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I'm about to do a tune-up on my new-to-me 85. The Owner's Manual says "AC Type R43CST (.035 gap)" . My understanding is that AC Delco R43TS is the successor part number. I bought 8 and they are pre-gapped at the specified 0.035".
However, I just noticed the Emissions label under the hood and it states the gap as .045".
Questions: Did I buy the right spark plugs, and which gap will be better for performance?
Follow the instructions on the emissions sticker.
i would take the plugs back and get different ones.
if you spread the gap to .045, the ground electrode Probably will not line up parallel to the positive electrode without excessive bending.
the reason you have .045” gap is because your engine has HEI distributor. It puts out a healthy spark (up to about 6500 RPM) and helps to more completely ignite the fuel mixture.
.035 is for point type ignition systems and weenie foreign cars
😂
Spark plug gap it often misunderstood. In your case it doesn’t really mater but when you have higher compression and larger “wetter” fuel loads like in a race engine you need to reduce the spark gap. You could put the 0.030” plugs in and the car would run fine, you could take them back to the shop and swap them for 0.045” and the car should run fine provided it’s stock and the HEI is still putting out good solid voltage, or you could regap them but NGK recommends not to change the gap by more the 0.008” . If it was me I’d use the one you have with the preset gap.
Thanks all for the replies. I discovered that there was a Service Bulletin that involved failing coils, and one of the fixes was to re-gap the plugs to .035", and install a new label.
ServiceBulletin Number: 85C22
Bulletin Sequence Number: 089
Date of Bulletin: 8608
NHTSA Item Number: 86532
Make: CHEVROLET
Model: CORVETTE
Year: 1985
Component: ELECTRICAL SYSTEM:IGNITION:COIL
Summary: PRODUCT EMISSION CAMPAIGN 85C22 HIGH OUTPUT IGNITION COIL-DECLINING IGNITION VOL TAGE OF HIGH OUTPUT IGNITION COIL-MAY LEAD TO ENGINE MISFIRE, HESITATION, SAGS, OR NO RE-START-CORRECTION WILL CONSIST OF REPLACING HIGH OUTPUT IGNITION COIL AN D MODULE, REVISING SPARK PLUG GAP AND INSTALLING A SPARK PLUG GAP REVISION LABEL -ALL 1984-1985 CHEVROLET CAMARO MODELS WITH 5.0L V8 (RPO L69/LB9, 1985 MONTE CAR LO MODELS WITH 5.0L V8 (RPO L69), AND 1984-1985 CORVETTE MODELS WITH 5.7L V8 (RP O L83/L98) ENGINES
The car works really good, it's not modified or will be used on the track. I just want to refresh the parts by a tune-up, so I'll pull one of the plugs and measure the gap, and put the same gap in there. Based on the Bulletin, and the successor plug part number, I suspect that it is .35". I'll report back.
I wanted to loop back on this thread. I found that the existing plugs were gapped at 0.045". The coil was replaced as it was date coded to 1987, probably as a result of the above Service Bulletin. There were also 8mm Packard Delcore wires installed (not sure if they were original equipment or an upgrade with the new coil). This obviously worked for a long time, so I just re-gapped my new AC Delco plugs to 0.045".
I cleaned the spark plug holes well and put antiseize sparingly on the new plugs and torqued them to 17 ft/lbs ( 22 ft/lbs spec for an iron head x 75% for a lubricated application):
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
Spark Plug Gap (1985)
