MXA TEAM TESTED: TWISTED DEVELOPMENT 450SXF EXHAUST FLANGE

WHAT IS IT? In order for a four-stroke engine to work at the highest levels, each part of the combustion and exhaust cycles must be perfectly matched. The fuel/air mixture must be unobstructed on its way down the intake tract. The camshaft must lift the valves, not only the correct amount, but for the proper duration for the desired powerband, and the exhaust valves must open at the correct number of degrees to ensure that any pressure left in the cylinder is efficiently blown out of the exhaust port. The art of making usable power requires a delicate balance between pressurizing burnt fuel to push the piston down and then opening the exhaust valve at the exact right moment to avoid pumping losses. How each element is configured is a matter of serial compromises, but one thing you can’t compromise on is the shape and free-flowing design of the ports—starting at the intake port and ending at the exhaust port–which is exactly where Twisted Development’s KTM 450SXF exhaust flange comes into play.

WHAT’S IT COST? $249.95.

CONTACT? www.td-racing.com or (951) 698-7222.

WHAT STANDS OUT? Here’s a list of things that stand out with Twisted Development’s KTM 450SXF exhaust flange.

The Twisted Development exhaust flange (left) is matched to the shape of the exhaust port. The stock exhaust flange (right) is round.

(1) Concept. Believe it or not, for all their genius at building the KTM 450SXF engine, KTM’s engineers dropped the ball on the exhaust port. The aluminum port and steel flange do not line up perfectly. In short, they are not matched. There is a lip where the two parts come together that disrupts exhaust gas flow. Twisted’s Jamie Ellis built a bunch of differently shaped exhaust flanges until he came up with a design that allowed the exhaust pressure wave to enter the exhaust pipe sans turbulence.

(2) Throttle response. Many KTM 450SXF racers want the low-to-mid transitional power to pick up quicker and feel more responsive from the get-go. And, that is exactly what Jamie’s flange did. MXA tested it with the stock KTM exhaust system, and it didn’t require any mapping changes. Every MXA test rider reported a noticeable increase in power off idle and revability. When you add quicker revs to increased throttle response from low to mid, it not only enhances that part of the powerband, it has a carryover effect from the mid on up.

(3) Installation. The Twisted exhaust flange is easy to install. There are only two bolts holding it onto the cylinder, and the exhaust gasket can be reused in most cases.

WHAT’S THE SQUAWK? MXA has Vet test riders who believe that KTM’s super-manageable low-to-mid power delivery makes the 450SXF easier to ride. We took special care to test with riders who thought the KTM’s low-end throttle response was perfect as is. Surprise! They didn’t want to spend $250 to change what they liked. In the end, they liked what the Twisted Development exhaust flange did, but they still didn’t want to spend $250.

MXA RATING: If you’re looking for more snap, quicker rev and improved pulling power from your KTM 450SXF, the Twisted Development exhaust flange will be your cup of tea.