Interesting. So you are aware 20lbs isn't right. An apex engine should weigh roughly 8 pounds more than a nytro engine. So, there is 66 pounds extra in the chassis and apex specific components. Extra fuel is a big contribution. How many extra gallons in the impulse tank setup? 2 gallons including the surge tank? A new sidewinder is roughly 640 pounds rtr, so that is doing pretty good considering where an impulse apex would start. Scott may have reduced the wall thickness on the nytro chassis to cut weight too. Have you compared tubing wall thickness?
I was told the engines were 18 lbs difference between the two. Looks like I was misinformed from doing a little digging online. 6 lb difference seems to be bare long blocks, I was figuring the 18 lbs plus an extra throttle body, wider intercooler, 4th header tube etc. to come to what I thought was a 20+ lbs difference between the two setups as they sit in the sleds.
I havent had to do any modifications to the nytro tubing, I dont think the wall thickness is any less on the nytro but cant say for sure. I had to do a fair amount of work to my apex chassis and the wall thickness is thin, ill measure it when I get back to my shop.
All I can say at this point is the steering is WAY more complicated on the apex, the post goes down, right to the chaincase, forward, left, then down. Everything in it is heavy steel, with thick bellcrank ends, pillowblocks, etc. That is the biggest advantage the nytro has with its more rider forward steering setup, the post goes over the engine, straight down to a small tie rod then to the bellcranks.
The nytro also has stock sideplates which I would think are heavy but apparently not? On the NYPEX setup scott used custom cut sideplates then apex chaincase, and drive/jack shafts which finally allowed a drop and roll on a nytro chassis. The nytro titanium front clip has a lot going on and I would have thought it would be fairly heavy comparted to a somewhat simple apex bulkhead.
The impulse fuel system according to paul is 12 gallons in total fuel capacity (cell and surge tank)
The nytro has an xp fuel tank which is rated at 10 gallons.
Both sleds have big double pass U coolers also.