Spark Plugs

[Trex101]

From what I've reseached so far the standard gap for copper is .8 and Iridium/Platinum is 1.1 some have shortened the gap to .8 in the I/P plugs due to high boost (20+psi) due to the spark being blown out by that much boost and the shorter gap fixed the problem, so it speaks for itself.

<{POST_SNAPBACK}>

For normal boost it's recommended to use 1.1mm gap, be it copper, platinum or iridium plugs. It's when you increase boost or HP you must reduce the gap (about 0.1016mm for every 50 hp you add).

NGK FAQ

Edited February 7, 2006 by Trex101

[Craved]

with old coil packs and running 18 psi, i had to go down to 0.6 with some "6" range coppers .. still blowing out up the top though... just under 300rwkw

new coils have arrived, hoping to run back to around 0.8 if possible..

Edited February 7, 2006 by Craved

[R33S2]

Thanks for that Trex101 but now I'm totally confused as alot of members here have stated that they gap theirs at .8, unless they are all running high boost.

[Sydneykid]

This is not a simple discussion, the subject of spark plugs is quite complex. Following are some Skyline/Stagea specific clarifications based on my experiences;

Copper is a better conductor of electricity than iridium or platinum, so a copper plug can run a larger gap than an iridium or platinum plug. Iridium and platinum plugs are used for their life, they last longer, NOT for their performance. This is because of the increased service intervals and the high labour costs involved in changing plugs. The total cost over, say, 100,000 k’s is cheaper using iridium or platinum plugs than it is using copper plugs. That’s the case if you pay someone to change your plugs, if you change them yourself, then copper plugs are cheaper.

The numbers;

Copper plugs last for 8,000k’s and cost $18 for the 6

Iridium or platinum plugs last for 40,000 k’s and cost $120 for the 6

$18 X 5 is less than $120 X 1 = copper plugs are cheaper

But if the workshop charges you say $40 a time to change the 6 plugs = iridium/platinum plugs are cheaper.

Spark plugs come in a variety of gaps, for example NGK BCPR6ES come in 1.1 mm gap (BCPR6ES – 11) and in 0.8 mm gap (BCPR6ES – 8). Retail outlets carry the most popular part number (in this case BCPR6ES – 11). It may be that some popular N/A car uses the same plug configuration, so they carry that plug gap. It is NOT because that plug gap is somehow “standard” for that plug configuration.

As we increase boost (from standard) the inlet airflow and combustion pressure can literally blow out the spark. To overcome that we can either use higher output coils to give a “bigger” spark that will jump the gap even under the higher pressures. Or we can reduce the gap that the spark has to jump. Up to a point, reducing the gap has no real bad effects, but if we have to reduce the gap too far the engine will loose power. This is because there is simply not enough spark to properly ignite the fuel. An experienced dyno operator can pick this because he has to advance the ignition to hold the power. Advancing the ignition gives more time for the smaller spark to spread the flame. This is obviously a band aid, as we start to run into detonation problems if we advance the ignition too far.

My suggestion is (if you change your own) use copper plugs of the correct heat range and gap. If you can’t get the right gap spark plugs off the shelf, then gap them down.

Simple rule of thumb for DIY plug changers;

Standard boost = BCPR6ES – 11

12 psi = BCPR6ES – 8

Up to 19 psi = BCPR7ES – 8

Over 19 psi = BCPR7ES – 6

Until we get so much airflow that the standard coils won’t fire the 0.6 mm plug gap. Or the power drops off.

Then its time to upgrade the coil packs, go to CDI or whatever. We can usually increase the plug gap and start the process all over again.

Warning, this is not a definitive explanation, the result is a simple rule of thumb that you can employ. Then you can fine tune the slection for you own specific purposes and remember every engine is different.

cheers

[PHaT MR30]

May sound dumb, but why do you change the heat range of the plug above 12psi?

[Trex101]

Copper is a better conductor of electricity than iridium or platinum, so a copper plug can run a larger gap than an iridium or platinum plug.  Iridium and platinum plugs are used for their life, they last longer, NOT for their performance. 

cheers

<{POST_SNAPBACK}>

It's true that copper are better conductor of electricity but copper is soft and doesn't less more than 10k. The new Denso/NGK Plat or iridium plug which feature fine wire technology (0.4-0.6mm center electrode) will provide much lower voltage then copper to jump the gap thus less misfire.

One disadvantage is the lower lifespan of 40k compare to 100k for normal plat or iridium plugs.

[Sydneykid]

May sound dumb, but why do you change the heat range of the plug above 12psi?

<{POST_SNAPBACK}>

My experience has been that you tend to get a bit of detonation reduction by lowering the heat range. This becomes more important as boost rises, I picked 12psi as the rule of thumb as that is when the standard turbo is usually upgraded. So it's a good time to go for a lower heat range plug.

