Mod. 300 plug selection
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,188
Likes: 384
From: Near Los Angeles
Mod. 300 plug selection
Hey guys--
What type of s. plug should I run? I have a modified 300, mild cam, .030 over, p&p head with over size sbc valves, and the deck is shaved .020, like the head.
The engine is a '78, and the head is from an '81. I am running an MSD 6a ignition with an MSD TFI coil and recurved ds11 dizzy. After digging around here, I wanted to run a EFI plug, so I bought Motorcraft SP-435's (supposedly for an 89 300) for it. But they look like they reach 1/2" deeper into the chamber than the Champion RF18YC's which I took out of the head.
Does anyone know what is a good EFI (high energy) plug? And yes, I'll certainly check they clear pistons and valves! Thanks in advance!
What type of s. plug should I run? I have a modified 300, mild cam, .030 over, p&p head with over size sbc valves, and the deck is shaved .020, like the head.
The engine is a '78, and the head is from an '81. I am running an MSD 6a ignition with an MSD TFI coil and recurved ds11 dizzy. After digging around here, I wanted to run a EFI plug, so I bought Motorcraft SP-435's (supposedly for an 89 300) for it. But they look like they reach 1/2" deeper into the chamber than the Champion RF18YC's which I took out of the head.
Does anyone know what is a good EFI (high energy) plug? And yes, I'll certainly check they clear pistons and valves! Thanks in advance!
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
I use autolite 45s in every ford that uses the 18mm taper plug. 46 is hotter yet I use them when oil fouling is an issue. My 96 4.9 and my wifes 89 5.0 use 45s and that gives me great results.
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
The EFI plug is a cheap upgrade because of the extended reach. Really doesn't matter what the make. You can experiment with different gaps from 44-55 to see what your engine likes. Other than longevity, I don't see any benefit from the "precious metal" type plugs. I use the NGK V-Groove gaped at 50.
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,188
Likes: 384
From: Near Los Angeles
EFI plug clearance?
The EFI plug is a cheap upgrade because of the extended reach. Really doesn't matter what the make. You can experiment with different gaps from 44-55 to see what your engine likes. Other than longevity, I don't see any benefit from the "precious metal" type plugs. I use the NGK V-Groove gaped at 50.
Also, I'm trying to understand why being further into the chamber with the spark makes a performance difference. Could someone explain.
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
I don't think you have to worry about clearance. Some have used the EFI plugs with zero decked blocks. The difference, in very general terms, has to do with where the spark and flame kernel initiate from and how this may cause a cleaner, even burn in the combustion chamber. You might try first using the carbed plugs for a while and then switch to the EFI's to see what the difference may be. One person I know claims the switch to the EFI's caused his engine to idle faster (not a bad thing) until he readjusted the curb idle on the carb back down. Your results may vary.
