The 1200 motor is heavy , I bet a ACE 1200 would be lighter
As it is the 900 ace is only 22 pounds lighter than the 1200 and that is in the XS chassis.
600 Ace Sport - 454 lbs
900 Ace TNT - 485 lbs
1200 TNT - 507
unfortunately they don't offer the 600Ace and 900Ace in the exact same platform so you don't know exactly how much the extra 300CC cylinder added in weight but I think the TNT is usually about the same weight if not less than the sport. So using that logic the 1200Ace TNT at only 120hp will be heavier than the 1200 TNT and that is in the XR chassis. Seems like the Ace engine is not as light as some thought as it gets bigger.