Thread: Spark Plug Part Numbers

Spark Plug Part Numbers for Boosted QR25DE's

Boosted Spec's should have a spark plug gap of .28-30ish

Two Step Colder
- Denso IKH22 $9.99


One Step Colder
- Denso IKH20 $9.99
- Denso K20HR-U11 $3.46
- Denso PKH20TT $3.26
- Denso SK20HR11 $11.95
- NGK LFR6A-11 $5.62
- NGK LFR6AIX-11 $8.48
- Autolite XP5325




If you have any additions, post them here and be sure to add if they are 1,2,3, ect colder/hotter.


Stock heat range for the QR is as follows
NGK – 5
Pulstar – 1
Denso – 16
Champion – 11, 12
Bosch - 8



Now get learned on spark plug heat range.....

Heat range

The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or racecar, it has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.

The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.

An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75–100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber.

The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite. Some manufacturers numbering systems are opposite the other, for some manufacturers (Champion, Autolite, Splitfire and Bosch), the higher the number, the hotter the plug. For othe manufacturers (NGK and Denso), the higher the number, the colder the plug.

Do not make spark plug changes at the same time as another engine modification such as injection, carburetion or timing changes as in the event of poor results, it can lead to misleading and inaccurate conclusions (an exception would be when the alternate plugs came as part of a single pre-calibrated upgrade kit). When making spark plug heat range changes, it is better to err on the side of too cold a plug. The worst thing that can happen from too cold a plug is a fouled spark plug, too hot a spark plug can cause severe engine damage

Some dyno results

I'm currently trying out the Autolite XP5325's.... they have been on for about 10 miles now (gapped to .32) without any codes (P0300, random multiple misfires)

Yes I know it will take longer than 10 miles to get that code (and yes I do have cams). However, with the NGK LFR6A-11's I just removed (had them on for about 120 miles) they kept throwing P0300 (gap .32) so we will see.....

Anyone else want to share what plugs they are running?

LFR6AIX-11 here too, stock gap at .043. Replaced my LFR5's which were awesome as well.

Your gapped at .043??? holy crap! I'm gapped at .030

Originally Posted by SlowCarGuy

Your gapped at .043??? holy crap! I'm gapped at .030

No spark blowout + better mileage and more power = winning

I wonder when spark blow out happens... meaning is there a hp range that it normally occurs.

nothing ever has to do with a "HP range". that doesn't even exist in real life engine tuning.

has to do with thermodynamics in the cylinder.

QR25DE Spark Plug Info - B15U.com - Nissan Sentra Forum

I think I have one-step colder plugs in my car right now. Im N/A and only bolted. Will this affect mpg or performance at all? Should I switch?

SRT-4 plugs work, same heat range as a stock QR

WRX STi plugs, one heat range cooler

This way you can just walk into Vato Zone/Pep Boys/Advanced etc and ask for them by application, because the brain dead kid behind the counter won't have a clue otherwise

I ran stock plugs stock gap for a few thousand miles boosted n/p but a few hundred miles after getting ngk iridium one step colder gapped 30 and my car starts feeling like its falling on its face when wot. Any ideas? Go back to stock or what?

A smaller gap will decrease power and mileage, only benefit is reducing the chance of spark blowout. If you weren't experiencing blowout with the stock gap, why go smaller?

I was stock plugs stock gap...should I go back to stock plugs stock gap or make bigger gaps in these step colder iridiums?

Colder plug, stock gap. IMO the smaller gap thing is a myth and only needed for high levels of boost or when spark blowout becomes an issue (which I have yet to see anyone complain about).

Ok is .43 stock gap on the lfra6ix-11?

.043 I believe, and yes. I didn't have to re-gap mine when I put them in.

Ok sweet ill let you know how it goes

The stock gap is 0.043" (1.1mm) and there are many reasons for that. They are mostly based on the voltage burst of the coil pack that will jump this gap and provide sufficient energy to ignite all the fuel efficiently. Flame-out can occur in highly boosted motors when there isn't sufficient burst voltage to ignite the combustion mixture. The ideal solution is to get high energy coil packs (ask cupit867) or reduce the spark plug gap. Reducing the gap, effectively produces a more powerful spark at the expense of shortening it, which in turn leads to poorer gas mileage due to more inefficient combustion.

From my experience, you should not reduce the gap unless you experience flame-out. In that case the gap should not be any lower than .035-.038". That's my honest opinion.