Indexing Plugs On The Rb26dett

[rev210]

Just a question for anyone who has got a winning formula for the indexing of the plugs on an Rb26dett to give their feedback.

For those who don't know what indexing plugs is, it's basically lining the plugs grounding strap in a particular direction that achieves optimum spark characteristics under load. The 'gap' where the spark occurs has a directional charateristic and in most engines there is power and more reliable spark under load to be had by getting this direction right.

You are able to adjust the postion of plugs by using wafer thin washers to achieve the right factory tension while getting the direction you want.

[Sydneykid]

Indexing plugs, wow that's an old trick that I haven't used for ages.

I don't even think I can remember all of the theory for a turbo engine. Is it to point the earth electrode at the inlet stream so that the spark doesn't blow out as easily? Plus that woud delay combustion a poofteenth, so might be good if you have preignition problems.

On an N/A engine (Chevy) I remember we used to point the electrode away from the quench/squish. So that the spark is NOT shielded, to give a quicker more spread ignition. That would be hard to do on a RB though.

If I also remember rightly the claim by the indexing washers makers was a 5% improvement at best, that's both in power and economy.

It used to be such a pain (in the back) to do on a V8, took about an hour to do all 8 plugs. The RB would only be 75% as painful, plus the plugs are a lot easier to get to.

Let me know what sort of result you get, I am sure Moroso or Jacobs still sell the indexing washers. But the plug size might be a problem.

cheers

[rev210]

Hi Sydneykid,

I was chatting with RIPS a while back about nitrous and we got onto the plugs setup and at the time he wasn't ready to give his indexing secret up.

In the instances I have done this it has always been of benifit.

If there isn't any one out there with data perhaps we can start with people visiting the dyno who would like the chance of maybe upto 5% more power?

The chev example sounds right but, not knowing where/which way the squish/quench is when looking down at the bolted down head is my handicap at this stage. If I had the head off it might give me something to go by.

[WantGTR]

Digging up an old thread. Don't know how I came across this but it sounds interesting. Has anyone tried it out on an rb? Which is the optimum way for the earth strap to face?

[GTR_JOEY]

Here I was reading the thread thinking SydneyKid had made an sau comeback..

9 year old thread

[GTSBoy]

I think there is little value in indexing plugs on 4 valve engines. Certainly worth it (for the last 0.25%) in 2 valve engines. Benefit would be smaller on 4 valvers. That said, at the very least it would be preferable if they all faced broadly towards the inlet side or broadly towards the exhaust side*, rather than being randomly distributed.

* or even all towards the sides of the chambers I suppose.

I did it on my ALFA. Once. Cost me an extra half dozen plugs and an hour and I benefited approximately bugger all.

[White GTS-T]

Copied from NGK's website.

"This is for racers only !!

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".

[Blackkers]

well put. 1% of power can be had with just a poofteenth extra boost

[XRATED]

when your at the end of the road with everything else, there are gains to be had under particular circumstances with a highly strung rb.... more than 1%. Just costs time and money to find out what works for your combo... most people don't want to spend the time or money to find out.

J.

[GTRPSI]

Usually the gap faces the intake, ground strap between the 2 exhaust valves when indexing plugs on quad valve heads.

Im surprised nobody metioned sidegapping the plugs yet.