Ignition performance questions & answers

Q1. I know my standard spark plug part number but how can I find a performance equivalent?

Please email us your original part number, using the contact form, we will provide a cross reference where available.

Q2. My engine has been tuned/modified, do I need a colder/hotter plug?

You should consult your engine tuner who should be able to advise you on the correct heat range to get the best from your engine. As a general rule, an engine may benefit from a colder grade of plug where modifications made have increased the temperature in the combustion chamber (increased turbo boost, nitrous oxide use, increased compression, ignition timing adjustments), a colder plug will conduct heat away from the firing tip more quickly and thus help reduce detonation/plug damage.

Q3. My vehicle has been modified to run LPG (liquified petroleum gas) or dual fuel, do I need to change my spark plugs to allow for this?

It's not usually necessary. Plugs may not last quite as long as with a standard petrol engine and the ignition system may have a harder time generating a spark. For this reason it may help to reduce the spark plug gap by 0.2mm. If spark plugs become prone to overheating, potentially resulting in damage, then it may be necessary to replace with plugs one grade colder. There are LPG specific plugs in production by both Denso and NGK, these are more expensive than standard Iridium plugs but the benefits should result in an overall cost saving due to increased service life and improved economy. Also, see Q.25.

Q4. Will I get a noticeable power increase if I replace my standard plugs with Iridium plugs?

Increases are dependant on the type and state of the current plugs, number of cylinders, cylinder capacity and a host of other details. The biggest increases seem to be from large engined vehicles with a large number of cylinders (eg 3.0L V6 and above). Having said that, any improvement on a small engined vehicle will be more noticeable. Please refer to our Iridium spark plugs page for further information. If you are currently using very old/worn or incorrect spark plugs then replacing with a new set will almost always produce a noticeable increase in performance.

Q5. Which Iridium plugs are better? NGK Iridium IX or Denso Iridium Power/Iridium Tough?

That really depends on what you want from your plugs. Denso's Iridium Tough offer the best combination of performance and service life, the downside being cost. Denso Iridium Power offer excellent performance but have a shorter service life than NGK's Iridium IX. Please consult our 'about Iridium spark plugs' page for a more detailed comparison.

Q6. How long should my spark plugs last?

That is dependant on the application and condition of the engine. High revving engines, driven hard, (eg motorcycles) will wear plugs much more quickly than a large engined car which is used for cruising. Standard copper plugs usually have an estimated service life of 10,000 to 20,000 miles depending upon design and application, Denso recommend changing their Iridium Power plugs before the maximum 30,000 miles, NGK's Iridium IX may last up to 60,000 miles in a standard use car engine. Double platinum types may last 60,000 miles or more and some NGK and Denso OEM Iridium types may last up to 120,000 miles. The plugs optimum performance level is passed a long time before these intervals so we would recommend changing plugs regularly as a matter of course, thus saving fuel costs. An engine, ignition or carburation/injection fault or poor adjustment may cause premature wear and/or failure. Tuned engines, engines driven hard, poor quality fuel amongst other factors can all dramatically reduce service life.

Q7. Can you send me a catalogue/patch/promotional item from NGK/Denso/Champion?

Generally speaking, no. We only carry catalogues for our own reference and we do not stock promotional items as a rule. Please feel free to request stickers when placing an order, if any are currently available then we will be happy to help. Otherwise, you are best advised to contact NGK/Denso/Champion directly. We are not at liberty to disclose any contact details for these companies.

Q8. Why do some spark plugs have multiple ground electrodes?

This is an attempt by the manufacturers to increase the service life of the spark plug and, in some instances, to reduce fouling. The ground electrodes can wear down rapidly in some engines. Tiny particles of metal are removed from the ground electrode each time the plug fires hence they gradually wear away. There is a misconception that a multi ground plug will produce mutiple sparks - this is not true, only the nearest electrode to the centre (i.e. the longest) will spark, as that becomes worn, another electrode will become the longest and replace it as the sparking electrode.

Q9. Do my multi ground electrode plugs outperform single ground plugs?

