I just did them on my 1988 and they were gaped at .45.. Just a heads up Racing Head Service® offers ZEX™/Champion spark plugs for use in nearly any street or race application. ... do you recommend a .035" gap on a 10:1 vortec headed TBI 355? Don't gap it at .060, try .045 to.050. Look for heads having a spark plug (or spark plugs from adjacent cylinders) with no unusually colored deposits- or a lack of deposits that were removed by coolant getting into the chamber(s). I need to get some new spark plugs. from Irwin, PA. Been searching a lot about this as I am switching my plugs out and changed to the AC Delco R44LTS for the vortec heads. This spark plug will be purchased preset from any auto parts store. What is the part number for AC Delco spark plugs for a set of vortec heads… And if you are going with factory AC delco plugs which work well in the Vortec motor then absolutely be sure you check. Technical Vortec Heads Spark Plugs. R42LTS - Stock and a good place to start. The original 305ci with the stock heads was .035" The newer vortec heads spec is .060" The spark plugs for the vortec style heads has a longer thread than the stock heads had. Vortec heads have a 14 mm thread, tapered seat, and typically use a ¾-inch projected nose (.750) reach, small (5/8") spark plug socket. Excessive changing of the spark plug gap setting will result in weakening of the spark plug ground electrode and can lead to breakage. Also, the spark plug gap should never exceed .055" unless pre-set by the manufacturer. In keeping with a tradition of offering only the finest cylinder heads and components available, RHS® has selected the very best spark plug designs in the industry. The spark plug they are using is with their kits is the NKG TR55. RHS® - Spark Plugs For All Of Your Street And Competition Needs! I would still double check the gap on them. Member. The spark plug gap adjustment should not be changed more than 3 times and should not exceed .008" in either direction. The AC Delco equivalent is R42LTS6. The spark plug gap for a Chevrolet Tahoe 5.7 350 Vortec should be set at .060 inches. says gap the vortec 454 plugs at .060, but I learned on the Full Size Chevy forum that gapping them smaller at around .045 to .050 gives you more power, smoother idle and eliminates a common miss or skip under load that was problematic on these engines. Joined: Apr 10, 2019 Posts: 22. Profile Page. I've got a set of Vortec heads on my TBI motor. 49StreetRod. I know G.M. Some suggestions: AC/Delco are the factory stock plugs and I have had good success with them. The guys at the parts store ask me what year truck... well, these heads don't come on a 93 Chevy, so I can't tell them that. Discussion in 'Traditional Hot Rods' started by 49StreetRod, Nov 13, 2020. 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