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I have a '75 Convertible with a 350 carb engine. Going to change plugs this weekend and need the plug gap information. The Chilton Manual says .060 for the1975....but all the years before and after shows either .035 to .045. WHICH ONE SHOULD I USE????
For model year 1975 with the originally equipped engine, the correct spark plug gap is 0.60". The correct spark plug is an R-44TX ACDelco spark plug.
but was that .60 just because it was the first year for HEI and they learned and revised the gap for the following years that used the same components or is their something unique about the ignition system on the 75? if so what is it? the OP's ignition / distributor system does not appear to be original either so Not sure if the stock specs even apply here?
I've been running .050" in my 77 with HEI and it seems to like that. I believe my manual also say's .060" , That's a bit much IMO may encounter misfire at high RPM or with highish compression. If it's stock it'll probably take it.
but was that .60 just because it was the first year for HEI and they learned and revised the gap for the following years that used the same components or is their something unique about the ignition system on the 75? if so what is it? the OP's ignition / distributor system does not appear to be original either so Not sure if the stock specs even apply here?
augiedoggy it is above my pay grade to try to figure out why technical elements of the Corvette evolved the way they did 46 years ago. I know of nothing unique about the 1975 HEI system as compared to later years such as 1976 or 1977, other than the spark plug change. I did notice that the plugs specified were changed for model year 1976 to R-45TS with a specified gap of 0.045". Emission controls systems continued to evolve in 1976 from 1975, so maybe the hotter plug with a smaller gap eliminated the need for an AIR pump in certain applications for 1976. The mysteries continue.
The wide gaps are to improve performance with leaner emissions mixtures. The wide gaps were required to fire the crappy, harder to reliably fire mixture....the HEI was required to fire a plug with a wider gap.
Spark Plus Gap 1975
