15-2024, 05:14 PM
I have a 427 with Holley EFI gapped at .040 .
GoDadGo
08-15-2024, 06:10 PM
Professor,
What gap does your MSD ignition system recommend?
I'm running an HEI from DUI and am running .050 per the recommendation of one of their Tech Reps.
He said I could go as high as .055, but I'm maxing out my timing at only 32 degrees to avoid problems associated with fuel.
DUI LINK:
https://performancedistributors.com/product/chevrolet-streetstrip-dui/
Do you have any of the system documentation regarding your system?
Steve
Pat Landymore
08-15-2024, 08:01 PM
As I’m kind of a counter culture lad with a fixation on real data…I’ll throw the link to this video into the mix. It’s about 13 minutes but if you’re impatient…just scroll straight ahead to the last three for dyno verified data.
I’ve been hot rodding stuff for most of my 63 years…and I was rather surprised by how close the dyno graphs were at 0.010”, 0.021” and 0.100” plug gap.
Link here:
https://m.youtube.com/watch?v=_6qzd08D7ow
Hope it spurs some discussion!
Cheers
BornWestUSA
08-15-2024, 08:10 PM
From MSD:
Up to 10.5:1: 0.050" - 0.060"
10.5:1 - 13.0:1: 0.040" - 0.050"
Above 13.0:1: 0.035" - 0.045"
https://www.jegs.com/InstallationInstructions/100/121/121-6201.pdf?srsltid=AfmBOoqSh3it4lnqx0gkSecyt7PvByx7w g3aQimsxQl3tYd0mZ7cpVJc
ProfessorB
08-15-2024, 08:23 PM
Professor,
What gap does your MSD ignition system recommend?
I'm running an HEI from DUI and am running .050 per the recommendation of one of their Tech Reps.
He said I could go as high as .055, but I'm maxing out my timing at only 32 degrees to avoid problems associated with fuel.
DUI LINK:
https://performancedistributors.com/product/chevrolet-streetstrip-dui/
Do you have any of the system documentation regarding your system?
Steve
I have the documentation somewhere (but haven't been able to locate it). I "settled" on .045 so I could install the plugs. I DID do some online research (including the MSD website) and found information that matched yours. I saw that same figure (.055) but also read that the larger the gap, the more "stress" on the electrical components.... so I'll try .045 and see how it runs.
rich grsc
08-15-2024, 09:23 PM
No need for such a huge gap, .035-.040 is all you need. At higher rpm's, it's harder to fire the big gap
Here's some very basic food for thought. The spark begins at the coil, travels the coil wire and jumps the small air gap of the center electrode. Then it jumps the gap of the rotor to cap and finally jumps the plug gap. The wider the plug gap the harder that process becomes. The spark will take the path of least resistance often crossfiring in the distributor or arching at a plug wire weak spot. More voltage(msd)just makes it worse. So years of industry experience has shown that .030-.040 is the sweet spot. Boosted engines generally run tighter gaps. That's also an advantage of distributorless ignitions. It removes several paths for failure.
Bob
ProfessorB
08-21-2024, 01:27 PM
UPDATE: PLugs are installed, gapped at .045, and car has been road tested. (NGK brand plugs). Never ran better.
gbranham
08-21-2024, 03:11 PM
I love it. Asks for recommendations, then ignores the consensus. But, if it's running great, that's all that matters.
Jeff Kleiner
08-21-2024, 04:31 PM
I love it. Asks for recommendations, then ignores the consensus. But, if it's running great, that's all that matters.
When Bob L talks smart people listen ;)
Jeff
ProfessorB
08-21-2024, 04:35 PM
I love it. Asks for recommendations, then ignores the consensus. But, if it's running great, that's all that matters.
Well, NO offense taken with your comment but here was the "consensus":
.040 three votes
.050 one vote
.040 to .050 (for 10.5 compression which I have) one vote
Also, a few suggested a smaller gap is all you need (.035 to .040), and one comment provided a link which claims .010 to .100 made little difference. And finally... several websites suggested .045 to .055 for my particular ignition. I'm not sure that's a consensus. I considered ALL of the comments and went with .045...which is sort of in the middle. And I appreciated ALL the input. ALL of it helpful.