Offenhauser head spark plug length

justpassinthru

justpassinthru

Junior Member
I have seen a number of threads on this issue and it seems the popular plug choice is the NGK B6L plug. That plug has a 7/16" reach, which may be fine for stock heads. My Offy 8BA-425 heads measure 1/2" from the plug seat to the inside of the chamber, so wouldnt a spark plug with a 1/2" reach, such as the NGK B6HS be a better choice? Its still the same heat range, 14mm thread, non protuded tip, non resister as the NGK B6L.
Bill
 
I can't answer your question but I do have an Excel Spread Sheet/Matrix that gives all NGK plug numbers and all sorts of tech info for each pn, such as reach, etc. It also compares NGK to other well known plug manufactures and their plug numbers. I could email you a copy of this if you PM me your addy.

ps...one thing I failed to mention was I'm using the NGK B6L plugs in my Offy heads on my 59 engine. I chamfered a little material away inside the chamber at each threaded plug hole until the reach was right for the B6L's. Then I CC'd the chambers to make sure they were all the same. I'm not necessarily recommending that you do this but that's what several folks suggested that I do when I asked the same question. Maybe some of the engine building gurus here can comment more on this.
 
Last edited:
Don't know the exact measurements, but I've had good luck with Autolite 437's in my Offenhauser heads.
 
All flatheads with 14mm plugs were in the old days H10 why would we not use these. The champion replacement is H10C. They are available and I have some coming on Monday. They will be going into eddie meyer heads.
 
barnfind08 said:
All flatheads with 14mm plugs were in the old days H10 why would we not use these. The champion replacement is H10C. They are available and I have some coming on Monday. They will be going into eddie meyer heads.
Click to expand...

New Champion plugs have received a lot of bad press after they moved their manufacturing to Mexico.
 
Im not trying to figure out which spark plug manufacturer is better or not. That could be argued for ever. What I am interested in is the reach of the plug. The Champion H10C is a 7/16" reach plug with out a protruded tip. If that plug was to be used in a head with a 1/2" deep hole, the electrode of the plug would be up inside the hole quite a bit. I cant see how that will work good. The Autolite 437 is also a 7/16" reach plug but with a protruded tip. That may put the electrode where it shoud be, but would leave a pocket at the bottom of the plug which could cause firing problems? Not sure.
Bill
 
i had to champer out around the plug hole as the tips of plugs didnt go right through this was on a new set of edelbrocks:)
 
You must log in or register to reply here.
Back
Top