All about MINI A basic guide to Spark Plugs.

Ok guys, I see the same questions asked over and over about spark plug selection and fitment, so I hope this information below helps.

The first generation R50, R52, R53 petrol models were fitted from the factory with the NGK: BKR6EQUP with the EXCEPTION of the R53 JCW, this was fitted with the NGK: BKR7EQUP.

R50: NGK: BKR6EQUP tightening torque: 25-30nm (18-21.6 lbs/ft) thread diameter/pitch M14 x 1.25 socket size 16mm, electrode gap: pre-set, heat range 6

R52: NGK: BKR6EQUP tightening torque: 25-30nm (18-21.6 lbs/ft) thread diameter/pitch M14 x 1.25 socket size 16mm, electrode gap: pre-set, heat range 6

R53 Cooper S: NGK: BKR6EQUP tightening torque: 25-30nm (18-21.6 lbs/ft) thread diameter/pitch M14 x 1.25 socket size 16mm, electrode gap: pre-set, heat range 6

R53 JCW/GP: NGK: BKR7EQUP tightening torque 25-30nm (18-21.6 lbs/ft) thread diameter/pitch M14 x 1.25 socket size 16mm, electrode gap: pre-set, heat range 7

All the above mentioned NGK spark plugs have a Platinum ring around the electrode tip, NGK also provide the following with an Iridium electrode tip, however be careful as the following have a tip projection of 1mm extra in length over the above!

BKR6EIX Iridium tip, this is an alternative replacement for the BKR6EQUP with the same heat range (6)

BKR7EIX Iridium tip, heat range (7) this is 1 heat range colder than the BKR6EIX

BKR8EIX Iridium tip, heat range (8) this is 1 heat range colder than the BKR7EIX

The second generation R55, R56, R57 petrol models are fitted from the factory with the BERU: 12ZR6SP03 with the EXCEPTION of the Cooper S, these are fitted with NGK: PLZBR7A-G, and the JCW are fitted with the NGK: ILZKBR7A-8G

R55: One/Cooper: BERU: 12ZR6SP03 tightening torque: 20nm (14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm electrode gap 1.0mm, heat range 6

Cooper S: NGK: PLZBR7A-G and JCW: NGK: ILZKBR7A-8G tightening torque: 15-20nm (10.8-14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm, electrode gap: pre-set, heat range 7

R56: One/Cooper: BERU: 12ZR6SP03 tightening torque: 20nm (14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm electrode gap 1.0mm, heat range 6

Cooper S: NGK: PLZBR7A-G and JCW: NGK: ILZKBR7A-8G tightening torque: 15-20nm (10.8-14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm, electrode gap: pre-set, heat range 7

R57: One/Cooper: BERU: 12ZR6SP03 tightening torque: 20nm (14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm electrode gap 1.0mm, heat range 6

Cooper S: NGK: PLZBR7A-G and JCW: NGK: ILZKBR7A-8G tightening torque: 15-20nm (10.8-14.5 lbs/ft) thread diameter/pitch M12 x 1.25 socket size 14mm, electrode gap: pre-set, heat range 7

So with this basic information above out of the way, let's move along a little to what I have seen posted quite a few times.

Q1: What's the best spark plug for my Mini ?
Q2: Can I put Cooper S or JCW spark plugs in my One or Cooper ?
Q3: and JCW spark plugs in my S ?
Q4: and will I get any power performance gain in doing so ?

As you may have guessed, the answers to the above questions are not straight forward. Very basically, the answers to questions Q2 / Q3 are YES, with a caution in understanding the effects a colder heat range spark plug may have when fit into a stock engine!
Question 4: is although the Iridium is seen to be the performance spark plug, the fitting of the Iridium spark plug itself will not give any power performance gain. Many people report that when they changed from Platinum to Iridium, they felt a livelier throttle response, when in fact what you will have done is simply renew old tired spark plugs with fresh new spark plugs. The ignition system now performing as it should do, thanks to the change of tired old, for new fresh. The material change in the case of Platinum to Iridium has played no difference! The other question (Q1) will be answered as you read on.

Platinum and Iridium are used for their hardness and resistance to wear. This gives longevity between service intervals, with Iridium being the harder of the two. Iridium is 6x harder and 8x stronger than Platinum. Iridium has a very high heat melting point of 2,443 degree C. With all these factors taken into consideration, Iridium is generally thought of as being the best material for the electrode tip resulting in a fine wire spark plug. Well, in terms of less maintenance/extended service intervals, yes it is, however Iridium is a very very dense material and is a very poor thermal and electrical conductor (see chart below).




