plug recommendation

[Tom of VA]

Anyone have a spark plug type & gap recommendation for by newly built 428 with 10.5:1 and a MSD dist & 6AL ignition?
Thanks

[patrickt]

Your engine is very similar to my engine. I use Champion 426 (RC9YC5) gapped to .040 -- others will no doubt have different recommendations.

[Michael C Henry]

New Car Craft (March) pg 36 has an article about finding the best choice for plug design and temp range. I have yet to apply it myself. It's about five pages long.

[Naumoff]

Are you running Alloy or Cast Iron heads?

Cast Iron for Street/strip
Motorcraft BF-32
Autolite 35 or 34
Champion F-11YC or F-9YC
Accel 378

Aluminum Edelbrock
Motorcraft AGSP-33C
Autolite 3926
Champion RC-12YC
Accel 416

Gap Electronic 44
Point type 35

Hope this helps. This is for street and strip if you go full comp use a colder plug and a smaller gap.

[BOURRET]

Originally Posted by Naumoff

Are you running Alloy or Cast Iron heads?

Cast Iron for Street/strip
Motorcraft BF-32
Autolite 35 or 34
Champion F-11YC or F-9YC
Accel 378

Aluminum Edelbrock
Motorcraft AGSP-33C
Autolite 3926
Champion RC-12YC
Accel 416

Gap Electronic 44
Point type 35

Hope this helps. This is for street and strip if you go full comp use a colder plug and a smaller gap.

Mine: Alu Edelbrock heads
Plugs: Champion RC12YC
Engine: 482 FE alu Shelby block
Gap. .7mm

[lineslinger]

Naumoff
Why does the alloy of the head dictate a different plug, is it the heat retention of the alloy with which the head is made?
Does the multiple spark given by the MSD during the firing stroke have an influence as well?

[RedCSX1]

The Edelbrock heads take a smaller diameter plug. I run Autolite 3926 which is the most recommended plug for FE motors. Dyno test have shown that you gain nothing from a larger than 35 point gap. I have a 6AL box with MSD coil and distributor.

[Naumoff]

Originally Posted by lineslinger

Naumoff
Why does the alloy of the head dictate a different plug, is it the heat retention of the alloy with which the head is made?
Does the multiple spark given by the MSD during the firing stroke have an influence as well?

As Morgan said the Edelbrock Alloy heads have a smaller plug tap diameter.

Morgan, You are right about no HP gain for gap. With our engines running 10:1 compression or higher a smaller gap is fine. A larger Gap would be needed for a low compression engine.
The multispark is to make sure that the fuel in the cylinder fires. It is a better chance NOT to have a misfire in each cylinder.