What is the best position to index spark plugs in the LS1? Should the open end of the electrode point directly toward the center of the intake valve, or might it be placed more clockwise than that? Upon teardown of my motor, I didn't notice any effort by the factory to address this.
Thanks, gMAG

 

"What is the best position to index spark plugs in the LS1? Should the open end of the electrode point directly toward the center of the intake valve"

Yes.

 

How are you going to index them?

 

Thank you Mr. Sanders!

 

Cal, The heads are presently off of the motor. Because everything is in view, it should be a straight shot using the proper shims. If the heads were already installed, I'd mark the exposed end of the spark plug coincident with the open electrode and then "see" how that mark lines up(or not) with the intake valve. Then, the correct shim could be added.
Hope I didn't misunderstand your question. gMAG

 

What are you using for shims?

 

Yup, that answers my question. I figured you would have to either add some metal somewhere or take some away. So are you going to cut some washers out of shim material, or is there a company that offers them made? Pop cans are a source of thin aluminum shim material if you're going to make your own. Sounds like a lot of work to make them though; I think I would be tempted to chuck up each plug in my lathe and remove some metal from each plug rather than add it with shims. After doing the first two you could even calculate the thousanths/degree of rotation to eliminate the cut & try system for the rest of them.

 

Scott, I'll be needing to buy some. You should be able to locate them at your local speed shop. The package will have 20 or 30 total, consisting of 3 or 4 different sizes. They can be made of copper, or a soft metal, and I've even seen them made of a nylon type material.
I think you'll find that most of the plugs will need only a very small rotation (smallest shim) to correct. And, of course, the maximum amount of correction would be half a rotation of the plug. I've never witnessed this much error, though.
Finally, I did a search on Yahoo for "spark plug indexing", and came up with this company. JC Specialty @ 570-837-0042 in Penns Creek, PA. You might also check with LS1tech sponsors.

 

Cal, If I had my choice, I'd prefer your idea using the lathe, over the shims. My subjective preference wants the plug deep, rather than shallow. Offhand, though, I'm not sure if placing a plug deeper (lathe) would cause any interference. Perhaps, it's not even an issue.

 

Thanks a lot!

 

I would index plugs by jockeying them from clinder to cylinder. You may find you dont need any shims or machining.Keep in mind any shims added will slightly raise heat range of that particular plug. Common rule of thumb practice is to aim plug gap at exhaust valve to promote more thorough combustion. Clipped electrodes and large gaps is where biggest power gains from ignition are found btw.

 

Forgive me if I'm wrong but I thought the plugs had a tapered seat not a flat seat with a washer. If they are tapered, then you can use shims. You would have to machine the head or the thread on the plug. The best idea is to swap them from cylinder to cylinder until you get plugs pointing towards the exhaust valve IMO.

 

I like your idea of swapping plugs.
However, the thought that led to my original question (proper orientation of spark gap), led me to believe that placing the open gap slightly away from the intake valve would be more advantageous than having the gap directly face the intake. Giving the swirl a chance to enter the chamber more fully made sense to me. There aren't many positions that one can rotate the plug toward, since the plug is at quite an angle. Moving it away from the intake valve causes the electrode to turn rapidly toward the ceiling of the combustion chamber. On the other hand, moving it toward the exhaust creates another question. Would THAT position be efficient? Gap toward intake encounters more of the swirl in the most open area of the combustion chamber.
All of your views are definitely food for thought!
Thanks, gMAG

 

Spark plugs are stupid

 

I see what gMAG is sayin and it makes a bit of sense to me... but that being the case, the *most* efficient orientation of the plugs would be different for each set of heads depending on how it's ported, etc... at least I would think. I mean stage 2 heads compared to my stock heads would flow a lot more and change the pattern of swirl inside the chamber.

On a side note, is there any way to do the indexing without taking the heads off the engine?

 

[quote]
Spark plugs are stupid [/quote
Yeah, For all of our efforts, it kinda makes you feel like there's a point of diminishing returns! gMAG
(how did my comments end up inside your quote?)

 

pimpmaro, Please see 5th item in this thread for plug indexing with heads on. Because the plug enters the head at such an angle (with regard to the intake valve), try to visualize how the tip of the plug is oriented toward the intake.

 

Hey Guys and Girls, For anyone still interested, I was checking out the relationship of spark gap and plug orientation in the cylinder head, with the heads removed. Here's what I came up with...
There is a plug position that can be achieved which favors the intake, the exhaust, and the combustion chamber, all at one time. In my opinion, any position other than this one favors the exhaust, or the intake, or shrouds the combustion chamber from an efficient spark.
There are a couple of ways to align the plug. The easiest is the following...
Place a line on the plug body which points to the spark gap. The spark plug hole in the head is angled. When installing the plug, make sure the line on the plug is centered exactly between the left border of the plug hole, and the right border of the plug hole. If the spark plug line is more left, you're favoring the intake. If it's right, the exhaust. I would tend to err on the intake side (line left),as this position also favors the combustion chamber.

After several tries at swapping plugs/cylinders, I was able to achieve a reasonable "match" with little error. And, after all, I discovered upon teardown that the factory had made no attempt at orientation. Anything more was an improvement!
Also, after rechecking, I WOULD VETO THE USE OF SHIMS! A shim will withdraw the electrode into the plug hole. This is NO GOOD!! First try swapping plugs/cylinders. If a reasonable match can't be had, I'd go for machining the BASE OF THE PLUG where it meets the head. You'll have to determine how much machining is needed, but, that's another story! Thanks, gMAG

 

Glenn, thank's for the heads up. This is an interesting thread; it really speaks to the engineer in me! Some may say the difference is small, but there will be a difference. In dual plug aircraft engines, it is standard practice to turn off one set of plugs and watch for an rpm drop to verify both manetos are working.

The plug swapping method is the best idea I've heard yet. If serious about this, you could even buy a whole Sh*t pile of plugs and sort through them for the ultimate match-up on each cylinder.

They are tapered shoulder design plugs, right? I've never had one out of my 2001 yet.

 

I don't think it would be that hard to determine how much to take off. You would figure out the relationship pretty quick from cut & try, but you could also calculate it easily from the the thread pitch. This method would be cheaper than buying a sh*t load of plugs, and not that hard if the plugs are made with the hex part concentric with the tapered seat. If not concentric, you could still do it but it would be a asspain centering each one with a dial mike and a four-jaw chuck.