Need help with a spark plug choice. I have 540's with 871's and EFI. Motors are dialed in but are rough on plugs. Heads are Dart pro 1's and currently running NGK -8's. What's a good plug to run in Blown engines. Thanks

Use NGK 5671A-7. The stocking item # 4091. I just put these in my new PRO1's after reading Eddie Youngs post.