Topic: Indexing Spark Plugs

[Tintop]

I can get indexing washers for the plugs I'm using (NGK Iridium), so...... question is does this work, and if so, what's the best position to aim for.

I've marked my plugs for the position of the ground.  Figure it should be facing the exhaust port.  Comments, suggestions.

[Sam Green Racing]

Brian, are you talking to aid travel of the flame path?

Sam.

[Tintop]

Yes Sam.  When I checked the plugs after the 'test & tune' I noticed that although similar, one appeared better than the other.  I marked them before removal, and noticed that the ground was is in different positions relative to the intake valve.  There was also a small 'rich shadow' area on both.  Tried to take pics, but camera won't focus that close / small.

Plug indexing is 'old school', but anything to help in getting complete / better combustion can't hurt.

[bwaller]

Brian, on the dyno last year after ignition testing I tried three different plug positions. (took a while to prepare first with different thickness indexing washers) No gain.

I have read all sorts of ideas on positioning, ultimately the people I trust most said there was nothing to be had, they seem to be right. In the end I still index the gap as closely as possible to the center of the chamber, between valves, so they're all the same.

Perhaps a bigger chamber would yield some gain, certainly it did not in the 550.

[Tintop]

......I still index the gap as closely as possible to the center of the chamber, between valves, so they're all the same......

That's the gap position I felt would be right, neither is there at the moment.  One's facing the intake valve, the other the exhaust.  The one facing the intake had a tan ground, the one facing the exhaust was darker.  That's what caught my attention, hence the indexing question.

Knowing that their firing the same way, takes gap position out of the equation when 'reading' the plugs.  Wasn't expecting any measurable gain from this.  Just want to remove a variable, but do it the most effective way.  There's other areas that I can work on later, that will produce HP (like a thinner head gasket).

[Sam Green Racing]

Something to be going on with, I'll get back with my take on this later.

Sam.

A matter of some debate is the "indexing" of plugs upon installation, usually only for high performance or racing applications; this involves installing them so that the open area of the spark gap, not shrouded by the ground electrode, faces the center of the combustion chamber, towards the intake valve, rather than the wall. Some engine tuners believe that this will maximize the exposure of the fuel-air mixture to the spark, also ensuring that every combustion chamber is an even in layout and therefore result in better ignition ; others, however, believe that this is useful only to keep the ground electrode out of the way of the piston in ultra-high-compression engines if clearance is insufficient. In any event, this is accomplished by marking the location of the gap on the outside of the plug, installing it, and noting the direction in which the mark faces; then the plug is removed and additional washers are added so as to change the orientation of the tightened plug. This must be done individually for each plug, as the orientation of the gap with respect to the threads of the shell is random. Some plugs are made with a non-random orientation of the gap and are usually marked as such by a suffix to the model number; typically these are specified by manufacturers of very small engines where the spark plug tip and electrodes form a significantly large part of the shape of the combustion chamber. The Honda Insight has indexed spark plugs from factory, with four different part numbers available corresponding to the different degrees of indexing to achieve most efficient combustion and maximum fuel efficiency.

[Tintop]

Thanks for posting that explanation Sam.

The two issues that you mentioned, and I'm trying to cover off are - maximizing spark exposure to the mixture, and having the same layout in each cylinder.  Piston clearence is not an issue, at least not at this point.  So the question is should the ground electrode be at 90 degrees to the intake & exhaust valves (bwaller's positioning), or more towards the exhaust valve, so the gap is more open towards the intake?

[bwaller]

Considering how much pressure & heat is in that chamber at the moment of ignition spark and we probably don't need to worry much. Try to find a common position is wise methinks. Here's a project for you...is there any way to add a second (even smaller would be good) plug? Henning did on the 450 heads so it might be possible on the XS too.

[Tintop]

Humm....a 2nd plug would be interesting.  However given the head layout (SOHC) it would be buried inside the rocker box.  I'll look at the spare head, but don't think it possible because the top end oil lines are were you'd want to put them. 

So given the discussion (and thanks for chiming in) here's the plan.  Right cylinder (from above) - intake is at 6 / exhaust at 12 / plug at 3 on ~ 40 degree angle.  The gap will be facing up into combustion chamber, and ground downwards into bore & centered between the valves.  Leftside plug is at 9 and I will orientated gap the same.

First race is in 17 days, we'll see then if this amounts to anything.

[brooze72]

I have nothing to add technically, but am enjoying the discussion & surprising myself by mostly understanding the concept.  Sam's revelation about the Insight seems to say Honda believes there is some credence to the indexing idea, guess there would be nothing to lose by doing it Brian.  I'm interested to hear what Bear might have to say.  Don't think I can make it to the track until Mosport in Aug, but you never know...  Best of luck this year, Brian & Brent (I'm following the sprocket/swing arm saga too!)
Bruce

[bear]

I have nothing to add technically, but am enjoying the discussion & surprising myself by mostly understanding the concept.  Sam's revelation about the Insight seems to say Honda believes there is some credence to the indexing idea, guess there would be nothing to lose by doing it Brian.  I'm interested to hear what Bear might have to say. 

