Spark Plug -

[vso737]

What is the best spark plug to use on a 1972 400CI motor with Comp 268 high energy cam; 346 casting heads; Edelbrock performance RPM intake; 3310 Holley 750 cfm carb; and MSD Street Fire ignition.

Also, what should the spark plug gap be.

Attached are pictures of the Autolite AP 85 spark plugs I'm removing. They are gapped at .055

By the look of the plug, should I be using a HOTTER spark plug.

As always, I want to thank you in advance for any/all suggestions.

LG,
Mike

 

[Russ69Runner]

I am running NKG plugs in my 383 motor. 30 or 40 gap. Believe it is stated in repair manual in manuals on this site. Plug should be tan looking. Don't know if you are running too rich on the fuel air mixture or burning some oil. Need pics of the car.

 

[vso737]

I am running NKG plugs in my 383 motor. 30 or 40 gap. Believe it is stated in repair manual in manuals on this site. Plug should be tan looking. Don't know if you are running too rich on the fuel air mixture or burning some oil. Need pics of the car.

Thanks for your response.
I decided to go with a hotter plug and installed AP 86 with a .050 gap.
I last replaced the plugs April 2017 and have not put too many miles on the car. I'm pretty sure the plugs indicate carb running too rich rather than an oil issue. This motor has less than 5K since being rebuilt.
One thing for sure. all the plugs I removed looked exactly the same and were gapped at .055
I'm running 10:1 compression and read that the setting for an MSD electronic ignition setup should have a spark plug gap between .040 and .060 thousandth.
The full Hooker headers sure make changing the plugs a challenge.
I plan on pulling a plug after I put a few miles on these and see what they look like.

(paid $6.30 for a gallon of regular yesterday- for my Nissan pickup)

Thanks again,
LG,
Mike

 

[Russ69Runner]

It is also a heat range thing for the plugs. I have pop up pistons in my runner and had to go with a shorter electrode due to piston strike. Yes, it did look like fuel burn on the plugs.

 

[69hemibeep]

Looks a little fat to me!

 

[vso737]

It is also a heat range thing for the plugs. I have pop up pistons in my runner and had to go with a shorter electrode due to piston strike. Yes, it did look like fuel burn on the plugs.

YES, for quite some time now my wife shuts the front door and turns on the ceiling fan and lets me know how much the car is stinking up the house when I first start it. She's a lot more sensitive to the carburetor smell than I am........................................LOL
I may be visiting the carburetor once I put a few hundred miles on these plugs and change the spark plug wires on this monster. Don't expect to do any of it until the beginning of next year.
I have to split up having all of this fun with my other two classics.....................................LOL

 

[Terry Hauck]

This is a cool chart.

 

[SomeCarGuy]

Looks like you need to send the car to me. I’ll have it tuned up in a few years. That way you won’t have to worry about it.