Indexing LT5 spark plugs - ZR-1 Net Registry Forums

ghlkal · 02-07-2017

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 · 02-07-2017

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 · 02-08-2017

Quote:

Originally Posted by 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.

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

George Maz · 02-09-2017

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 · 02-09-2017

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 · 02-12-2017

Thanks George.

Useful information.

02-07-2017	#1
ghlkal Join Date: Jan 2012 Location: Wisconsin Posts: 887	Indexing LT5 spark plugs 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? __________________ 1990 ZR-1 #2180 Red/Black Many of the usual mods for 460HP, tuned by Marc Haibeck ZR-1 Net Registry Member #1548

02-07-2017	#2
George Maz Join Date: Dec 2014 Location: Long Island, NY Posts: 295	Re: Indexing LT5 spark plugs 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. __________________ 1990 ZR-1 #1587 1990 ZR-1 #1727

02-09-2017	#4
George Maz Join Date: Dec 2014 Location: Long Island, NY Posts: 295	Re: Indexing LT5 spark plugs 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. __________________ 1990 ZR-1 #1587 1990 ZR-1 #1727

02-12-2017	#6
ghlkal Join Date: Jan 2012 Location: Wisconsin Posts: 887	Re: Indexing LT5 spark plugs Thanks George. Useful information. __________________ 1990 ZR-1 #2180 Red/Black Many of the usual mods for 460HP, tuned by Marc Haibeck ZR-1 Net Registry Member #1548