What engine family is the 400 EXC from?


What engine family is the 400 EXC from? I’m asking if I can take the crank and/or cylinder and head from a different bike and make it bigger.

Sunny Adams:

All RFS motors have the same cases. From 250 up to 570. The differences are in the crank and bore sizes. By mixing and matching you can build all different kinds of configurations. The 400 has a short stroke crank. For instance, you can build a short stroke 450 or a long stroke 450 by using different cranks and piston diameters. Or use the stroker crank and a 540 kit to build the 570 monster! I own a 400 exc and it is an absolute sweetheart of a bike. I love the way it buzzes down the trail. I actually own a 400, a 450 and a 525 all RFS’s, all awesome.

Derek 6 years 12 Answers 1221 views 0

Answers ( 12 )

  1. Stop creeping Danny Ray Sanders

  2. Yep RFS, tons of combos you can build from that

  3. I think there was a newer 400 a few years ago. It was not a RFS. What vintage are you asking about?

  4. A better question is do the 400 and the biggest RFS share the same cases

  5. The 400 has a longer stroke.. why they did this I dont know.. torque perhaps

  6. Is the 525 the same

  7. Simpler question. Are the cases the same

  8. If the cases are the same on all Rfs, then 610cc is possible with all KTM parts. Or 640cc+ with some custom piston and jug options. Love my 600 monster.

  9. The old 400sx was a sweet engine. Much better than the EXCs, in my opinion.

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