My 1970 455 has MSD 6 AL box with MSD distributor electronic ignition.
I was wondering if the spark plugs were gapped

correctly at 35 I thought it’s supposed to be 45 with electronic?

 

I think MSD usually recommends .035 MSD is not the same as GM HEI which usually specified larger gaps.

If it runs good, leave it alone

 

Agreed, but two totally different ways of firing the plugs.

 

it runs pretty good. I honestly thought MSD was electronic ignition. I thought maybe the guy made a mistake I believe you guys.
well, I got them at 40. I did have a problem with the car running on a little bit like it needs higher octane than 91. Not sure if it has domed pistons, but sounds pretty Cammed.

 

X3. You could tighten it up a touch if it's higher compression, like 11 or 12:1, but you'll be fine at 035. Bigger gaps just stress components.

 

ok thx 35 it is

 

I think the plug gap would be more dependent on the coil used than anything else.

 

x 2

 

Msd blaster II

 

Tighten it up to 032 or 030 if it makes you feel better, but you're still good in my opinion

 

I run my 6al and blaster coil at .035.
Runs good. You may have to play with heat ranges.

 

You can get away with the stock gap of .030 - .040

 

Hmmm not really. It’s the compression ratio, the fuel you’re igniting and the total amount of current available, from the coil AND the box, normally measured in millijoules.

 

thx for all the input, going with 35 where it was.

They were burning light brown at 35. i just thought they should have been at 45 with anything better then points.Atleast thats what was rule of thumb all these years.

 

Spark plug gap is a function of the engine parameters and the coil voltage. People who weren't around when HEI first came out don't realize that GM went to much larger gaps on the factory HEI systems to comply with EPA requirements. Cars had to be able to meet emissions requirements after 50,000 miles without a tuneup (because owners really suck at basic maintenance). The large gap was selected to allow crud to build up on the plug electrodes without bridging the gap. The higher voltage was partly required to jump that larger gap. There's no real performance benefit to going larger than the gap needs to be.

 

You were probably fine where you were