TheSamba.com :: View topic - Spark Plug Gap and Resistor vs Non-Resistor

Sun Feb 03, 2013 4:28 pm

I just put new heads on my 71 stock (no performance upgrades) dual port 1600 engine. The previous owner was using Bosch W8AC plugs with 1/2" thread lengths in the old heads. My new heads require a plug with 3/4" thread length. As best I can tell I'm running a stock coil and good quality Bosch spark plug wires.

I've spent several hours reading spark plug related info on the web and this site. Apparently, there are many plugs that would work and a lot of people have an opinion about which one is best. I'm considering the following: NGK B5ES, NGK BP5ES or Bosch WR8CC.

If I don't go with the Bosch resistor type plug do I run the risk of picking up spark interference in my stock radio?

Is the gap setting dependent on the type of plug I select or should I stick with the .024" gap published in the Bentley manual regardless of the plug?

In case it is helpful I did come across this site that demystifies the spark plug codes for NGK, Bosch and other brands: http://www.gsparkplug.com/shop/spark-plug-manufacturers-code

Sun Feb 03, 2013 4:52 pm

Neither of those NGKs are resistor plugs, but the Bosch is.

I personally run non-resistor plugs, I see it as one less thing to worry about breaking down. I haven't had problem with interference, but I don't have anything to fancy in the electrical department.

the NGK BP5ES has a projected tip, I don't know how that affects anything but I would go for the non-projected tip just because that is closer to stock.

You would gap the spark plugs to .024 as it has more to do with the amount of spark the ignition coil is putting out then the spark plug receiving it.

Mon Feb 04, 2013 8:10 am

Quote: Bosch resistor type plug
There are already lots of resistance in the stock ACVW high voltage circuit. It's in the 'carbon' brush in the center of the dist. cap. There's the resistance built into the rotor button. The wires have some. The wire ends that push onto the threaded plug ends have resistance built in. I'm willing to bet you won't hear any difference in the sound quality of the radio going with non-resistance plugs. :wink: