[XfireZ51]

Here's the latest on my playing around with spark plug heat range.

First .jpeg shows ground strap heat range indication. Yoou can see that the color changes near or at the gs bend.

Second .jpeg shows the fire ring at base of porcelain. The plugs are (left to right),
BKR6E, AC 41-602, BKR7E, TR55XI. Looks like there's more fuel to take out at top end but I'll need to monitor KR and AFR using my WB. However, it tends to confirm that my suspicion is that the WB, at the tailpipe, used by the dyno operator is reporting lean.