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FAQ: Spark plugs


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The Spark Plug FAQ


Q. Why would I need to use a different Spark Plug from the standard Denso PK16R11 in the NA or the PK20R11 in the TT?

A. If your Supra is still standard then there is no need to use anything other than the stock recommended plugs from Denso, however if these are hard to come by then you best alternative is the NGK range, see below. If you have a TT and have increased the performance of the engine over stock then you should consider replacing your spark plugs with ones more suited to the performance level you are now running at. The table at the bottom should help you decide which model, heat range and gap you need for your application.


Q. How often should I change my plugs?

A. Copper based (standard) plugs 4-6,000miles

Platinum 25,000 miles

Iridium 30,000miles


Q. How much are they?

A. Copper plugs are ~£2 each

Platinum plugs are ~£6 each (not £14!!)

Iridium ~£8 each


Q. Why are there different heat ranges? Which one should I use?

A. Part of your spark plug’s responsibilities, in addition to firing a spark, is to remove heat from the combustion chamber. This is accomplished by channelling the heat through the insulator material and metal housing. From there, the heat is transferred to the cylinder head where the engine cooling system can go to work. A spark plug’s heat range is its ability to dissipate heat. The colder the plug, the more heat it can channel out of the combustion chamber. In a performance application, colder heat ranges may be necessary to handle the extreme temperatures brought on by higher compression ratios, forced induction, and high RPM’s. While colder plugs may seem to be the way to go, please remember that the spark plug must achieve its self-cleaning temperature where it can burn off fuel and carbon deposits. Otherwise, the plug could foul out where it is prone to misfiring and poor acceleration. A plug that is too hot can overheat, also causing power loss, detonation, pre-ignition, and possible engine damage. A good, general rule of thumb is to start with the factory recommended heat range. For every 75 to 100 hp you add to your engine, you may go to the next colder step.


NGK and Denso use different heat range grading systems they are;

NGK Heat Grade Denso Equivalent

5 16

6 20

7 22

8 24

9 27

10 31


Q. Iridium’s are very expensive, what benefits do they have?

A. Until recently, platinum was considered the best material to use on the top of an electrode because of its durability. However, Iridium is 6 times harder, 8 times stronger, and has a melting point 1200 degrees higher than platinum. Put that into a harsh environment such as an engine piston chamber, and you have a spark plug that can resist wear much better than platinum. Iridium's extreme durability has also allowed NGK and Denso to develop smaller centre electrodes (0.6mm and 0.4mm respectively). This reduction in size, from a standard copper plug's 2mm electrode reduces the voltage requirements to jump the gap and create a spark. Denso and NGK recommend their Iridium’s only be replaced every 30,000miles (in some applications iridium plugs will last 120,000miles BUT NOT A SPORTSCAR!), and this is 5 times the life a copper plug.


Q. What's the difference between the BCPR*ES (3330) and the BKR*E (6097) that get recommended a lot?

A. These 2 plugs are IDENTICAL in operation and completely interchangeable. But, the BKR*E is the recommended fit. One difference is that the BKR*E has an ISO sized connector to the coil pack and the BCPR*ES has a slightly larger one. The other obvious difference is that they BKR uses a V-groove electrode and the BCP uses a flat electrode. I would recommend using BKR*E's first but switch to BCPR*ES's if you have an ignition problems as I believe tired coil packs that have seen many a change will be slightly stretched inside and will benefit from having a larger plug body to fit over.


Q. What about platinum’s?

A. The author, at this time is not able to give a view on their merits, but they are fine for stock applications, I don't know how well they perform under the stresses of up rated boost/power.


Q. Why do you need to GAP a plug?

A. First off, you must not attempt to re-gap an Iridium plug. Trying to do so will damage the plug's electrode.

For copper plugs...too big a gap will create problems on boost, the spark is literally blown out by the air pressure before it has a chance to ignite the mixture, resulting in a misfire. A decent sized gap must always be maintained though as too small a gap will create problems at idle

and reduce the efficiency of the combustion process. Only adjust a gap by 0.1mm at a time and retest...if you go below 0.6mm and still have a miss-fire on boost I would suggest there is another problem not related to the sparkplugs (unless you are not using a plug in the correct heat range).


Q. Which plug is best?

A. An Iridium plain and simple. They are of superior construction, are more durable, spark better. This is according to the Denso and NGK blurb. Scare stories about Iridium’s causing detonation are not accurate. What is correct though is that unlike the copper plugs that melt and stop working, Iridium’s will continue working and detonation will destroy the next weakest point in the chain (pistons etc). However, one note of caution, in the past some people, have found that the ceramic insulator inside the tip of Denso made Iridiums has failed and sent a chunk of debris into the cylinder...and into the turbo causing damage. There have not been many cases and I believe most cases were in highly tuned vehicles but it is worth noting. In my opinion I believe that these failures have been linked to the mapping or tuning of the whole engine. If Denso had made a bad product, a) by now they would have fixed the issue, and b) they wouldn't risk their reputation on it and would stop selling them (Denso are a huge OEM parts manufacturer). I am happy that a properly tuned car running safe AFR's will run Denso or NGK Iridium's for a long time with no dangers. If you are in the process of tuning or are unsure if you are getting det then I recommend you stick with Copper plugs as these are cheaper to replace if you do suffer det and destroy the tips.


