i alternate between 3924's and 3926's for street driving. 3923's or 3921's would be a good starting point for racing.

$20 NGk's. Used all those expensive race plugs for as much as $50 a set.No better than the regular NGK's

looks rich, would hope that's not a top end shutoff?

Denso makes good plugs. Never used them in an old car though. Use ngk mostly. Used to go with autolites before they decided to import them. If im going to buy import anything, it will be good stuff.

NGK or Denso in my vehicles, only use champions in my lawn eqipment when I can't find NGK or Denso

I'm freshening my 572. It made its best passes ever at the end of the year. Went 9.02@151, 3350. I guess it'll get a new set of NGK's. The old ones have 300 passes.
Doug

actually, i don't get too lost in the name brands, look for something that has a tip that fits the combustion chamber, proper heat range, not too much resistance (i ohm check plugs), and go for it. i did do an ohms check on a champion rc12y vs an autolite 3924. the champion had 70,000 ohms resistance, the autolite had 7,000 ohms. i double checked, i tripled checked, couldn't believe it at first.

NGK has a real tech guy that answers on second ring --he will put you dead on with a plug part number all are about $19 a set off Egay with free shipping and if in a jam Advance Auto parts can get overnight for decent price.
Thing is with NGK the plating used on the threads makes good tuning aid--we run alky and when we get that plating burning off a couple threads up then we are dead on
NGK quality is second to none. I do like Autolite race plugs but for the money no way I will swap from NGK--I would not take a set of Champion junk plugs for free--usually hard to get 8 out of the box w/o one being fubar'd up with off center etc
NGK 5671A then select heat range number 7-8-9 etc and away you go Hands down best plugs year after year Japan made--awesome quality plug after plug

The China Autolite street plugs were awful--but they have switched back to Mexico and quality went way up--if buying Autolite street plugs do NOT accept any with China on the box--even the threads can be twisted and bad on those like they were hand done with worn out leftover WW 1 Russian dies

Most plugs for magneto applications should only be 5K ohms max. Most I get are in the 1.5k ~1.9K ohm range. Tim

I ran Autolite race plugs in my 12.5 440 street motor.It runs Stealths and Dominator on the street.They were decent but just didnt feel right.Went to NGKs like 4 or 5 years ago.Still the same set and runs great.idle seems to be better also.Rocky

Champion "R" plugs are resistor plugs. Thus the high resistance.
Doug

If you are fouling plugs........the ignition is weak, you have the wrong heat range plug, or the carbs are off

I use the Champion race plugs with the cut back ground strap in all of the "race" engines that I work on. I've never had an issue with any of the Champion race plugs. I can't buy them locally but Summit always has them in stock so I just keep an extra box in the drawer.

I'm running NGK plugs in my pump gas 470 engine. At the moment I'm trying the projected and the super projected plugs just to see if it makes a difference.

I agree that Champion Race plugs are fine except the price $4 a whack
NGK offers same kind of ground straps / non projected tips etc for $2 a whack

FWIW I understand that the projected tip plug was invented by Smokey Yunick
( as well as cross flow radiator and other gems we take for granted)

If I am remembering correctly, my NGK salesman told me they now make Autolites. Hope this is not misinformation...

I sure learned that the hard/long way,,,,,,

i just did an ohm check on a autolite ap3924; 5000 ohms. there's an autolite 5224 that has a longer projected tip. all down at wally world!

Champions lasted for 1 meet for me with MSD6A, rubbish, went to NGK 7's, never looked back, far superior.