Spark Plug Indexing
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Re: Spark Plug Indexing (Strick)
I recently polled for the same question:
http://forums.corvetteforum.com/zerothread?id=498726
I indexed the plugs in my '94 Dakota 5.2L (by playing musical plugs, didn't use indexing spacers) because there is tons of space to get at the plugs on it.
Some day when i'm really bored and haven't cussed, sworn, or thoroughly exercised my knowledge of profanity in a long time I might take a shot at *trying* to optimize the indexing of the NGK's in my LT1.
The indexing spacers are reputed to alter the heat range characteristics of plugs so I won't use them. Better to just play musical plugs and see which one indexes best, cylinder by cylinder... :cuss
[Modified by Lone Ranger, 4:28 PM 3/3/2003]
http://forums.corvetteforum.com/zerothread?id=498726
I indexed the plugs in my '94 Dakota 5.2L (by playing musical plugs, didn't use indexing spacers) because there is tons of space to get at the plugs on it.
Some day when i'm really bored and haven't cussed, sworn, or thoroughly exercised my knowledge of profanity in a long time I might take a shot at *trying* to optimize the indexing of the NGK's in my LT1.
The indexing spacers are reputed to alter the heat range characteristics of plugs so I won't use them. Better to just play musical plugs and see which one indexes best, cylinder by cylinder... :cuss
[Modified by Lone Ranger, 4:28 PM 3/3/2003]
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Re: Spark Plug Indexing (Strick)
Hey, check it out. I found this pic of an LT1 head, its an aftermarket but that doesn't matter. Not haveing seen the interior side of an L98 or LT1 head I wanted to see how the spark plug bore was angled, so as to visualize what would be the ideal way to index plugs. Here's the pic:
It is apparent that the only bad arrangement for spark plug to situated in would be when the backside of the ground strap faces downward towards the top of the oncoming piston which would tend to shroud the spark. Based on that theory, as long as the ground strap is out of the way enough to expose the spark to piston the plug is pretty much optimally indexed. Assuming the plug has the conventional L-shaped ground strap then it looks like the spark will be desireably exposed about 75% of the time even when no attempt is made to index the plugs. If you study the way the plug holes are angled into the head this becomes apparent.
So this would appear to be good news for LT1'ers, and probably L98'ers too (assuming plug bore geometry is similar L98 vs. LT1).
Somone jump in and slap me awake if I'm being stupid... :D
It is apparent that the only bad arrangement for spark plug to situated in would be when the backside of the ground strap faces downward towards the top of the oncoming piston which would tend to shroud the spark. Based on that theory, as long as the ground strap is out of the way enough to expose the spark to piston the plug is pretty much optimally indexed. Assuming the plug has the conventional L-shaped ground strap then it looks like the spark will be desireably exposed about 75% of the time even when no attempt is made to index the plugs. If you study the way the plug holes are angled into the head this becomes apparent.
So this would appear to be good news for LT1'ers, and probably L98'ers too (assuming plug bore geometry is similar L98 vs. LT1).
Somone jump in and slap me awake if I'm being stupid... :D
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Re: Spark Plug Indexing (Lone Ranger)
It is apparent that the only bad arrangement for spark plug to situated in would be when the backside of the ground strap faces downward towards the top of the oncoming piston which would tend to shroud the spark. Based on that theory, as long as the ground strap is out of the way enough to expose the spark to piston the plug is pretty much optimally indexed. Assuming the plug has the conventional L-shaped ground strap then it looks like the spark will be desireably exposed about 75% of the time even when no attempt is made to index the plugs. If you study the way the plug holes are angled into the head this becomes apparent.
So this would appear to be good news for LT1'ers, and probably L98'ers too (assuming plug bore geometry is similar L98 vs. LT1).
Somone jump in and slap me awake if I'm being stupid... :D
So this would appear to be good news for LT1'ers, and probably L98'ers too (assuming plug bore geometry is similar L98 vs. LT1).
Somone jump in and slap me awake if I'm being stupid... :D
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
Re: Spark Plug Indexing (Strick)
The only reason racer's ever indexed plugs was because with the really
big dome pistons, the dome could hit the ground strap if it wound up
in the wrong position, so the plugs were "indexed" to prevent this. This
was especially prone to happen on aluminum rod drag motors where
the rod would stretch as much as .050" at high engine speeds. There's
no performance benefit.
Dan
big dome pistons, the dome could hit the ground strap if it wound up
in the wrong position, so the plugs were "indexed" to prevent this. This
was especially prone to happen on aluminum rod drag motors where
the rod would stretch as much as .050" at high engine speeds. There's
no performance benefit.
Dan
Drifting
Joined: Feb 2003
Posts: 1,978
Likes: 2
From: San Antonio Texas
Re: Spark Plug Indexing (Strick)
:iagree: Some engines with hi-compression "pop-up" pistons would close
up the plug gaps if I remember correctly. I think it was a big
block problem mostly. I've heard of fuel wash problems too but
I don't know if this was legit or not. Any way your idea sounds
as good as any other....go for it!
up the plug gaps if I remember correctly. I think it was a big
block problem mostly. I've heard of fuel wash problems too but
I don't know if this was legit or not. Any way your idea sounds
as good as any other....go for it!
