installed (spark) plug depth - effect on combustion?
Thread Starter
Team Owner
Joined: Sep 2002
Posts: 22,209
Likes: 12
From: OBAMA IS HITLER
installed (spark) plug depth - effect on combustion?
I also posted this in the engine mods section.....
I have AFR (CNC'd with TPIS' program) heads, AFR says the plug reach required for AFR heads is 5/8" (.625"). I'm looking into using shorter header plugs, the Accels are .420", which is .205" shorter.
AFR says these are too short. TPIS says they're fine. Naturally, I'm confused.
What effect will .205" less depth have with combustion & performance?
I have AFR (CNC'd with TPIS' program) heads, AFR says the plug reach required for AFR heads is 5/8" (.625"). I'm looking into using shorter header plugs, the Accels are .420", which is .205" shorter.
AFR says these are too short. TPIS says they're fine. Naturally, I'm confused.
What effect will .205" less depth have with combustion & performance?
Melting Slicks
Joined: Oct 2000
Posts: 3,426
Likes: 4
From: Heidelberg PA
Cruise-In V Veteran
Originally Posted by comp
never leave threads exposed in combustion chamber For sure 
That is not what he is asking? If AFR recommends a minimum depth for the plug into the cylinder and the accels are less than the minimum there will be no threads exposed on either, but the accels will not stick as far out into the cylinder. How does this effect combustion?
Advanced
Joined: Jan 2000
Posts: 93
Likes: 0
From: Madera, CA
Plug Reach is the threaded portion
Are you talking about the plug's reach, the threaded portion of the body, or the length of the center electrode of the plug? These aren't the same thing. If the plug's reach is too short it will expose the threads in the head, which comp pointed out correctly is bad. Exposed threads can serve as hot spots and can increase the likelihood of detonation.
Now if the unmodified AFR head uses .625, but if TPIS's CNC program cuts into the plug boss in the chamber making it shorter, then TPIS's recommendation may be correct. Confirm this them not us.
Now if the unmodified AFR head uses .625, but if TPIS's CNC program cuts into the plug boss in the chamber making it shorter, then TPIS's recommendation may be correct. Confirm this them not us.
