The 4 cylinder bikes are limited to 1,700ccs or 101ci. They rev to 14k. The twins go almost a liter bigger to over 2,600ccs or 160ci. They rev to 9,500. Their weights are within a few pounds of,p each other. Carbs or FI is allowed. BTW, are the Suk motors based on the liter motor or the Busa? They certainly look fairly equal on the track with the twins seeming to come on harder down track. And if there’s a top fuel Harley competition why not a top fuel in-line (ours) fours competition for example? Or truly unlimited, turbos, super chargers, whatever?