I just had a set of stock rect port chev heads pulled off my 540 and replaced with 325cc Dart Pro 1 fully ported heads. What spark plugs should I be running.

I used to run NGK BR6SF I believe. Would these still work? Are they the correct length?

The Dart heads require a 3/4 reach thread , flat seat style spark plug. NGK R5671 A- 6

Dean Gellner

Are the plugs I have too short or in some other way the wrong size. Just courious since I have come a cross a few threads mentioning that the Dart heads require a longer plug.

I assume the R5671 A-6 is an NGK. Do you know of any other plugs for these heads just incase I can not locate the NGK's?

The shop that sold and installed the heads installed V-Power #9's. Are V-Powers the correct size? When I plug checked they seemed to read alittle hot.

Sorry for all the questions. I'm just very concerned about the possible problems with unknowingly running the wrong plugs. I did run the other plugs in a few cylinders to check my jetting. Sounds like I need to get them out.

Your current plugs are shorter. The NGK heat range chart goes from 1 being the hottest and 10 being the coldest. A #9 would be for a blower application. Are the engines Supercharged or N/A ?