View Full Version : PLug Gap?

05-16-2010, 12:22 PM
Hello I installed a 6AL-2 AND Dist #8543(Mech no Vac) I think thats the number Its on a Duster 340 4 speed 10 1/2 Pistons fairly healthy cam 3.73 gears 750 Holley. Been messing around with tuning the Dist(Springs) and going fairly well been dealing with preignition but just about got it. But reading about plug gap seems to be all over the place some say leave at .035 some say more. What does MSD suggest? Engines about 300hp thats by trap speed time in the car. I pulled a plug and it was about .035 maybe a little less even guessing they are about the same. Sure I read somewhere tight gap can cause preignition? These were gapped before the MSD was installed. D

05-18-2010, 04:39 PM
Information taken from Wire Diagrams and Tech Notes:

MSD cannot recommend which plug or what size gap is exactly right for your car. It is recommended to follow the engine builder’s or manufacturer’s recommendations for plug heat range and gap. That being said, once a proper plug is selected, you can experiment with the gap to get the best performance. By using these recommendations as a starting point, you can experiment by opening the gap in 0.005” increments then test. When
the performance falls off, the gap is too large. Carbureted or fuel injection engines can use larger gaps, but turbo or supercharged engines should stick with the smaller gap. If no significant gains are achieved, go with the smaller gap. Remember, the larger gap taxes the plug, wires, cap and rotor.

Rule of Thumb Plug Gap
UP TO 10.5:1 .040 - .045
10.5:1 - 13:1 .032 - .040
OVER 13:1 .025 - .032

Hope this helps,

MSD Admin

07-01-2011, 11:30 AM
I run .050"-.055" on my 302 mustang with no problems. .030" for nitrous. you have a strong system, so you can open up the gap a bit. try .010-.015 beyond what you ran before the MSD install. .040"-.045".. look at what the gap was on the later electronic ignition 360's, go from there.