1. It's true that copper are better conductor of electricity but copper is soft and doesn't less more than 10k.

2. The new Denso/NGK Plat or iridium plug which feature fine wire technology (0.4-0.6mm center electrode) will provide much lower voltage then copper to jump the gap thus less misfire.

3. One disadvantage is the lower lifespan of 40k compare to 100k for normal plat or iridium plugs.

Suggestion follow;

1. That's why I used 8,000 k's in my example.

2. True, but (there is always a but) the copper core still conducts better. All they are doing is trying to get back what they lost by going to iridium/platinum. They can't improve the conductivity, so they reduce the anode surface area to concentrate the spark. Some people argue that this reduces the size of the spark and therefore slows down the flame propagation.

3. Quite logical, since the anode is smaller, it wears out quicker. I have yet to find a car that doesn't get improved performance when the iridium/platinum plugs are changed at 40,000k's. This is despite the manufacturers claim of 100,000k's, they might "last" 100,000k's but the performance drops off noticeably over 40,000k's.

What I was aiming for with the original post was to give people an easy to understand and quick to implement rule of thumb. Not the definitive encyclopaedia of spark plugs.

cheers

[FATGTS-R]

Another question SK.

What would be the negative side effect of using the "7" heat range plug on standard boost vehicle?

[PHATR32]

does using a colder plug on standard boost etc cause the plug to foul??

[sidewazegtst]

Hey guys.

Ok just wanted to be sure on a couple things.

I gave the part number BCPR6ES to my Father N Law (who's a sales rep for an automotive company here in Canada) and "apparently" NGK has changed there numbers here and are now BCPR6E. They've dropped the "S" but when I punch in both numbers on www.ngk.com both types of plugs come up so I'm a little confused.

The ones I have are NGK V-Power RESISTOR TYPE plugs, #BCPR6E and I just want to know I'm all good to use these? I'm also running stock boost for now so according to what's been said I use a 1.1mm gap right?

Thanks for this fella's, I just want to know I have everything right so I can change my plugs tomorrow.

BTW, this thread REALLY must be a "Sticky" as it's full of great and usefull info that people can refer to whenever needed.

[R33S2]

Thanks Sydneykid I'm glad we have a guide to gaps now (not a bible) but experience beats textbooks.

And thanks again to all who helped.

[R33S2]

I finally got around to taking them out.

Shape and form are unchanged and gaps were spot on @ 0.8. after 30k

The reddish colouring is not covered in the NGK FAQ anyone have a suggestion why these are reddish? Is it the I only run BP Ultimate?

The slightly darker NO.6 is an area for concern?

[Trex101]

I finally got around to taking them out.

Shape and form are unchanged and gaps were spot on @ 0.8. after 30k

The reddish colouring is not covered in the NGK FAQ anyone have a suggestion why these are reddish? Is it the I only run BP Optimax?

The slightly darker NO.6 is an area for concern?

The Reddish colour are usually due to additives in fuel. Did you use any fuel injector cleaner during the time your plugs in there?

For the foul no.6 plugs, it's normally due to carbon buildup on the no.6 valve or injector clog, since the rest of the plugs look ok.

IMO, the cheaper way you can do is to use a strong dose of injector cleaner like Redline SI-1(one bottle for the 1st tank, than lower dose on the 2nd tank). If that doesn't help then you got to sent the injector for ultrasound cleaning.

[R33S2]

Thanks Trex101 will do an injector clean too.

Car is running great now, when I took it apart, for the plugs, alot of everything was loose, and with a light brass brushing I noticed a slight scale came off the plugs too.

Put the boost backup after some careful testing and holds fined through to redline cut.

[Dizmo]

What is the diameter of the threaded section of a spark plug that fits in a RB20DET engine?

Edited March 29, 2006 by Dizmo

[Busky2k]

I've used BKR7E or BCPR7EY (Copper V-Powers) and they have never have missed a beat. Lucky for me I have an SR20 so changing the sparkies are a 5 minute job.

Absolutely no fouling problems with a 7 heat range on a street vehicle.

[The Mafia]

well, the brk7e's made very little difference in my r33 SII with GT30 hanging off the side running 16psi of boost.

I think I might change to 8's

Can anyone say if this is a bad idea or not?

[Trex101]

If you tighten the plug tooo much they can be a real @#$%^& to get out.

The more feedback the better, just to confirm I am on the right track.

One trick i learn from old timer, coat a layer of grease to the plugs thread before installation. Set 30% lower torque to the plugs and you are good to go. It will never seize.

[DEVL25]

I'm running Splitfires in my RB25, also running 12psi.

Should I have the plugs gapped at 1.1 or 0.8?

[ross80]

ive just finished replacing my plugs with bosch fr8 dcx with a 1.1 gap.

The car is detonating all over the shop. runs really smooth under boost. But if you put foot in, it just starts going put put put and hesiitating.

weird as it runs really smooth apart from that.

Help?! I am over this car!