In most cases, no. The additional electrodes disturb the flow of gases around the spark plug tip and performance may even be reduced. In addition, for high performance applications the additional metal within the combustion chamber will retain more heat and may be more prone to detonation/pre ignition.

Q10. Can I replace my multi ground plugs with a single ground Iridium plug?

Yes, in most cases - providing a suitably sized Iridium replacement is available.

Q11. What do the different letters and numbers mean in my spark plugs part number?

Please refer to the manufacturers symbol code for NGK, Champion or Denso linked on our technical home page.

Q12. Why isn't my vehicle listed in your application guides? How can I find what plugs my vehicle should use?

Our application guides refer only to official UK or officially imported vehicles, we have very limited access to data for vehicles which were manufactured for use in other countries. We can often help identify suitable parts for 'grey imports'. If all else fails then a safe bet is to check the currently installed plugs. We can usually replace these or supply a suitable equivalent.

Q13. What should my spark plug gap be set to?

Most plugs are preset at the factory and shouldn't need to be adjusted. Please refer to your owner's handbook/manual for the correct gap setting. Our part finder application guides will also display recommended gap settings where available. Gap settings are usually specific to the vehicle rather than the spark plug.

Q14. Should I regap my Iridium spark plugs?

In most circumstances, no. The nature of Iridium spark plugs means that they are able to utilise a larger gap setting while actually requiring less voltage and straining the ignition system less. If you *have* to regap Iridium spark plugs (e.g if misfire occurs due to gap being too large) then do so with extreme care. Do not use a slide type gapping tool or put pressure on the brittle centre electrode as it may become damaged.

Q15. How do I regap my spark plugs?

To open the gap, use a pair of fine nosed pliers or a specialist gapping tool (not slide type for Iridium or other fine wire types) to carefully bend the ground electrode outwards, away from the centre electrode. Take care not to contact the porcelain insulator or the centre electrode as they can be easily damaged. Use a feeler guage to check for the correct gap size - it should be a light sliding fit. To close the gap, tap the ground electrode gently on a hard surface and then open the gap to the required setting using the method described above.

Q16. What is the correct torque setting for my engine/spark plugs?

Please refer to our torque reference page for details, noting whether you have an aluminium or iron cylinder head.

Q17. Are there any other factors which may affect which heat range plug I should use?

Yes, atmospheric conditions/altitude, grade of fuel used (lower RON (research octane number) means colder plugs are necessary to prevent detonation/pre ignition. USA has low RON fuel, Japan has high RON and UK is inbetween), driving style is also important - USA has slow roads and low speed limits meaning hotter plugs are needed, Germany has the fastest roads and sometimes no speed limit meaning cold plugs are needed, UK is inbetween USA and Germany.

Q18. Can you tell me which NGK, Champion and Denso plugs are suitable for my car?

Please use the application lookup guides on our homepage to obtain recommended NGK, Denso and Champion part numbers. There are often many plugs of varying levels of performance for a single application.

Q19. Can you supply a 'resistorless' equivalent part for use with Nitrous Oxide?

There is sometimes a resistorless equivalent to standard resistorised plugs. Our suggestion though, is to upgrade to an Iridium plug. Since the reasoning behind use of a non resistor plug is the lower voltage requirement, allowing the plug to fire under extreme combustion conditions, an Iridium plug will provide this feature as well as improving firing characteristics. Manufacturers strongly recommend using only a resistorised plug where specified due to the possibility of high tension circuit 'electrical noise' interfering with on board computerised engine management and saftey systems. Please refer to our nitrous oxide spark plugs page for further information.

Q20. What sparkplugs do I need for a Mazda RX7?

Most models use a standard plug configuration which can be found within the application guides on our homepage. The later twin turbo model uses 2xBUR9EQP and 2xBUR7EQP and it's vitally important that they are fitted the correct way around. If you are at all unsure then use BUR9EQP in all four chambers - this should not adversely affect performance although cold starting may not be as efficient.

