So I got a bunch of NGK FR45's for my BBO with HEI in the mail.

They're much longer than the known-to-fit AC Delco R46SZ's, I'm using now.

I'm concerned the NGK's will hit the piston. I'd like avoid piston damage. Overall height is the same, but the head threads run waaay deeper on the NGK's making me think they'll protrude waaay too deep into the cylinder. And maybe kiss a piston (goodbye...)

Look at the comparative length vs. the Delco's...

Is anybody the NGK FR45's with big block olds 400, 425 or 455 with stock heads?

I just don't know how "tall" or "deep" the stock B head is, i.e. whether it can accommodate the seemingly longer NGK's.

Thanks in advance.

cf

 

Those are the wrong spark plugs, do not use them! You should have used the NGK XR45 or XR5 plugs

 

don't use those FR45's

you put those long plugs in your bound to break parts.

 

Many thanks for your views and alternative parts number citations.

They sure didn't look right to me, but I was wondering if I was just uninformed.