by 
The Curious Bag
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<h4 class="dechead">On One Hand: Not According to Consumers
Bosch spark plugs are significantly less expensive than NGKs, and it shows, according to consumers. Drivers report a variety of problems with Bosch plugs, including loss of power and gas mileage, poor idling, and deceleration surging. Spark plugs made by NGK, which is headquartered in Japan, are higher quality, especially for use in high-performance vehicles.
On the Other: There Is No Proof
There are no scientific studies that compare the two. Both last around 60,000 miles. An amateur test was performed in 1999 by a motor sports enthusiast comparing the two. The test was very faulty because used Bosch plugs were compared against new NGKs, and the engine temperature was different. Nevertheless, the Bosch plugs performed as well as the NGKs in that flawed experiment.
Bottom Line
While there is no scientific experiment that compares the two, consumers report that Bosch spark plugs are not better than NGKs. They are just as good, as long as they do not cause any problems.
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