Its time to change the spark plugs in the rallycar and was wondering what other plugs people are using in their motors. I've heard that Iridiums are good, i'm also interested in what plug gaps people are using, does it make a difference?

I have also a problem, especially having a race car where the stop-starts of moving the car around and long intervals of not running the cars engine at lengthy periods fouls the plugs....
Once they are fouled the plugs are stuffed and need to be renewed. This happens every 6 or so starts then the plugs need changing unless I run it for a long period. I cant even clean them with emery paper to clean them up...they have to be changed. Got any ideas?

Lemonhead
I have a set of NGK Iridium plugs that i plan to use in my coupe. They are BPR6EIX, but a colder heat range may be better suited to competition use.
I have used the NGK Platinum plugs for years & I swore by them, but the platinum plugs are no longer available. The Iridiums are the replacement, & are better.

With the Nissan High Energy ignition that i will be running, you run 44 thou [1.1mm] gaps, but with the Iridium plugs, you need less voltage to fire a spark across a given gap at a given compression pressure, so i will be experimenting with gaps out to as much as 50 thou [1.25mm]
The bigger the spark, the more sure the firing of the charge, & the more complete the combustion, particularly if one is running a leaner mixture when cruising, but then, race cars don't do that a lot, do they.

Now for the bad part. At full retail, you won't get a lot of change from $100 Au for a set of four. On the upside, you can expect a service life that will outlast a lot of newly built engines that are used in some of our members cars.
I paid $88 for mine & i believe that they are a bargain.

Agreed. Platinum plugs really don't work better, but they wear more slowly. That is, a new set of plugs (any brand) will work fine ... but the platinum are still working fine after many months while the regular ones need to be cleaned and gapped every 12 months on a well-tuned carbureted engine.

The gap can make a huge difference. Even with a stock A12 and stock ignition, changing gap from .030 to .035 can make a noticeable difference. As Dman says, larger gap is better -- provided a high-enery ignition system can fire them.

Converted, are you talking about fuel-fouling? I hear it is common on race cars running terribly rich, especially without any choke. The real solution is to control the air/fuel mixture. Which is why plugs in EFI cars go 100,000 miles without cleaning (160,000 km).

yes it is fuel fouling...yes it does run rich and with no choke, so what i may be hearing is put up with it or run EFI

Can anyone tell me the recomended gap size for a CA18DE, As im putting new plugs in at the moment. And ive alredy done a search.

The gap depends on the igntion system. Which one do you have? If it's a stock system, what year and what car model did the CA18 come out of?

Most of the '80s high-energy stock systems use 0.044 to 0.053 inch gap. I would say you can't go wrong with using 0.044, if you cannot find the exact spec for your system.

All i know about the engine is its S13 and eng# 240964W if that helps you identify what year. I guess it would be 89 to 90 model

Quote: Actually, they do work better, as well as wear much longer.
With a much finer center electrode, they need less voltage to fire a spark across a given gap at a given compression pressure. This means that you can run a wider gap at the same voltage requirement as before.
Alternately, if the ignition was breaking down at a certain rpm level, it should run better at the same rpm if Platinum or Iridium plugs are used with the same gap, due to the lower voltage requirement.

How much lower? I don't know, but, as i wrote earlier, i will be experimenting with gaps to try & find the widest "practical" gap that i can use long term in a street engine.
My 9.something to 1 compression should allow a reasonable scope here.

This is something I am also interested in.
Given the following information can anyone give me some advice? :

I have recently installed a Pertronix Ignitor in the place of my points breaker systems.
I am using the stock coil still.
On the advertizement they say it provides better power to the spark plugs.
Can I install the plugs you guys are talking about that will provide better spark?
Or must I keep using the standard spark plugs that is in the workshop manual.
What about the gap?
The standard gap that I am currently using is 0.8mm.
Why I am asking is I am after even better fuel economy.
Anything that can improve it I want to try.

Can you believe it.
I once wanted to do performance improvements to my A12 now I want to do economy improvements.

Many thanks.