Whats the best spark plug for a c-85

It's been a year since I stated I gapped my plugs to 19.  Since then, I found a Tempest chart that said 15.  I talked to my IA.  We agreed that 15 would be a good gap.  So, now I'm at 15 and have had no issues and it "SEEMS" to run smoother and "SLIGHTLY" more oomph.

I just cleaned, checked the gaps and rotated my plugs.  16-21 was what champion recommended...I sort of split the difference and decided on 19 since that is what they (all but one) turned out to be anyway.  If  I thought I could get better performance I'd definitely pull them again and regap to 16.

16 is what I'm going to set them at, I agree, a smaller gap has benefits for that engine, as it's almost at its limits in power now, considering what we are asking it do do. 85 HP isn't much, the carb, prop and plugs make a big difference in performance I know, and I've addressed all three of them, so lets see what happens now. Thanks for the advice.

16-21 per champion, you need a smaller gap because of the magneto, it does not put out as much current as the electronic ignition in your car.

Thanks for the info, but I have the champion REM 40E plugs and was told a gap of 17 is right, is that right? Seems a bit too close, but perhaps it should be? Does that sound right? I don't see that in my book, it says 16 to 21, but isn't specific.

Fine wires are the best, but also the most money, Massive electrode plugs work fine. If you want the best performance make sure the mags are in good shape and the timing is correct. If you have a chance when the mags are off the engine, turn the mag drive and feel the amount of magnetism in the rotor, it should snap into place when the poles are aligned, if you can barely feel the magnetism, the mags could use some work.