392x autolite plug question

[blksn955.o]

I have been messing with plugs here and there over the last 3-4 years and finaly think I may have found the correct plug to run. From searches people seem to run the 3924-3925 plugs on gt40 iron heads and other aftermarket heads. I bought a set of 3923's as I need a colder plug with the higher compression and bottle. My question is do all 392x plugs have the high ridge at the end of the threads by the taper?? Should I have looked for a diff. plug (remember I need to run the colder plug). I ground down the ridge flush with the plug body, being carefull not to damage the threads or plug itself as the ridge would not allow the plug to fit. I am not having an issue with loss of comp. from what I can tell. This has just been in the back of my mind and thought I should ask.

Thanks

 

[2L8ULUZ2]

The GT-40 iron heads do not use a 3924 plug or any variation of heat range on that plug. They use the autolite 764. There is a reason that they will not fit. The 764 plug is a taper seat plug like the stock autolite 24-25 plugs but it's a little longer. The 3924-3924 is a gasket seat plug and that is why it is not working for you. Go get you a set of 764's and they will work just fine and are the same heat range as the 3924's.

 

[blksn955.o]

Thanks, what is the cold plug to run (1-2 at least colder), 763-762 right? Every time I go to the autozone they give me plat. or dont understand why I need a clolder plug and end up going round and round.

I saw a guy who was running 3908 in a gt40 headed car, had over 250hp n2o though, threads are the same on the 3923's as the others I have run (one set was the 764's). They are working once I ground down the raised end.

 

[2L8ULUZ2]

The stock heat range is a 765. One colder is a 764 and two colder is a 763.

 

[blksn955.o]

JEBUS H CRIST

went to check on the 765's the guy goes and they dont have them and cannot order them at autozone, I then go to advanced and look for them or the NGK plugs. He goes to look for the 765's and finds that the next step colder plug is a totaly diff. number system plug. So he looks for the NGK and get the tr55-or whatever- but again the next coldest plug he has around is a diff. number and has way diff. threads/length.

I then go to a performance shop and they direct me to the local shop they order from. I go there and as he is looking at the book sees H.O. says well I would think the cobra would be the H.O. and I said well all the mustangs are H.O. and have roller motors and before I could even say they have the 351 fire order that makes them the H.O. he starts giving me a lecture about how that does not mean anything and goes on to insult me and call me dumb like his "stepson". So anyway he is going threw his NGK book and I get the funny fealing he is x ref. the e7 plug as I keep hearing the urxxxx instead of the tr or t as I know the gt40 heads use some kind of tr55 and I say this. So he then goes to the BIG rack and I notice the autolite number and point that out and say there that is the stock plug and that is the vin number I need you to look up. He goes to the counter and sees the tr55s and x ref. the tr6 plug.

I am now realy pissed again (everytime I have looked for plugs I keep getting this crap), and I got the NGK hotline number and called them to make sure the guy was not getting pissed at me and giving me some BS plug to get me out the door. It looks like I finaly have the correct plug in the TR6.

GOWD DAM this is why I have now had like 6 diff. sets of plugs in this car. For the love of god you say you need 1-2 ranges colder and no one knows how or were to look.

Thanks for the help 2l8. I just wish it was that easy to get the correct plug the first time here.