TechTalk Bosch spark plugs_range_2021

Published on April 18th, 2021 | by Daniel Sherman Fernandez

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Are OEM Spark Plugs The Best For Your Car

Not all the time and we get an expert after sales person sharing their views on spark plugs.

Thinking about buying OEM (Original Equipment Manufacturer) or factory approved spark plugs for your car …. think again, for less money you could get a better set of spark plugs for your car at some times even just half the asking price!

Car manufactures do not always specify the best possible plugs when you take your car in for servicing but rather economic consideration often rule the day and sadly at times it is just sufficient and nothing more. 

That might be alright but not at the price you are paying for which can easily pay for a set of superior grade plugs boxed in the plug manufacturer’s own packing rather then the vehicle manufacturer’s packing. 

BHP_Euro5 Diesel_2021

Why pay double for essentially a box with the car brand on it. No vehicle manufacturer in the world make their own plugs, they all procure (purchase on consignment) from global manufacturers like NGK, Denso, Bosch, Champion, Brisk and KLG to mention a few. 

Using the spark plug manufacturer’s application catalog will assist you to get the correct upgrade plugs for a lot less and your car engine will love you more. 

Pictured below are two example of upgraded plugs …. one is single iridium and the other is double iridium from Denso. 

The double version gives the best burn velocity and requires the least energy to jump the gap and it last the longest with little gap growth, but the single type is better suited to force induction engines, being more robust. 

Both of these plugs reduce idle misfire to almost nil especially the double iridium type and it is fantastic in solving lean burn misfire in some direct gasoline injection engines which typically run ultra lean air/fuel ratios at idle and off idle to save fuel, these stratified charged lean burn designs require precise gas flow pattern to gather a rich mixture at the spark plug tip to initiate ignition and spread to the outer periphery’s homogeneous lean mixture.

This is fine when the engine is new and the intake ports n valves are free of carbon deposits, but with high mileage GDI engines, it tends to develop much more carbon/soot in the intake ports and this spoils the precise air flow pattern to achieve stratified fuel mixture at the spark plug’s tip and consequentially causes misfire every few cycles which affects idle stability and in bad cases off idle hesitation and stumble. 

The double fine electrode iridium helps mitigate this by improving ignitability thus improving idle quality, fuel consumption and more importantly, throttle response. A test on an unstable idling Alfa Romeo JTS direct gasoline injection engine clearly improved its idle quality by at least 70 percent. The other 10 percent improvement could be had from a set of new O2 sensors as aged sensors having a slower switching speed causing less precise mixture control in the feedback loop. 

We suggest that you research and decide against OEM spec spark plugs and try and use a better one, especially since it is sold at a lower price.

Many official workshop staff will frighten the less informed of engine damage if they use non standard OEM spark plugs’. Get the correct reach, size, heat range and cross referencing to the application catalogue and you are good to go.

Bosch spark plugs_range_2021

This message above had been shared by a retired experienced vehicle engineer.  

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