MSD plug gapping...

[Rick Lee]

While I have things apart for a valve adjustment, I'm wondering how I should have my plugs gapped to best utilize my MSD 6AL. What's the biggest gap anyone's gotten away with in an SC?

[jdowty3]

I run at .040 with a MSD 6A and a Blaster SS coil.

[Jim Richards]

I went to the MSD website and found their tech forum. Here's what a search turned up (posted by msdtech16):
"These examples are just starting points to get you going in the right direction. Every application is different and should be tested and tuned:
Compression Spark Plug Gap
Up to 10.5:1 .050 - .060
10.5:1 – 13.0:1 .040 - .050
Above 13.0:1 .035 - .045"

I think I'm using ~ 0.050" on my 2.7RS engine.

[Rick Lee]

I have no idea what the compression ratio on my SC is. I have 964 cams and SSI's in an otherwise pretty stock US spec. 3.0.

[Paulporsche]

.045 for mine w/ 10.3-1.

[}{arlequin]

RL, you're definitely under 10:1

either stock 9.5:1 or possibly euro 9.8:1
if it was over 10, you'd need twin plug

[Vipergrün]

I have 050 on my SC motor with blaster coil and Magnecor wires

[kucharskimb]

on one of the plug manufacturer's websites, it said going beyond .045" was tricky. something about the shortest distance from the electrode to the ground started moving along the curve of the ground tab. so even though you have a .060 gap at the tip, it will actually arc further down the tab, and you will get a shielded spark.

so i guess to do it right, you would have to make sure the closest point is over the center of the electrode.

i run .045". compression check is 167psi, which i think is about 10:1...

[randywebb]

Electricity will follow the path of least resistance. As the gap increases the resistance to 'jumping' that gap increases (there are other complications, but...). Thus, the electricity may follow some other path to ground...

[jstobo]

In my 69 with JE 9.5:1 Pistons i tried .040. Had a high RPM miss starting about 6000rpm. Made sure carbs were set but miss remained, then regapped plugs to .035. Miss eliminated. Stock on my engine is .014 so it is much wider than stock. I believe stock on a SC is .024. I would pick a gap and try it. Then keep experimenting with it until you have the setting that works best for your motor. Wire resistance, dist cap condition, rotor all play a role in how big a gap you can run. Have fun.

[Rick Lee]

Just wanna confirm the gaps you guys have given are in inches and not mm. Right?

[}{arlequin]

yep. inches.

(american product=msd=std measurments)
it's the same reason pertronix mounting hardware is a pita to install in the field when all you have is metric tools, but i digress....

[Rick Lee]

Cool. I'm doing the world's slowest valve adjustment. Dumped the oil and got her all jacked up yesterday. I even got the upper valve covers off. Tonight my big accomplishment was removing the lowers and checking the head stud barrel nut torque values. I think I may remove the dizzy cap tomorrow. I just need to get her done before the Riesentoter DE in two weeks. Time for another glass of Maker's Mark.