Has Anyone put a IO-540 260 into a MX7-235? If so, what are the pros and cons. Is more power worth the extra weight, fuel and speed. I plan on using this A/C for float operations only.

Strange place to put this, but you need to call a guy named David Wright in Moultrie Ga. 229-343-3163

msanger, the extra weight and fuel burn is not worth the extra horsepower unless you are operating from high altitude lakes ie 3500msl and up.
Floats are high drag items and the extra speed you get from the 260 at altitude does not correlate with the extra fuel burned and thus less range or more load to carry.
Jeremy

Jeremy,
At altitude is there any difference in power between a 235 and a 260?

Yes. As you know, horsepower gets used up as altitude increases so there is a little residual with 260 when the 235 poops out, but the wing and prop has a lot to do with the final performance. At sea level, same gross weight, same prop, same tyres (drag and angle of incidence to ground), you can hardly measure a takeoff roll difference.
Not much difference at 2500ft, but as the takeoff altitude gets higher, say 3500ft msl, you can see the difference. Best cruise on the 235 is 7500ft whereas it seems best at 8500 on the 260.
The 260 is about 12lbs heavier and if you use the same % of total hp then the 260 will use more fuel and because it can go a tad faster it produces more drag so fuel consumption is up and range is down.
These engines could all do better if Maule did not neck down the exhaust flow at cylinder outlet.

I was thinking that if the RPM was the same, then the HP would be real close. I'm not sure if the 260 has a 5 min. limit for T/O or not. If it did or if the RPM were brought back to close to 2400, then I would expect the horsepower difference to narrow quite a lot.
Oh and on mine now that it has the VG's it trues out fastest between 9 to 11 thousand at 2300 RPM and loaded about to gross. It used to true out at about the same speed, but two thousand feet lower. For whatever thats worth.

The 260 IO540 has 300rpm more than the 235 IO540W and O540J at 2400rpm, but also a little compression difference though not as much as the O540B at 2575rpm .
Jeremy

Thanks for your input.