Q. HKS, TRD, Blitz, GReddy etc all make plugs too, shouldn't I buy them?

A. No. HKS and TRD are definitely Denso made Iridium’s. I would expect that the GReddy and Blitz one's are too...you are paying for a badge only, there is no difference between an £8 IK24 Denso Iridium and £11 HKS S40i. £3 per plug premium? No thanks!


Q. What about other makes, you've only talked about NGK and Denso?

A. Denso are the OEM supplier to Toyota. They should be in a stock car anyway which is why their range specifically caters for the Supra. NGK are Japanese too and likewise have tried and tested plugs that are suitable for our use. Other makes such as champion, bosch etc may well produce something suitable...but it won't have been tested as much as the plugs I've recommended here. It's your engine, your choice.


Q. I've heard you can read plugs to see if you're running lean etc?

A. No you can't, not in an unleaded environment anyway. If you read the plugs all you will see is the evidence of it's last few seconds of use before switching off...so idle...which is closed loop and will be a perfect 14.7:1 afr unless your 02 sensor is up the swanny, but if it was the engine would not be smooth, it would be hunting for an idle and you'd know there was something wrong!


What to use when MAPPING?

A. Use only copper plugs when mapping. Iridium plugs should be saved for an engine that is already mapped and tested on coppers. This is because the mapping process is fraught with danger and that danger is det. Detonation will ruin a copper plug, but the engine will be kept safe. An iridium plug is much more immune to det and other parts of the engine can suffer long before the plugs do. Stay safe and use copper plugs when mapping!





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Plug selection

Note - This selection list does not take Nitrous into account. If you have Nitrous go one grade colder than this table advises at your boost/performance level.


Rule of thumb

Iridiums should always come pregapped correctly - altering the gap will cause damage. If you test the gap and it isn't correct return them to the stockist and check they got in the right version.


Normally Aspirated

NGK - Standard - BKR5ES-11 (2382) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

NGK - V-Power - BKR5EYA-11 (2526) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

NGK - G-Power Platinum - BKR5EGP (7090) - gap to 1.1mm

NGK -Laser Platinum - BKR5EP-11 (3440) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

NGK -OE Laser Iridium - IFR5T11 (4996) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

NGK - Iridium IX - BKR5EIX-11 (5464) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

Denso Platinum - PK16R11 - gap to 1.1 (but always check first)


Stock TT

NGK - BCPR6EP-11 - gap is already 1.1mm at the "-11" signifies they should be set to this already.

NGK - BKR6E (2756) - gap 1.1mm

NGK Iridium - BKR6EIX-11 (3764) - gap is already 1.1mm at the "-11" signifies they should be set to this already.

Denso Platinum - PK20R11 - gap 1.1mm

Denso Iridium - IK20 - leave gap alone


TT @ upto 1bar

NGK - BCPR7ES (3330) - gap 0.9mm

NGK - BKR7E (6097) - gap 0.9mm

NGK - Iridium - BKR6EIX or BKR7EIX - leave gap alone

Denso Platinum - PK20R11 - gap 0.8mm

Denso Iridium - IK22 - leave gap alone


TT/hybrids @ upto 1.3bar

NGK - BCPR7ES (3330) - gap 0.7mm

NGK - BKR7E (6097) - gap 0.7mm

NGK - BKR8E - gap to 0.7mm

NGK - BCR8ES (3330) - gap 0.7mm

NGK Iridium - BKR7EIX - leave gap alone

NGK Iridium - BKR8EIX - leave gap alone

Denso Platinum - PK20R8 - gap 0.7mm

Denso Iridium - IK22 - leave gap alone

Denso Iridium - IK24 - leave gap alone


Single Turbo/Big Twins @ upto 1.3bar

NGK - BCPR7ES (3330) - gap 0.7mm

NGK - BKR7E (6097) - gap 0.7mm

NGK - BKR8E - gap to 0.7mm

NGK Iridium - BKR7EIX/BKR8EIX - leave gap alone

Denso Iridium - IK24 - leave gap alone


Single Turbo/Big Twins @ upto 1.8bar

NGK - BCR8ES - gap 0.6-0.7mm

NGK - BKR8E - gap 0.6-0.7mm

NGK Iridium - BKR8EIX - leave gap alone

Denso Iridium - IK27 - leave gap alone


Single Turbo/Big Twins @ 2+bar

NGK - BCR8ES - gap 0.6mm ??? UNTESTED

NGK - BKR8E - gap 0.6mm ??? UNTESTED

NGK Iridium - BKR8EIX or BKR9EIX? - leave gap alone ??? UNTESTED

Denso Iridium - IK27 to IK31 - leave gap alone ??? UNTESTED



Information sources




Personal experience

Previous discussions on this and other BBS's.

