Been running NGK-9 (R5671-9) in my 15-1, Indy -1 heads, flat top piston, 57cc chamber. Renegade Pro 114 fuel 7200 rpm max. Any advantage to running the projected tip? Also not really sure if it needs -9 or-8. I have both -8 extended (R5672-8) and normal tip (R5672-8) in stock. I'd have to get more -9's
Thanks Doug

Do you have room for the projected tip plug? As for heat range what does the plug look like? I have run -8's at 15-1. But it is combination dependent whether it can be tolerated or not.

It has room as the piston is a flat top, zero deck, .060" gasket. The 9's were fine. But I only have -8"s in stock. If i have to get -9"s then which ones? extended or normal?
Doug

I always work my way down form 10-9-8. Just my method and depends on timing and what fuel.

I would try them both and run the ones that worked the best for your deal

Every flat top motor I have ever had ran a little quicker with the projected.

If you have the room, and it appears you do I would go with the extended tip.

Doug, i have run -9 exclusively in 15.25 compression motors, 5672-9 in both 550 with indy 440-1 heads, and 572-13 heads. The 572-13 combo has a dome that requires indexing the ground strap between 10 and 2 oclock. I have no problem getting good readings off the plugs running methanol. Those combos made 926 hp and 982hp respectively.

FWIW...I ran NGK R5671A-8 (4554) plugs in my 14.5:1 dome piston Indy SR headed 446" wedge w/ no issues. Ran on Renegade 112 fuel.

NO projected tips for nitrous use ........

I installed the R5671-8. Ordered a set of R5672-9
Doug

My new B1 motor came out to 14.3 CR since I bought the 0.056" Cometic head gaskets before the block was decked (0.020" piston below deck).
Almost a flat top piston, just a 0.091 " flat dome.

I started running the motor with R5671-9, it was fine. Looked like it could tolerate hotter, so i put in R5672-8.
Running methanol, they look clean and no issues. I think either will work, just the -9 will not last as long (fouling).