steve6

soo.. I bought a 87 convertible. Runs a bit rough at idle but has had engine work (cam'd for sure, not sure of any details), not soooo bad when warm, but I can feel a mis-fire driving sometimes.

I bought 8 plugs (model according to the book), figured a good place to start. I took the plugs out of it, changed a couple and realized, wtf different length? The new ones are longer, much longer. Would this year vette ever have short plug holes as an option?? I am pretty sure that someone ****ed up, they are nice NGK platinum, but being so short just does not make sense.

https://www.dropbox.com/s/cyx0nn4y0v...2019.19.12.jpg

I tried to get a picture of how deep the hole was... You can almost see how shallow the old plug went...

https://www.dropbox.com/s/entf7kmrtv...2019.20.15.jpg

what do you guys think? Ok for the longer ones? The replacement are a champion platinum.

captainkawasaki

87 convertible would have had factory aluminum heads using the long thread section spark plugs. Short thread section plugs are for cast iron heads. You say there was engine work, stick a magnet on the heads and determine if iron or aluminum, then use the appropriate depth plug.

John A. Marker

Should be aluminum heads that require longer plugs. be sure that they are actually aluminum heads and put a magnet on the head. If it sticks, the heads are cast iron and use a shorter plug. If they are aluminum then use the longer plug. The shorter plug may have an influence on your miss fire. When it is dark out, lift the hood and disconnect the lights under the hood and start the car. In the dark....look for any arcing from any of the plug wires. Wires could also be an issue.

steve6

I changed the plugs.. much better

John A. Marker

Aluminum does not rust.....test head with magnet. If you went with the longer plug and the heads are cast....the plug might be too long.

steve6

They are aluminum, I checked with a magnet, but there really isn't many spots to actually stick a magnet too with the headers on it.