Indexing spark plugs

[Bigvolvo]

Seen a few comments recently about indexing spark plugs. As far as I understand it this means orientation of the plugs so that the open side of the plug gap faces the inlet valve. Firstly, why not use surface discharge plugs which would solve this issue; if there is one. Secondly, is not the actual position of the electrode far more relevant to efficient combustion than its orientation. So does indexing really achieve anything?

[Big Jim]

I have searched for a definitive answer , there does not seem to be one . As it is free to do I have done it . I am not convinced it makes any difference

[Lotus-e-Clan]

How are you measuring "the lack of any difference?

Power?
Torque?
Throttle response?
Economy?
Service intervals?
Carbon Distribution?
Ignition timing limits?
Octane tolerance?
General Refinement?

..and over what period of time are you doing those measurements?

Just as easy to dismiss a concept without data as it is to believe in the concept.

For me it's about "Marginal Gains" it all adds up in the long term. In the case of the Clan's engine (which is my project car and gets the most development) my yardstick is reading carbon distribution on plugs and within combustion chambers. The aim being same pattern for all cylinders and minimising carbon build-up. For any given combustion chamber design you need to try 4 plugs in 4 different positions for a while and then decide on orientation. Use a borescope to view effects within the chamber and also read plugs.

Some of the listed measurements are bound to disappoint - like gross power and torque - because the normal mode of measurement eg "dyno" has poor resolution (smallest measurable difference) in terms of longer term marginal gains. With marginal gains it's about the collective effect - any single adjustment is bound to disappoint when measured on it's own.

EDIT: A bit like fitting alloy wheel nuts then finding no difference at the weigh bridge ... but you could alter damper settings to take advantage of the reduction in unsprung weight!

Or reducing pedal weight by a few grams on a racing bike and then measuring climbing or flat out speed only to find no discernible difference .. but after 120 miles in the saddle you arrive less fatigued and win the sprint!

[madmax]

As well as my Lotus cars I also run a First Generation Honda Insight as something to cover many reliable and cheap miles in. These things are so good, I've now had three of them and on a trip from Cambridge to home the other day I averaged 95.1 mpg!!

It's the closest you can get to fresh air motoring

The reason for this post is to chip in with my Honda experience as the Insight actually also has Indexed spark plugs. Each of the cylinders (three of them) is marked with an A, B, C or D and when plugs are ordered from Honda, they ask for these details.

Allegedly, on such a tiny engine where the collective result of all their technologies go a long way to making it THE worlds most economical car with the lowest CO2 emissions, this indexing is apparently quite important.

Soemthing else Honda did is keep weight to an absolute minimum - we've heard that before somewhere..........................

[Bigvolvo]

After reading up about this I suspect that it very much depends on the shape of the combustion chamber. Indexing spark plugs and cutting the earth electrode about goes back a long way. I think it may stem from the days of side valve engines and the wedge shape and position of the spark plug. Back then, with poor electrical systems and ineffective intake manifolds it may have had led to substantial improvements. I can also appreciate it being worthwhile in a set up as lean as that of the Prius. For many cars though I think the results are likely to be very small.
currently I use NGK bpr6es, Ive found them less prone to oiling than 7s. Id like to go surface discharge next time.

[fueltheburn]

The LC engine should be using the 6s and the HC should be using the 7s.
The projected nose design of the plug is designed to get the spark deep into the combustion chamber - a surface discharge typically doesn't have the same projection... just an opinion but I think in this case the ignition of the mixture may not be as strong as a result of using the surface discharge. It will be interesting to see your results.

I have tried the bosch super 4s, standard plugs and iridiums in the Excel. Iridiums are what I will always use now.

Super 4s are good at idle and starting but higher up the rev range become weak due to the spark choosing the shortest gap and not having a big enough kernel to properly ignite the mixture.
Standard plugs - never had a problem.
Nology silver plugs - very good but too costly for too little gain. Used once in a turbo charged astra.
Iridiums - stronger spark, for me I noticed an improvement over standard and these now set the standard for me and wont go back.

Any improvement on an engine no matter how small is a gain in efficiency as Tesco remind you "every little helps"
I personally consider the extra half hour it takes to roughly index all the plugs towards the inlet a worthwhile effort.
My un-burnt hydrocarbons on a gas analyser went down when using iridiums and indexing the plugs.