non resistor spark plugs

[wdfifteen]

I've completely given up on finding original Bosch W200 T30 spark plugs for my 912 engine. The new replacement would be W 6 BC plugs, but everywhere I look offers only WR 6 BC resistor plugs. My plug connectors include resistors and I'm afraid of eventually damaging the coil if I add more resistance. Does anyone have a source for non resistor, Bosch W 6 BC spark plugs?

[jhoagg]

I've been doing a similar spark plug search lately, and this may help. Take a look at this:

http://e28-535i.com/upload/Bosch_NGK_cross_ref.pdf

It says the NGK BP6HS is a direct replacement for the Bosch W6BC. Advance Auto (of all places) has these NGKs. Search for the NGK number on their website (specify "all vehicles") and it should come up.

[911pcars]

Coil damage is unlikely with more secondary resistance. However, + resistance = voltage reduction. If no radio interference, I'd gradually reduce/delete resistance in the secondary circuit. For example, high quality metal conductor spark plug wires should last a long time. On my last engine, the stainless steel, silicone jacketed wires on it were good for about 30 years until I sold it a couple of years ago.

Sherwood

[Tippy]

More resistance is actually less strain.

[911pcars]

Originally Posted by Tippy

More resistance is actually less strain.

Please explain, "less strain".

If you mean less strain on insulators, you're correct, but other than using substandard materials, there's not a lack of standard materials that prevent good insulation properties.

OTOH, if you can get your spark plugs to fire with 4000 volts instead of 10,000, adding more resistance to a high voltage ignition system isn't going to be a issue.

Thanks,
Sherwood

[Tippy]

Your 2nd point was my point.

[911pcars]

A good read:

"The Secondary Resistance affects secondary current and overall efficiency, with also a limited affect on rise time. The greater the secondary resistance the slower the rise time will be. But more importantly is that the greater secondary resistance lowers the maximum spark gap current, and drastically affects the coil's overall efficiency."

and....

"One item that many people do not know (or refuse to believe due to the absurd advertising they have been exposed to) about ignition systems can be said in a relative simple sentence, "The spark energy that leaves the coil and reaches the spark plug, jumping the gap and igniting the fuel mixture, is only going to be enough to do just that, no matter the coil's output rating." What that means, is that it does not matter if you had a bazillion-volt coil on your vehicle, if it only took 10,000v, 20,000v, or 8,000v to jump the gap and ignite the fuel mixture, that is all you're going to get on that cycle."

https://www.centuryperformance.com/forum/showthread.php/40-Ignition-Coil-Tech

Sherwood