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spark plugs for 964 C4 3.8 mod 89


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I´ve the following modifications:

3.8 engine forged pistons 11:4

perfect bore 102 cilinders

rs cams

titan valve retainers

special valve springs

cup pipe

no cat

dme remap

95 oct gas

Bosch FR5DTC spark plugs!!

the engine runs realy B) :) .

I would like to know if you could recomand me another typ of spark plugs for better performance?

thnx in advance


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  • 3 weeks later...


first you should contact the engine builder and ask them for there advice. The 3,8L Conversion was done by the factory and some tuners as well. However while they mostly used the same hardware they can have different CC Ratios in the Head and therefore different Compression Ratios. While the Knock detection will prevent missfire it will not detect a hot spotet Spark plug melting down into the engine.

Bosch is a good brand but i prefer the more trouble free NGK (BCPR7ET/BCP7ET), Champion (RC7YCC) or Beru (14FR5DTU) Brand.

If there is any trouble with the ignition you can try to use Bosch F5DTC without surpression Resistor.

The F5DTC works better under lean conditions and seems not to foul as fast under oil in the combustion.

Both are issues with old & worn engines but mostly the NGK oder Beru work with resistor as well and they are much cheaper to have.

While Porsche intruduced the 993 they swaped to FR6DP Plugs for extended Service life but soon replaced them with FR6LDC from the 993TT.

For extended Service live the NGK BCP7ET worked very well on stock engines and will fire much leaner mixtures then the stock spark plug. However Porsche Factory Service don´t recommend the 3 or 4 Tip Plugs as as the spark will not ignite on the correct spot wich translates into retarded ignition and less peak power.

Porsches don´t likes the Brisk as they seem to have much shorter service life the the maintenance scedule and they tend to "stick" in the head risking expensive treat repair however mostly you also find someone greased the plugs at the last installation.


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