Originally Posted by
zugig
That Denso plug is their heat range (HR) 20, which is equivalent to NGK heat range 6, which is stock for the 2013 VT but is way too hot.
XP5703 is equivalent to NGK HR7. I have used them with no issues, but others have reported breakage issues with them. XP5702 (HR8) & XP5701 (HR9) have thicker ground straps and are a bit more durable (have run both) but these are temporary/backup plugs at best.
You want a quality HR8 plug now and a HR9 plug as your tune gets fairly aggressive:
NGK R2556G-8 (recessed tip HR8) race plug is best.
HKS M40XL (projected tip HR8) is 2nd best.
NGK R2556G-9 & HKS M45XL for HR9 plugs (future reference).
Do not skimp on plugs. Pay for the better ones. Also, if you are over 40K miles on the original ignition coils, those need to be replaced as well.