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MG MGB Technical - Plug Indexing

Has anyone tried spark plug indexing on their B, did you find it made an improvement and if so where did you get the washers to index your plugs?
Joe Dufresne

What sort of improvement do you expect to see? I doubt there would be any noticeable improvement in power or fuel consumption. If there were you'd probably need some rigorous scientific tests to prove it since the difference is likely to be small!

For those who don't know indexing plugs is where you make sure the position of the spark plug electrodes is 'correct' in the combustion chamber. I think the idea is that the ground electrode doesn't block the spark from the incoming charge (I am not 100% sure on the details)?

Simon Jansen

I tried a Halo Plug about 3yrs ago. I remember when I put them in the idle went up by about 300 rpm. It was noticable enough that I had to reset the idle srews. The very nature of these plugs is that they are self indexing. FWIW they have my recommendation.

www.lsgbrisk.com/
Ed Madak

Joe ,
YES I have done it.
NO there was no detectable ( on a rolling road dyno with a standard tune engine ) benefit.
As an aside I think the benefit would be there the more highly tuned the engine is. In F1 engine there is probably some advantage but on a street engine it is doubtful. On the other had , it costs nothing and there is the same to loose so try it and see what happens on your car.

WASHERS? Didn't use them. I marked a line on the plug shell with a marker pen in line with the electrode and then installed the plug noting where the line ended up.
Remove the plugs and rotate to adjust for the line and reinstall and torque to spec.

Pete.
Peter Thomas

FWIW, I do index my plugs...it's easy enough, since any 4 plugs will generally get pretty close, although there is also some variation in torque value invovled.

Can't say I've noticed (nor would I expect) much difference, but it doesn't hurt, and there's some theory behind it.

Curtis Walker

Ok, I'll admit it is one of those things that can't hurt but what are you guys indexing them to and why? I mean what is your reasoning behind how you indexed them?
Simon Jansen

As was said up front, the 'open' side of the electrode should face the majority of the combustion chamber so the flame front doesn't have to go round corners. It's a bit like a dog licking its privates - pointless but harmless and if it keeps them happy ... :o)
Paul Hunt

I index my plugs.

I use a felt marker to indicate opposite (180º across) to where the hanging electrode is - and then I position the mark to face the intake valve.

Positioning the spark plug in this manner assures that the hanging electrode is not in the path of the incoming gases.

This way, the incoming charge of fresh gases is given a better chance (albiet a small one) to blow clear some of the exhaust
combustion debris on the electrodes.

It won't give you much of a boost in horsepower, but it's supposed to lessen the possibility of coughs and misfires.

Either way, it's chicken soup - it can't hurt.
Daniel Wong

Way back in the middle-to-late sixties, when piston domes were outrageously high and "scientifically" shaped, you needed to index plugs to prevent the piston from hitting the electrode.

Today's thinking is to keep the gap pointed away from the cylinder wall so the flame front travels into the center of the cylinder/combustion chamber. Also, the ground electrode is cooled somewhat by the incoming fuel-air mixture.

YMMV.

Wayne
Wayne Pearson

I agree with Wayne,

The idea is to leave it open to the chamber.

Sean
Sean Brown

Actually Wayne - this is one of those rare areas where your mileage probably won't vary! :)
Curtis Walker

So then that would be "YMPWV"!!

Take that netlingo-ists!

Wayne
Wayne Pearson

This thread was discussed between 14/10/2009 and 16/10/2009

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