I have a friend who was fortunate enough to participate in some of the engineering of this engine. I don't THINK this is a repost but let me know if it is and I will just delete it. It has a lot of cool ideas in it. I love the engineering that goes into stuff like this to deal with restrictions placed by sanctioning bodies. Most of this is cut and paste out of the email he sent it to me in.
-550 hp through two 34mm (last I knew...) restrictors
-180 degree firing duration, two cylinders fire at a time instead of 1 every 90 degrees like we are used to. The crank looks like a four cylinder crank. That's what give those engines the super deep and thunderous exhaust note
-1 7/8" primaries and a tri-Y long tube header, this along with the firing order make for awesome scavenging.
-It has a 4.1xx bore and a 3.1-3.3" stroke crank which make it super efficient and fast rev'ing.
-Each runner has its own throttle blade, the entire air induction system is carbon fiber.
-The plenums are above the heads and you can only see about 1/4 of them on the engine, they are massive!
-The engine sits 2-3" lower in the chassis and the top clearance is for the huge intake sys.
-Highly modified cylinder heads, you can see the plugs for the water jacket, they are used to seal off the provisions for the water jacket core printing which allows for a super precise casting.
-All structural castings are low pressure cast and cost 3-4 times more than a typical casting.
-belt driven cam drive
When I first saw the pic I immediately noticed how different the block looked but couldn't place exactly why. He explained to me that "the skirt that hangs below the crank CL has been machined off and a cast girdle that doubles as the dry sump pan has been fitted to cap the bottom of the engine. Add 1" to the skirt on an oem block and that'll give you an idea of how compact that engine is."
Very cool stuff, IMHO.