Q21. What is the difference between the ISO and JIS standards? (BCPR and BKR or IK and IQ etc)

JIS is the 'Japanese Industry Standard' and specifies the height of the spark plug from the gasket or tapered seat of the sparkplug to the top of the terminal nut (or threaded terminal) as 53mm. ISO is the 'International Standards Organisation' standard for spark plug height and is 2.5mm shorter than the JIS standard at 50.5mm. While the small difference in height will not affect most vehicles (ISO and JIS types can often be interchanged), some vehicles (particularly with direct fire ignition or specially fitted plug caps) MUST use the correct plug standard or a bad contact between plug and cap may result. Common ISO type plugs are NGK BKR, Denso K or IK and Champion C or RC. Common JIS types are NGK BCP, Denso Q or IQ.

Q22. Why haven't you answered my enquiry?

Whilst we always try to answer genuine enquiries in a timely fashion, there are instances where this may not be the case. Email is not 100% reliable, there is no guarantee that we have received your email, please try sending again if you do not receive a reply within 48 hours. The most reliable method of contact is to use the contact form on this website.
You may have supplied an incorrect email address (common), check the settings in your email program - particularly the 'reply address' field.
There may be a problem with our/your mail delivery service.
We may have considered you were asking us for information for your own commercial gain or be in competition with us in some way.
Some requests for quotation from certain nations are ignored as they are invariably attempted fraud.

Q23. Can you cross reference Lodge CB3, Champion 9COML, 7COML?

These are long reach 18mm plugs, unfortunately we are currently not able to supply any plugs of this size. In some instances a shorter reach plug such as Champion D16 may suffice. Your best option is to try and find 'new old stock' from a vintage parts supplier.

Q24. Do you have a shop? Can I collect from you in person?

No. This has always been a mail order business, we have low overheads and low prices because we do not have a traditional shop. We do not make any provision for callers in person. If you need to buy from a traditional shop then I'm afraid we are unable to help.

Q25. Is there a plug especially designed for use with LPG (Liquid Propane Gas)?

Yes, NGK have released a range of plugs which are designed to work more efficiently and last longer for LPG applications. The plugs feature a platinum chip in the ground electrode and a fine wire Iridium centre electrode. The thread and other metal parts are plated differently to reduce the possibility of a negative reaction to LPG. Part numbers are LPG1 - LPG8, these cover a very large percentage of the UK car market. Denso also have a couple of part numbers specifically aimed and LPG fuelled vehicles.

Q26. How much does shipping cost?

Shipping is calculated by weight and destination, assuming an average spark plug weighs 50g. Some heavier spark plugs, tools, lead sets and Lambda sensors are calculated as the equivalent weight in average spark plugs - e.g. Lambda sensors are assumed to weigh the equivalent of 4 average spark plugs (200g) and each lead in a lead set is assumed to weigh the equivalent of 3 average spark plugs (150g). You can place a trial order in your shopping cart, to see shipping cost, without committing to buy.

Q27. Can I / Should I use copper grease when installing spark plugs?

No. This is extremely bad practice and we have seen plugs damaged and being reported as faulty as a direct result. There are two main issues: firstly, there is a possibility of contaminating the firing end of the plug. Secondly, and more importantly, adding lubrication will allow the plug to be tightened far more without reaching the recommended installation torque, this leads to stretching and possible damage of the threads and the risk of internal fracture, disconnection and/or reduced thermal transfer (i.e. effectively operating in a warmer heat range and possibly overheating).

Q28. The resistance value of my spark plug measured with a meter is not what I expected, why?

Whilst it is possible to measure the resistance value of some spark plugs using an Ohm meter (or multimeter set to Ohms measurement), the results may not be as expected. Being able to approximately measure the resistance value depends on the construction of the spark plug and the type of resistor used. For spark plugs which use a wire wound resistor or supressor it is usually possible to take an approximate measurement but for certain types (most notably small engine/garden equipment spark plugs), which often use a carbon pellet type resistor, measurement of resistance requires specialist equipment. An 'air gap' is often incorporated into the core of this type of spark plug for the purpose of increasing the size and precision of the spark when it arrives at the firing end of the centre electrode, effectively there is an open circuit between the top terminal connector and the firing end of the centre electrode. As you can imagine, this makes accurate measurement with a conventional meter impossible. Resistance value can only be measured by calculation using input and output current and voltage and application of Ohm's law - or using special equipment which calculates the values automatically using the same theory.