My 421 is pretty close to book maybe slightly better. The guy I bought it from took everything he could off the exterior and cleaned it up.

I flew yesterday at almost max gross and it was slower for sure. so weight does matter. I think I was down 10 knots from what I see when lighter.

With full tanks and just me it gets over 220 at 65% power in the flight levels So I don't see why it won't hit the book numbers with more power and or higher.

would I call a 421 a 240 knot plane, no. Its more of a 220-225 knot plane at 40 gph.

Mike

We operate seven C421Cs and have accumulated about 7,000 hours of experience over the last 15 years. We operate at 1800 RPM (for sound level) and 32.5" at all altitudes. That is about 73% power. Obviously, the highest TAS will be at FL250. We routinely see 220 TAS at 250 with 23 GPH. CHTs are comfortable at 300 - 350.

The engines are rated at full continuous power and the RAM modifications have remarked the MP gauge with a green arc up to 35". I can see someone operating at 35" (because of the revised green arc) and 1900 RPM (with noise cancelling headsets). At that point I can see 235 TAS, but why do that? Airspeed goes up with the square root of power increase while fuel flow goes up linearly with power increase. That extra speed will have a high cost, shorter range, and higher CHTs.

Also, these engines are considered somewhat fragile. We normally can get all the way to the 1600 TBO with an occasional cylinder replacement.