Spark plug #6 arching to block
 

So changed headers a year ago but haven't really used the car much since... at the time I bought a set of inexpensive wires for the 90 degree boots. After a new 5 spd swap to my 5.0 1992 TPI z28 and then a new rear end, I took the car out for a weekend that ran great. Then this week a misfire occurred lightly, then dramatically over the week. I only changed a couple of wires and left some old. I tried changing back to the old wires but same issue. With the lights out it appears to only Arch to the block at #6 cyl.

could it just be wires? Tune up? The t5 swap? Or blown cylinder?

Re: Spark plug #6 arching to block
 

Still running the automatic 7004r chip on the 5.0 for fyi

Re: Spark plug #6 arching to block
 

Cracked spark plug, If wires are good.

Re: Spark plug #6 arching to block
 

Here's a nice example of a plug that was arcing for a while.

Side 1:
Attachment 316683

Side 2:
Attachment 316684

If the plug had less miles on it, it might not have been as obvious. It didn't show on the engine scope either. Misfire eventually got worse as the mileage accumulated to where I actually felt something was wrong. This eventually killed my catalytic converter.

Re: Spark plug #6 arching to block
 

Thank you each for the responses. I think it's time for a tune up anyway so best to knock it all out