why is that they miss without the extended tip plugs?

Because the non ext-tip doesnt burn as well with alky causing a slight miss.

wonder if the 3910's plugs would fit my engine? steel 990's with big dome piston to get some compression. present plugs are autolite 145's, have gapped them from .018" to .035" without success. big difference in reach between the two plugs.. :?:

I also run Autolite 3923 in my small blk. they are exteded tip, don't know if they will work with a b/blk, i have to index them with my 14 to 1 pistons, just a suggestion.

Zip.

thanks for the tip, Zip! i have some leads to follow up on...won't get out again this year. it's a long off season up North :wink:

Also a decent ext tip plug, last sunday a guy at the tracks with 565 18 degree big duke engine had a slight miss they'd been looking for. I looked it over for them, and tested a few things but I kept going back to the 3923 although a ext tip, still do have a miss issue in certain combos do to the difference in the stap on the plugs. I found a set of plugs, replaced them and he went on to 2 finals that day, miss free. Although big dukes are a different animal, I feel the strap on the 3923 can cause a issue vs the 3910, on certain combos. If I get some time, I'll shot a few pics to show the difference.

I'd index them and roll the engine over by hand and see if they hit, if not id give them a try.

thanks David, pics would be great!

the standard plug reach is .460" and is flush with the chamber. do i need to get the tip into the combustion chamber as far as possible? change up to .750" reach and extended tip if it will fit?

which way do i index the ground strap? did that many many years ago with a small block dodge, made no difference in that instance.

Wooh !!, you can't use a .750 reach plug if you are inside the chamber @ .460, but you can still use and extended tip plug, but a short reach. This now becomes a whole new ball game. I don't personally have any heads that use the short reach heads, so i'll leave it to someone who does.

Zip.

I also do not have a head that uses a short reach, mine are all good with the ext tip. Like zip said you can not use the long reach plug, but will need a ext tip, and at that point my knowledge runs out with the plugs as I do not know which plug to suggest.

OK, just the extended tip if they will fit?