Edited by Steve (see edit history)
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Meant to ask ... does having a DLI make any difference to the gapping?


No it doesn't. It's supposed to extend the dwell time of the spark for better combustion. Im not actually sure though if it works...


I do not know about CDI systems either such as the AEM or Autronic. But my hunch is that the spark plug is still working in the same conditions no matter what voltage delivery system is attached. So the above should work on all modified ignition systems.


Terry maybe able to clear this up as I think he used CDI on his old one...

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With clever people like Alex and Ian C on this forum, its a god send!



Stop you'll make me blush! lol :D :thanks: :thanku:


Cheers guy's glad it's of use...but if there is other questions please ask here before I get the thread moved into the FAQ section. The more detailed it is the better...


And if anyone thinks I've got anything arse about face I don't mind being told so....always happy to learn.

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Guest Terry S

only thing I would say is the statement about iridiums causing det. I have never seen this statement, but from our experience the Denso iridium doesnt like detonation, and can break the ceramic, which in turn can drop into the cylinder. This maybe an extreme case scenario.


Alex are BCPR8ES' available readily?

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I'll add in about the ceramics but at the time I didn't cause I was wondering if it was a HKS version thing only...(ie blowing apart my HKS plug is the same as the denso part line) or if the Denso's themselves were known to break up too...


I didn't think the above was finished :) Been waiting for pointers like this :)


No idea on the plug availability front.

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Guest Terry S
So what's the answer? HKS only or Denso and HKS... :)
as above ;) The Denso Iridiums dont like det. Can say fro the HKS Version as they are too expensive for waht appears the same thing
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  • 3 months later...

Just saw this post Alex - a good compilation but I don't think NGK coppers need such small gaps at BPU level - 0.9mm is fine IMO for up to the 'safe' ackowledged upper limit of 1.25 bar boost. Also, you're right about the BCPR*ES range being JSO and so very slightly longer than the ISO fit BKR*E range but there are also a couple of other differences - the BCPR*ES range have a copper core whereas the BKR*E range do not, and the BCPR*ES range have a flat electrode whereas the BKR*E range have a 'V Groove' electrode.


About Iridiums - I'm of the opinion they are more fragile than coppers in a tuned turbo car situation and more likely to fail when the engine is detonating. There's nothing factual in this though, only gathered from a few friends of mine's unfortunate experiences with iridium plugs and the fact is the engine shouldn't be detonating in the first place so not really the fault of the spark plug.





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  • 7 months later...

Hi, I just wanted to know if the prices Toyota quoted me today for spark plugs and oil filter seem reasonable or is Mr T at it again :eyebrows:


Oil Filter: £7.39 + Vat & was told its a Denso one (oil filter) :blink:

Spark Plugs Denso (PK20R11) - £9.27 + Vat (each)


any help would be great :cool:

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Are PK20R11's not platinum though, and thus very pricey?


No real point going for these Supe, go copper NGK's for cheapness or Iridiums for longevity which are also cheaper than the platinums quoted. You also need to pick your heat grade according to your mods / planned mods!





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  • 5 months later...
Alex my Toyota Supra manual lists 2 plugs for the TT


NipponDenso PK20R11 (same as in the FAQ)




NGK BKR6EP11 you have put BKR7E (6097)


I`m sticking with the NipponDenso but wondered about the NGK ?



:p :D :rolleyes:


Classic newbie mistake ;) :p :D :rolleyes:


That's fine if you only ever intend to keep your car standard and run standard boost levels. Toyota will charge you around £70 or more for 6 of either of the above plugs. Both are standard heat range platinum plugs, the 11 on the end of both model codes indicates they come pregapped to 1.1mm.


The NGK model code indicates heat range six (standard) and P for platinum, then has the pregap tagged on the end. If you wish to go BPU and run more boost, it's standard practice to go one heat range colder (seven) running common NGK plugs (hence no platinum letter tag) and gap them down to 0.9mm - hence NGK BKR7E are the recommended - these don't come pre gapped hence no 11 or other numbers tagged on the end of the model code. These come in around £10 for a set of 6 from most motor factors and should be changed every second service.





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Happy with the car standard at present.


I`ve posted this elsewhere but I`ve sourced the Nippon Denso Platinum plugs for £45.95 for 6 inc vat.


Contact James or Mr Paul Wheatly

Westlands Toyota

Brettell Lane



01384 393047 or direct line to spares is 01384 393530


Tell them you`re a club member and get between 20 and 30% of retail price for Toyota Spares.

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