Spark Plug Heat Range

[HTSS_TR]

Why different spark plug companies recommend different heat range for the same engine ?

Honda S2000 OEM plug is NGK platinum PFR7G-11S, NGK website recommends that platinum plug and Iridium plug IFR7G-11KS. Both has heat range 7.

Bosch recommends platinum FR7DPX which is 1 heat range hotter than NGK. According to Champion Heat Range Conversion Chart: http://www.championsparkplugs.com/learning-center/article/225/heat-range-conversion-chart

Champion recommends RC6WYPB4 (Iridium), 1 heat range cooler than NGK.

Denso PK22PR-L11S is the same heat range as NGK.

According to Champion Heat Range Conversion Chart, the Champion plug that matches NGK Iridium IFR7G-11KS is RC8WYPB4.

I know the safest choice is go with OEM plug which is NGK platinum PFR7G-11S, second safest is NGK Iridium IFR7G-11KS. But I like to explore aftermarket plugs, Champion and Bosch make good plugs and I think their plugs are as good as NGK and can be bought for much lower price.

 

[kr_bitog]

It because of their plug construction material, the table is just estimation guideline and should not be taken as exact comparison.

Champion tends to have hotter plug specified for the same range, and who know what reason they specify 2 heat level for 1 heat level the other company use.
Probably in the past the plug fouled so much, but that is just my guess.

In my experience, champion is ok except the ceramic is more prone to break compared to Denso, NGK, Bosch.
Of course, with 7 year unlimited warranty, that may ease a bit of the worry. However, for me I switch to Bosch OE Iridium for value for money.

 

[supercity]

The numbers are not directly comparable. e.g. Bosch 6 is inbetween NGK 6 and 7

 

[VinceF]

I'd go by how the plugs function and look with use. I had a car that fouled a couple OE plugs after 3K mi, and every 600 mi after that. The car had 1-4bbl, and the Co called for the same plugs that were in the 2-4bl police motor. With a lot of city driving they would foul. Dealer tuned the car 3X, but wouldn't try a hotter plug. I did and solved the problem. I know that cars like cabs that idle a lot and drive slower like in a city use a hotter plug. Your car might be on the edge of being able to use either heat range. The car I mentioned could also run on a lower octane gas than called for. The compression ratio was 9-1 so not really high or low.

 

[dparm]

 

[Vikas]

Conventional wisdom is that you stay with OEM Denso/NGK on a Japanese car.

 

[ARCOgraphite]

What kind of ignition? dual coils or COP? If cop id go with a performance fine wire iridium to minimise3 light throttle misfire. A HR #7 sounds about right for a stock lambda feedback motor that gets prodded and cropped hard now and again. Mild passenger cars usually run the smog hot# 5(16). Our old 2.2L Subaru liked denso in a #22 and hated the OE BPR6es-11 garbage. The 93 Imp 1.8L EJ subie ran an OE HR #8 champion that was impossible to find - It wouldn't run on a 9 (.04gap). I kept cleaning and filing the champs to keep em going.

 

[dparm]

Originally Posted By: Vikas
Conventional wisdom is that you stay with OEM Denso/NGK on a Japanese car.



That myth needs to die. Plugs are plugs. My Integra, S2000, and Mazdaspeed3 all saw various plugs over their lives: NGK, Denso, Bosch, and Autolite. Never had any problems as long as they were gapped properly and the heat range was correct.

Same thing happens with the German car enthusiasts: they think only Bosch plugs are okay to run.

 

[Vikas]

I personally had problems with Bosch on my Honda but my experience is now decades old. When it started behaving, it took a long time before I was able to indict the Bosch for sure. These were the days when I used to change spark plugs too often on my carburated engine. I had used these platinum tipped Bosch before that incident, so I did not initially suspected the plugs. I removed the brand new Bosch and put back the old NGK and then the car ran fine afterwards.

Bosch was the first manufacturer to make affordable platinum tipped spark plugs available at that time.

 

[dparm]

Bosch also made plugs for NGK (but branded them as NGK) for a number of years. Little known fact.