Some of you may well be asking "Why use it at all if what we see/read here is true?" As touched upon earlier, Platinum and Iridium are used for their ability to provide longevity between service intervals and the resistance to wear, especially Iridium. That's it.

Now that you have seen the thermal and conductivity chart, we can see that Silver is the best of all metals when it comes to thermal and electrical conductivity, so why not fit these instead of the more popular Platinum and Iridium? Very simply, you would need a more regular maintenance schedule, unlike the Platinum and Iridium spark plugs, which can be fit and forgotten about for 20,000 miles +. If you use or consider using Silver or Copper spark plugs, remember these will require more frequent service schedule replacements than the Platinum or Iridium. If you are looking for more performance over longevity, or you track your Mini, then you should be aware and looking if not using other alternatives to Platinum or Iridium.

Now I've got you wondering "So what's the best spark plug for my Mini?" That all depends on what you do with your Mini, and of course your budget. If your Mini is your daily driver and you rely and trust your dealer (they know best!) then you may as well stop reading now. If on the other hand your Mini is your daily driver come weekend warrior, or is just your weekend warrior, and you do your maintenance yourself then read on.

So you're now thinking about the possibility of a better performing spark plug. With the Mini you must run a Resistor spark plug, if you were to run a non-Resistor spark plug you will have issues with the electronic steering system and the electronic throttle (drive by wire system). So lets now forget about stock/standard Platinum and Iridium spark plugs, and concentrate on PERFORMANCE. If you want the best performance then you have to look at Silver or Copper. As you can clearly see from the thermal and electrical conductivity chart, these two materials are No 1 Silver and 2nd Copper, so you've upgraded your engine/fuel system/ignition system (wires and coil or coil overs in the case of those running gen 2 or converted your gen 1 to coil overs) and had your Mini tuned; why are you still running Platinum or Iridium spark plugs? The noticeable difference can be quite significant when running Silver or Copper spark plugs. Just because these tend to be aimed at and marketed as Performance/Racing spark plugs does not mean their sole purpose is for track use. However, the term "Racing spark plugs" is generally just an indicator of the colder heat ranges available from the standard stock spark plug specified for your particular Mini.

The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine cylinder head, it has been found the optimum combustion chamber temperature for petrol engines is between 500 degrees C – 850 degrees C. Within this range it is cool enough to avoid pre-ignition and plug tip overheating which can cause engine damage, while still being hot enough to burn off combustion deposits which cause fouling.

The spark plug can help maintain the optimum combustion chamber temperature. 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 cylinder head which, in turn, 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 racing 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 degrees C to 100 degrees C from the combustion chamber!

The heat range numbers convention used by spark plug manufacturers are generally the higher the number, the colder the plug.

Do not make spark plug changes at the same time as another engine modification such as different injectors/timing changes different boost loadings from your chosen forced induction, as in the event of poor results it can lead to misleading and inaccurate conclusions about the cause. 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, while a too hot spark plug can cause severe engine damage!

This next little bit of information may not be of much use to many of you reading this, however those that have the time and patience may want to try degree orientation (indexing). This is lining up the ground electrode with the inlet valve/s. This usually has a window of 45 degrees, working from the direct central position alignment of the ground electrode with the inlet valve/s. Getting this correct can be quite difficult. Firstly you will need to mark the ground electrode position onto the spark plug hex head or porcelain body with a suitable marker. Then unscrew the sealing gasket from the spark plug. You then need to place a flat Copper washer of a specific thickness of your choice directly onto the spark plug shoulder and then screw the sealing gasket back onto the spark plug. Once you then install and correctly torque down your spark plug you will get an indication as to the general direction of the ground electrode in relation to your inlet valve/s. You may need to do this many times using + or - to your first installed washer thickness to get the ground electrode in the correct orientation to the inlet valve/s, this operation can give a small benefit in terms of performance, but generally this gain can only normally be read on the dyno or felt at the track, and such is the small gain it may not be worth your inconvenience, time or effort. However that said, if you are looking for every possible FREE amount of performance gain, then it may well be worth your while!

Now all of the above information is just a very quick guide to spark plugs. There is a lot more I could and can add, however I hope it will help all who read this to understand a little more about spark plug selection and fitment for the Mini.