Indexing LT5 spark plugs

[ghlkal]

Does anyone index their plugs?

I was thinking about this because some of the new DI engines apparently require the plugs be indexed.

I don't know if it really provides any significant power increase, but since the plugs are so easy to get to and "see," I was thinking about doing it this coming plug change.

I assume I want the gap opening pointed "up" toward the intake valves, correct?

[George Maz]

Pointed completely open to the exhaust valve. The curvature pointed as much toward the intake valve, it "shields" the plug from intake mixture for a supposedly better spark.
I've been considering "side-gapping" a set of plugs for my next change. It's a lot of work for a minimal gain of 2-3hp. Side gapped plugs will need to be changed much sooner as only the one side of the electrode gets consumed, thus drastically reducing plug life.

Also, came across some information on wide gaping the plugs...just for reduced emissions testing. No idea if it actually works. In NY, we are emissions exempt for 1990 cars, but other states differ.

[ghlkal]

Pointed completely open to the exhaust valve. The curvature pointed as much toward the intake valve, it "shields" the plug from intake mixture for a supposedly better spark.

Hmm, I thought the spark should be "open" to the intake mixture. Obviously I don't know how to index a plug :p

[George Maz]

https://youtu.be/piJZ9_85ES8 watch at 18:50

Explains why you'd want to optimize clocking the plug to shield intake mixture from wet cooling it.

Indexing is particularly for clearance issues, no performance gains.

Aiming the curvature of the grounding strap toward the intake valve, so that intake mixture will flow rather than cause additional turbulent bump. (grounding strap tip points away from intake valve).

Replace all plug wire looms that are conductive (anodized, metal, chromed) for non-conductive ones. Avoid taping plug wires together.

[George Maz]

Pictures to get a sense of flow and area.
Intake blue flows to exhaust red
hemispheric head design, spark plug threaded hole in the middle of four valves (stock cylinder head)

...I'd be interested to seek some data on duty cycle of the injector sets, to see if it has any bearing on optimizing plug clocking...

[ghlkal]

Thanks George.

Useful information.

[Mr.Yuck]

I would love to see some real data from indexing spark plugs with the use of some kind of washer. Before and after readings from a five gas analyzer just at idle and at 2,000 rpm's to see the ppm (Parts, Per, Million) change of the HC,CO,CO2,NOX,02 this should show a leaner more efficient burn after indexing but without adding more fuel and changing the pulse-width and injector curve I would not think you would see any real horsepower gains.