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Wednesday, May 05, 2010

RB26DETT , RB26 Spark Plugs, VR38DETT Spark Plug

Stock Spark Plug for an RB26DETT

* P = Premium platinum
* F = 14, 19mm(3/4") reach, 16mm (5/8") hex
* R = Resistor
* 6 = Heat range 6
* A = Firing end construction
* -11 = 1.1mm gap (0.044")
Heat range for NGK plugs 2 HOT - 11 Cold

A good stock replacement spark plug for an RB26 is a BCPR7EIX. Its an NGK Iridium plug. Heat range is 7 which is one heat range cooler than stock. Its readily available in the US. I would use them up to about 500 horsepower on an RB26. Above that I would look at an 8 for a street car, cooler if its a track car.  I have had good luck with NGK plugs, I insist on them, on the race cars I work on. One less thing I ever have to worry about.

Spark plug gap. The "gap" is the distance between the ground electrode and center electrode. The further the two are apart, the more potential (voltage) that is required to arc, or jump that gap. Some people run a super tight gap, because of misfire issues. If the car is pretty stock, then it should have no issue arcing or firing across 1.1 mm or 0.044 inch. At bigger power you might go down to 0.8 mm or 0.031 inch. Generally a bigger arc is going to give you a more complete burn in the combustion chamber. 

This is from NGK on spark plug gap.

"Although the NGK factory will set the gap to a preselected setting, this may not be the right gap for your particular engine. The incorrect plug gap for your engine can contribute to a high rate of misfires, loss of power, plug fouling, poor fuel economy and accelerated plug wear. It is always best to check the gap against the manufacturer's specifications. If adjusting the gap on fine wire or precious metal plugs such as platinum or iridium, be very careful not to apply any pressure or prying force to the fine wire center electrode or insulator as they can be damaged. The gap should be adjusted by only moving the ground electrode. 

Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005"."

Lots of guys like to run the cheap copper plugs. I never had much luck with them. Electricity takes the path of least resistance.  You can see one owners fix for leaking spark, that was causing misfires on his Nissan Skyline GT-R. Watch the video if you have an RB26. Sometimes just a little work/cleanup is required to fix an issue, rather than just parts replacement. However a lot of people would just rather replace a part than fix something they already have. Too many people get new "aftermarket" coils, which may fix the issue, but really don't address the issue. The combustion chamber is a very harsh environment. Lots of heat, lots of pressure. Heat = resistance. High resistance means the spark will not arc across the spark plug gap.  This is why I like the Iridium plugs. Fine wire on the center electrode makes it easier for the arc to jump. The really expensive, and good plugs, are double fine wire.

A lot of people also run the "K" or ISO length plugs. These are 2.5 mm shorter than the JIS plugs.  If you are trying to get the most out of your ignition system, don't short anything.

JIS length - 53 mm from seat to plug tip. STD GT-R plugs are JIS length.

ISO length - 50.5 mm from seat to plug tip

Racing NGK plugs. Recommended by Nismo

Double fine wire Iridium plug. If you are serious, run these. 
* R7238-7, 8,9,10.
o Replaced by R7436-7,8,9,10
+ Hand made fine wire racing plug
+ 14mm, 3/4 reach, 5/8 hex, JIS length , fine wire iridium center electrode
R7436-10 part number 4900 $ 38.81 each JIS - I like
R7116-10 part number 3179 $22.34 each ISO - I have used
R7119-10 $33.12 each ISO - Not used - should work
BKR8EIX $7.60 each ISO - Not used - should work
IFR8H-11 $11.71 each ISO - Not used - should work
NGK Racing plug 4898 R7436-8 $41.52
NGK Racing plug 4899 R7436-9 $41.52
NGK Racing plug 4900 R7436-10 $41.52

NGK IRI (WAY)(TOP)(MAC) plugs have a 0.6mm iridium tipped Center Electrode with a tapered cut ground and are sold under the name Iriway, Iritop and Irimac throughout Japan and other select countries.  In the US and Europe these same plugs have been released under the IX Iridium Series and can be identified by their alphanumeric part numbers. The list below shows appropriate interchanges.  The IRI Series and IX Series are produced in the same NGK factory.  They are identical in construction, with packaging and marketing being the only difference.
IRI Series=Alphanumeric Part#
(Not available in the US.  Can use BKR8EIX, which is identical but is ISO length instead of JIS)
(Not available in the US.  Can use BKR9EIX, which is identical but is ISO length instead of JIS)

Stock R35 GT-R Spark Plug


R35 GT-R Spark Plug. DILKAR8A8


Anonymous said...

Hello Sean!
If the sparkplug threads are all wet with oil what does it mean on an RB26? Tips are dry, no bluish smoke on exhaust. Was puzzled to find the threads are wet.

Sean Morris said...

Wet threads on all them? Maybe just some oil sneaking by. Maybe when adding oil. Maybe old stuff stuck in the threads from last time. Not much to be concerned with honestly. Monitor. See if anything changes.

Anonymous said...

Yes sir. All of the threads has dark brown oil in them, as well as the sparkplug washers. At first I thought it's fuel, but it doesn't smell like one. As for the tip they're dry. But on the base of the J hook tip it's black but not really wet though, but was thinking the oil has got there also. Do the RB26 has sparkplug oil seals in them just like the others? Was reviewing the gaskets I had before but I don't recall circle oil seals for sparkplugs. But I see 3 big alllen bolts beside the plug holes, was thinking it needs retightening. ��
Also heard some owners and tuners hate iridiums. Is heat range 6 ok in a street seldom used Gtr that is around 390hp or you would already recommend 7? Because some say 7 fouls earlier especially if the car isn't used a lot.

Sean Morris said...

I wouldn't put too much into it. Clean and monitor. 7 are fine for a seldom used car. I actually run -10's and they need a good run to clean them off every now and then. I like iridium, as they are easier to fire than other plugs. The electrode can be thinner.

Anonymous said...

Yeah was also thinking of blowby oils or going out turbo seals. Also thinking of oil catch cans coz I know the RB26 move oils around on the system right?
Thanks for the tip. Guess I'll be going cold plug 7 iridiums next year.

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