I see only two options in your situation: The current Cat engine in the Challenger or the Sisu in the MF. Obviously both combines will be the same other than the engine difference as far as performance is concerned. You have been well advised by both of your trusted friends that the Cummins is not the way to go. As far as which engine is better between the Cat versus the Sisu, I don't think anyone will or can dispute the strength of the Cat engines, and the C9 seems to be one tough engine. As for the Sisu, I know they too have a good reputation. There will, of course, be a learning curve for many of the AGCO dealers to be trained on them, whereas Cat dealers will be very well prepared. The Sisu will be a great improvement over the Cummins, I am sure, but stating at this point that it is better than a Cat would be a stretch to say the least. It has to prove itself in the combine first; tractor engines and combine engines have different requirements. I would have to disagree with the post recommending the MF dealer on the basis of their competence with ag customers. If I assume by your name that you are from MN, then your Cat dealer would be Ziegler, and their service is superb, not that the MF dealer's isn't. But don't discount the many capabilities Cat dealers have over most other ag shops. Factors you should weigh include competence of personnel at both locations, parts availability, what happens if you need a loaner combine, and so forth. Whatever brand you choose, the base combine is a fine machine.
