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Spark plug recommendations for normally aspirated '95

Joined
11 January 2021
Messages
550
Location
Ontario, Canada
I've searched and I can't find an up-to-date thread on spark plugs for normally aspirated engines. The local Canadian Tire has about 10 options and RockAuto has even more! I'm not interested in saving a couple of bucks on my NA1 NSX.

With all the platinum/iridium/e3 plugs out there, what goes in my 25-year-old NSX? Searching for my part# from the manual has got me nowhere, discontinued. If the Iridiums are actually any better, I'm glad to spend the $. The iridiums are $12 and Platinum $6.5, so the difference is only $33, nothing compared to the value of the time changing 6 of them. I just want to be sure they won't be bad for the engine since it was designed before they became available. On the other hand, a spark should be a spark based on the voltage, gap, and impedance of the air/fuel mixture?
 
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Plugs

The OEM NGK plugs are the best. You don’t get enough performance upgrade for a non race engine to justify the stupid cost of “iridium” plugs.
Stick with the OEM plugs except you “might” want to change the temp range of them because of the operating temp where you drive your car the most.

Cheers
nigel
 
I've searched and I can't find an up-to-date thread on spark plugs for normally aspirated engines. The local Canadian Tire has about 10 options and RockAuto has even more! I'm not interested in saving a couple of bucks on my NA1 NSX.

With all the platinum/iridium/e3 plugs out there, what goes in my 25-year-old NSX? Searching for my part# from the manual has got me nowhere, discontinued. If the Iridiums are actually any better, I'm glad to spend the $. The iridiums are $12 and Platinum $6.5, so the difference is only $33, nothing compared to the value of the time changing 6 of them. I just want to be sure they won't be bad for the engine since it was designed before they became available. On the other hand, a spark should be a spark based on the voltage, gap, and impedance of the air/fuel mixture?

Can't ever go wrong with OEM. One of these is all you need. :

98079-5617TSPARK PLUG (PK20PR-L11)6$54.62DENSO-OEM Double Platinum Spark Plugs
98079-5617TSPARK PLUG (PFR6N-11)6$84.33NGK- OEM Double Platinum Spark Plugs

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Can't ever go wrong with OEM. One of these is all you need. :

98079-5617TSPARK PLUG (PK20PR-L11)6$54.62DENSO-OEM Double Platinum Spark Plugs
98079-5617TSPARK PLUG (PFR6N-11)6$84.33NGK- OEM Double Platinum Spark Plugs

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Thanks for the replies! Perhaps the problem was the way I was searching for them. That is the part # I found in my diagrams and was looking for, but Amayama shows it as discontinued without suggesting a replacement, as does my local Acura dealer. (Canadian Acura is starting to get brutal with part supply. July 15 delivery for a new coil. :mad: I have to order everything from USA or Japan.) With the PK#, Amazon has them, but more expensive than NGK iridiums, and with poor reviews. It's also available from oemacuraparts now for Can$25/plug. The only double platinum plug that fits and I can get locally is Champion brand, but I'd prefer Denso or NGK, and they only had 4 of them anyway. I wound up buying 6 of each of the NGK iridium BKR6EIX11 and the regular platinum BKR6EGP to avoid any delay. I couldn't stop myself from trialing an iridium plug for diagnosis of the stumbling that led me on the original spark plug quest. For $12, I confirmed the spark plug as my original problem, CEL no longer coming on and uneven idle resolved. I now need to decide whether to replace the other 5 with NGK iridium or order 6 Denso double platinum, for higher cost, delivery in several days from Amazon. Everything I've researched seems to suggest that iridiums are at least as good as platinum, so I'm leaning towards iridium, since they're right here in front of me now.
 
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I expect that your part number mystery relates to the fact that I think the 'part number' reflects the packaging. The PK20PR L11 (the number with the useful heat range and size information) is what Denso calls the long number. 3142 is the Denso stock number for single spark plugs with that long number. Different vendors have different stock / part / inventory numbers for the same plug if they are packaged differently such as in boxes of 4 or 6. The 'part number' thing is further confused by the fact that the car manufacturers will assign their own part number to the plug for the OEM specific plugs so you can have a Denso stock / part number and a Honda part number. I picked up 6 of the OEM spec Denso double platinum from Rock Auto for about $5 Cdn when they were on sale and just shelved them until I needed them.

