08-27-2017, 08:34 PM
The letter before the "S" is the reach. "H" means a 1/2" reach, no letter means a 3/8" reach. The "E" means 19.0 mm, and those are TOO LONG for any Mac kart engine. The "S" means copper core center electrode. For an early Mac with 3/8" reach, the B7S for gas, and the B8S or B9S for alcohol. On a newer 1/2" reach head like the later 91's or 101's, and for West Bend 610 or 820, B7HS for gas, B8HS or B9HS for alky. I've been running B9HS on modified alky engines for ten years. They are very long lasting and perform great. I don't know how Chuck Giacobbe's stocks are holding out, but I buy NGK's from him. He has good prices. Ted