Spark plug choices
 

The car is a stock 1987 924S in rehab. It runs but has a mild flat spot in the middle RPM range. I have not replaced the plugs yet because they look good. There appears to be several choices (both standard and high performance) for this engine. The main difference appears to be heat ranges. Historically, I've had the best results with NGK in all my cars but if there is a consensus plug that has the best track record for this engine, I'm all ears. Thanks.

I always used what Porsche advises in the manual which is Bosch Copper WR7's. Maybe today there are better modern options idk, subscribed.

The PO had iridium plugs in the car. I changed over to copper after a while, and saw no performance difference. I say save your money and stick with copper.

http://forums.pelicanparts.com/uploa...1567794161.jpg


I like these in the '92.

Ngk bpr6es

Thanks for the help
 

I'll let you know if they help with my flat spot.

vacuum leak

Thanks
 

I have a smoke machine. I'll give that a try.

The WR7DC plugs are great. In any case, I would stick with copper. I go with the NGK BPR6ES plugs because they dissipate heat more quickly than the WR7DC ones.

Best results with NGK
 

I've had my best luck with NGK. I bought BPR6ES and will put them in right away.

I was surprised to learn that one of the most significant differences in spark plugs was its ability (speed?) with which it transfers heat from the combustion chamber to the engine head. So what's best for our 924s? This:

An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as adding a turbo or supercharger, increasing compression, timing changes, use of alternate fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature, necessitating a colder plug.
Source: https://www.ngk.com/learning-center/article/207/what-is-a-spark-plugs-heat-range

Not only that, the addition of Ethanol to gas and the effect on spark plugs was also addressed in a TSB by NGK.


http://forums.pelicanparts.com/uploa...1568208847.jpg

+1

I was always hooked on Bosch, but just installed NGK standard copper plugs (sparkplugs.com) that were one level cooler than OEM Bosch. It seemed that availability of various levels of heat range for NGK was better than Bosch, since I ran into Bosch heat levels that were discontinued. Several vendors also stated that QC seems better for NGK.

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1968 912