You have the correct iridium heat range and size for the NSX. NGK iridium is actually the OEM plug on my Son's RSX - kind of choked him when he dropped close to $50 for a set of four when he was on a 'university budget'. I use iridiums on a vintage car because NGX does not offer conventional platinum plugs in the correct size / heat range and they work just fine. I don't know why the iridiums would get poor reviews unless people were expecting a performance increase associated with them which is not going to happen. Magic metal plugs are all about extending the life span of the plug and maintaining performance . The fine wire plug (compared to conventional fat center electrode copper plugs) does have the advantage that they fire at a lower voltage and are more resistant to fouling. That is useful on 2 stroke MX bikes. Not so useful on OEM spec engines where the AFR is tightly controlled to 14.7. Their fouling resistance means you can push a colder heat range if you are running a high performance engine with carbs that are less than perfect at maintaining a correct AFR.

I am personally disinclined to mix and match. 5 new NGK iridiums would be about $60 and 6 Denso double platinums from Rock Auto are a nudge under $50 before shipping. The only engineering reason I have to avoid mixing is that the Denso 20 heat range may not be exactly the same as NGK 6. The NGK double platinums are the same price as the NGK iridiums so I would stick with 5 new iridiums if you want to stay with NGK.

As a final observation, unless you know who is supplying the spark plugs via Amazon I would purchase from RockAuto or Canadian Tire or some other main line vendor. I don't know whether it is still prevalent; but, a few years ago there were vendors selling counterfeit versions of NGK and Denso platinum and Iridium plugs; but, made without the platinum or iridium. They worked; but, wore out really fast. A large vendor like RockAuto is more likely to have a non dodgy supply chain than the XYZSPARKY spark plug vendor on Amazon.
 
Thanks. Definitely no plan to mix & match; I just put that single new plug in as a test on a bad plug. If one went, the others can't be far behind, so I'll change the other 5 as well. I originally bought 3 2-packs of the NGK iridium IX from Canadian Tire. Just questioning whether to return 2 unused pairs (2 to a pack, one pack is already opened) and get 6 double platinum Denso from Rock Auto, or just install the other 5 NGK iridium IX's that I have. $ will basically be a wash, $48 back but $49+shipping, but if the Denso double platinums would be better, I can wait on Rock Auto.

To clarify my post above, the poor reviews were for the double Platinum plugs on Amazon, perhaps related to counterfeit product? The iridiums had good reviews.

What confuses me about Rock Auto is that they list Denso 3142 as the double platinum option, but the spec sheet shows Heat range 20?? The NGK iridium plugs they show are 6741 Laser iridium, or NGK 3764 iridium IX, both heat range 6, which is what I thought I needed. And, for good measure, the chart at Rock Auto claims "more power and fuel economy" for iridium plugs. Uh huh. The chart also says Iridiums will last longer than double platinum, which I do believe. I'd like more power and fuel economy. :wink:

It's hard to believe the double platinum plugs will be that much better than the NGK Iridium IX's that I have so I might as well just put them in.
 
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To clarify my post above, the poor reviews were for the double Platinum plugs on Amazon, perhaps related to counterfeit product? The iridiums had good reviews.

What confuses me about Rock Auto is that they list Denso 3142 as the double platinum option, but the spec sheet shows Heat range 20?? The NGK iridium plugs they show are 6741 Laser iridium, or NGK 3764 iridium IX, both heat range 6, which is what I thought I needed. And, for good measure, the chart at Rock Auto claims "more power and fuel economy" for iridium plugs. The chart also says Iridiums will last longer than double platinum. I'd like more power and fuel economy.:smile: It seems like I should just go with the NGK Iridium IX's that I have?

There is no standard for heat range numbers. For both Denso and NGK, as the number goes up they become a colder plug. However, for Bosch and Champion as the number goes up they are a hotter plug. Denso 20 and NGK 6 are approximately the same heat range and both are recommended applications in the NSX service manual.

DensoProducts.com: Heat Range Conversion Chart

I don't expect that a fresh set of iridiums versus a fresh set of double platinums will yield any performance differences. The iridiums will likely provide good performance longer; however, I expect that most NSX owners do not run their plugs long enough such that deterioration is going to be an issue. For what it is worth, I ran the factory platinum spark plugs in my 2003 Honda Pilot to just under 90,000 km. When I pulled them out they looked really good. The benefits of digital fuel injection systems that run tight AFRs.

Going with a full set of the iridium plugs will never be a bad choice, especially if you can source them locally.
 
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