Indexing spark plugs?

[sammerdog]

None of my buddies do it. They think I'm nuts. My Dad always did it as I held the flashlight for him when I was a kid, so I've always done it. He always got a lot of miles out of his Chevy Vegas and Monzas.

Do you guys do it?

For you young whipper snappers - indexing plugs is where you install them so the open gap winds up pointing down in the cylinder after installation. Usually, you make a black stripe with a Sharpie on the opposite side of the ceramic.

 

[little d]

we did it when we raced, but i never did it for a streat car. the hp gain was questionable, but with high dome pistons, ya would get a little better burn. we would also cut a burn groove in the top of the piston, this also seemed to help.

 

[wfopete]

Probably will depend on the motor in question. If this is a modern day engine, say mid 90's or newer, with today’s ignitions and head designs, the heads are probably pretty darn good when it comes to chamber burn efficiency. Still you can ask a motor builder for thoughts. I ain't one.

 

[rasit]

Yeah I do it on my 1982 Shovelhead motor. That engine is like a locomotive, practically bullet-proof if tuned properly so I do every thing possible to keep it in top shape, including indexing the plugs.

 

[robin1731]

I'm with little d. I do it on the race motors but I wouldn't take the time to do it on a street car. Not woth it at all IMHO.

 

[35mastr]

Never have. Dont see why it would even matter unless on a built specialty motor.

Spark is spark. The motor does not care which way the plug is installed. Other than it just wants spark in that cylinder when called upon.

 

[lilredex]

Do it on my snow blower.........makes it throw twice as far.........

 

[knucklebusted]

I did it once, took three sets of plugs to get all the cylinders done and made 0 difference in my ET. Thankfully, I could return two full sets of plugs.

 

[adam728]

I don't do it, and without a dyno to test different configureations I don't see the point to it. You can pick up a slight amount of power, but every engine, head, cam, operating speed will be different. One setup might benifit from pointing the open end at the intake valve, another at the exhaust valve, and another right in between.

 

[krooser]

More hocus-pocus unless you see the results on a dyno...

 

[RIVERWEST AUTO]

yeah, newer cars have individual coils anyway, diff voltage from each, every fire time. better off replacnig o2 sensor every month!

 

[regguy1]

Never have. Dont see why it would even matter unless on a built specialty motor.

Spark is spark. The motor does not care which way the plug is installed. Other than it just wants spark in that cylinder when called upon.

I agree:

Hum...if I threw a match in a can of gasoline, what would make a bigger explosion...if I had the match facing up....or down

I think the primary benifit is psycological for the mechanic.

 

[belvedere]

More hocus-pocus unless you see the results on a dyno...

+1. For those who believe in it: any proof of benefit, such as dyno results? I can't imagine it making any measureable difference.

 

[Brian41]

I tried this 2 weeks ago on my dyno with no proof that it made any more power, even went as far as to adjust timing on all cylinders to match and did not pick up enough if any to go through the trouble. This was on a 750 HP marine engine turning 5900 RPMS.

 

[iagsxr]

When I raced circle track a guy that had worked for a couple NHRA Pro Stock teams helped me w/engines. What he told me; no real hp, makes the plugs easier to read if they're indexed. Depends on the combustion chamber design as to how much that matters.

We have an old Champion benchtop sparkplug tester. If you watch what the spark does under pressure having the plug aimed right has to make for a happier chamber. I sometimes index plugs in my own stuff, but only use one box. Every plug finds a hole.

 

[toolmiser]

I remember an eppisode of "two guys garage" a few years ago where they idexed them. They had a special washer they would ad to get it where they wanted it. I don't remember anything else.

 

[redneckprofessor]

When I raced circle track a guy that had worked for a couple NHRA Pro Stock teams helped me w/engines. What he told me; no real hp, makes the plugs easier to read if they're indexed. Depends on the combustion chamber design as to how much that matters.

We have an old Champion benchtop sparkplug tester. If you watch what the spark does under pressure having the plug aimed right has to make for a happier chamber. I sometimes index plugs in my own stuff, but only use one box. Every plug finds a hole.

I took a performance engine building class, and you touched on the two points I remember being said about indexing plugs. First, it's helpful only if the engine sees high rpm. The idea is that you don't want the grounding strap to "shield" the spark from the combustion mixture and slow down the flame front. But, hard to verify real results, so it's questionable. Second, it makes reading plugs easier, more consistent.

I wouldn't bother on a street car or even a souped-up street car. Race car . . . well, I'd take all the help I could get.

 

[Toolhorder]

I agree:

Hum...if I threw a match in a can of gasoline, what would make a bigger explosion...if I had the match facing up....or down

I think the primary benifit is psycological for the mechanic.

Neither? The gas would put out the light unless it ignited the vapors above it first.

 

[robin1731]

+1. For those who believe in it: any proof of benefit, such as dyno results? I can't imagine it making any measureable difference.

There is no measureable difference. We do it because when you are sqeezing as much compression as you can, sometimes you get the dome right into the chamber and the tolerences are very close. You need to index the plug to keep from pinching the gap closed. At least on an old KZ style motor. Because of the angle of the plugs and the valves.

 

[Fubar]

Yeah I do it on my 1982 Shovelhead motor. That engine is like a locomotive, practically bullet-proof if tuned properly so I do every thing possible to keep it in top shape, including indexing the plugs.

Second that. I have a set of Zodiac dual plug heads on my 78 Shovel and it makes a difference...

 

[rsanter]

only even did it on racing engines.
you would need a good dyno to see any difference and it could only be worth doing when you are chasing that last little .1hp from that engine.
I always did it because it would take one variable (dis-similarity) out of the mix.
also when you are boilding a engine using pop-ups or a stroker engine the added clearance may be just what you need on some engines.

for the effort it takes, why wouldnt you do it

bob

 

[10.5 outlaw]

I've been tuning on all sorts of race engines over the years,The only time
I index plugs is when the piston has very little clearance to the cylinder head.
I don't do it on our 800 inch motor,i find it makes no differance.