Sorry gentlemen I don't have a lot to contribute.
Other than to say that we did give plug indexing a go for awhile.
But did not notice any change to performance or our plug readings.
One things for shore though, it an't gunna hurt.

Cheers,
Brian

[joe p]

I try the plug indexing thing. It just wasn't worth the trouble for me.

[MRieck]

I tried it too....I didn't notice any change. There may be some benefit on offset plugs like the 750, 550 etc but in a chamber with a central plug I cannot see any benefit at all. I had more off a change with filing the ground strap on conventional plugs

[Tintop]

I'm in the 'probably won't see any change, but can't hurt' camp.  Seems like this is something that probably has good results in a Top fuel, or Funny Car.  However, given our much smaller displacement / power output, any improvement is to small to register.

I tried it too....I didn't notice any change. There may be some benefit on offset plugs like the 750, 550 etc but in a chamber with a central plug I cannot see any benefit at all. I had more off a change with filing the ground strap on conventional plugs

Humm....interesting comment Mike.  There's a discussion on another forum re plugs for an RS250 GP bike.  They are NGK's with a very thin ground strap.  Might look into that later, and see if they are available in the right size / heat range for my application.

[Sam Green Racing]

Look at it this way, why are race plugs constructed the way thay are ?
For one, the ground electrode can't come into contact with the piston and two, the horizontal spark is not sheilded by anything so with these plugs, no indexing is needed.

Some years ago (I normally do my own) I had a head ported by a head specialist.
I wanted a Serdi valve job doing on it so trusted him to do the porting as well.
When I went to pick it up, he told me he had done a small mod that I hadn't asked for but there was no extra charge anyway.
What he did was to grind a small chanell between the plug holes and the inlet seats and told me to index the plugs so that the open end faced the center of the inlet valve. I didn't ask why, he just told me to trust him and I have always indexed my plugs that way ever since.

When we ask does it make a difference, I look at it like this, It's free and if it does in fact make a difference, several of these little differences might make a horsepower. Look how much you spend on Ti, Magnesium and alloy just to get that little bit of an edge.

Sam.

[Tintop]

.......I look at it like this, It's free and if it does in fact make a difference, several of these little differences might make a horsepower. Look how much you spend on Ti, Magnesium and alloy just to get that little bit of an edge.

Sam.

That's my feeling Sam. Why not, can't hurt.

[turboguzzi]

nice theory sam, only snag is that spark occurs like half an hour after the inlet has closed

TT, want a cheapo race plug? chop off about 1mm from the ground electrode so that it stops above the the center electrode at the center, spark will be more exposed.  not that i think it'll make a change either but makes you feel smug.

[Sam Green Racing]

This from NGK (they make spark plugs  )

Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.

However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.

In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.

Sam.

[turboguzzi]

ok, got it. next time i'm around the pits of Motogp or WSBK (last weekend at monza was cool, but too late ) will ask the mechs if they index.... thought these things have so much power which is capped off by electronics that they might not even care!

[POPS 911]

On a NHRA PRO-STOCK SUZUKI 2-VALVE MOTOR the plugs do not have any strap or extended electrode = flat bottom plug. NO INDEXING.

[Sam Green Racing]

Look at it this way, why are race plugs constructed the way thay are ?
For one, the ground electrode can't come into contact with the piston and two, the horizontal spark is not sheilded by anything so with these plugs, no indexing is needed.

Sam.

[NitroHunter]

Seems like this is something that probably has good results in a Top fuel, or Funny Car. 



Our 44 amp mags pretty much take care of those pesky indexing issues. 

[MRieck]

Seems like this is something that probably has good results in a Top fuel, or Funny Car. 



Our 44 amp mags pretty much take care of those pesky indexing issues. 

Top Fuel burns the ground strap off.....in one run.

[Don R]

5hp in a pro stock drag car is .02 ET. That's a pretty good gain.  On my dragster the piston can hit the ground strap. I've always indexed them anyway. Takes a few minutes and can't hurt. A friend uses the washers to keep the extra threads on the plugs from extending into the chamber. exposing the edges of the threads  could cause preignition.
 And that is my 2 cents.

[MRieck]

5hp in a pro stock drag car is .02 ET. That's a pretty good gain.  On my dragster the piston can hit the ground strap. I've always indexed them anyway. Takes a few minutes and can't hurt. A friend uses the washers to keep the extra threads on the plugs from extending into the chamber. exposing the edges of the threads  could cause preignition.
 And that is my 2 cents.

Did you index them with the head off? That's the only way I could see exactly what the plug was doing. I know you mark where the strap is but seeing it in the chamber is different.