This is what I am using. Just put on the smaller pulley and going for 16 to 18 psi.

NGK 4554 - R5671A8 RACING PLUGS

Can be found @ your local parts store. Stocking number is 4554.
Gap comes set @ .28 and you will need to remove a little fuel down low.

 

I ordered the 4554 plugs which are TR8 if we want to use that naming. I noticed that there are two tops for the plugs even if they are the same heat range.... One has projected nose and the other doesnt. I think for high boost application non projected nose is better while the projected nose has better idle characteristics. The TR8's which is 4554 will always be non projected nose, but the TR7 has two different part numbers because of the different nose on them.

 

This is the exact reason why I had to pull 2% to 4 % of fuel in some spots.

 

The "reach" on a 4554 is 0.750". The "reach" on a factory plug is 0.708".

You can get a "TR8" heat range in a 0.708" reach which is also a racing plug. #7317 or R5724-8. May not matter.

 

There is a projected nose version of the 4554 also, but I don't know the part number off hand... I run the 4091 (racing non-projected nose "TR7", p/n R5671A7) in my LT1 turbo setup with Trickflow heads.

Both the 4554 and 4091 are .750" reach gasket seat plugs. The Trickflow LT1 heads call for that, so I don't have any issues with the added reach or gasket instead of tapered seat... For anyone running heads wanting the stock .708" reach, check your clearance first (shouldn't be a problem in any low-compression build-up).

 

all the info you could possibly need:

http://ngksparkplugs.com/images/pdfs/product_list.pdf

http://ngksparkplugs.com/images/pdfs/racing_catalog.pdf

 

I run TR6 with 19 psi on 93 octane.

 

TR6 here ~17 psi

 

From my experience I have ran everything from TR6s to AR3934s (-8 NGK heat range) both tapered and gasket seat, Darts can use either, and never seen one bit of detonation or fouling. Its pretty simple really, just keep going colder until you start fouling plugs or missfiring. With the a/f at 14.7:1 at idle and part throttle I doubt you will foul a -8 heat range plug drving around but if you run the car rich at WOT with too cold of plug you may start getting missfire issues. With the stock PCM I couldnt use -8 NGK plugs, it would missfire badly at high rpm, with the BS3 I can so its best to experiment a little.

Its not like TR6s are a 'hot' plug by any means, thats why a lot of guys still use them.

 

YEP! I run a lean cruise of 15 to 16.1 Drives fine. Im still fine tuning on the idle. Seems the cold weather has an effect on my idle.