I'm debating the value of one or both of these. My Conquest is down for a bunch of inspections and I'm thinking of doing these at the same time. My questions for the group:

Strakes - do you have real world experience with (i) yaw reduction; and (ii) performance increase? The performance increase would be very nice, but the main reason I'm wanting to do it is for yaw reduction.

Speedstacks - honestly, I'm just getting tired of the exhaust on the paint. I don't expect any performance increase at all. So, if they don't truly work to eliminate the soot on the paint, then I view them as a total waste of $15K. It's already a stretch, as I can buy a whole lot of washes for $15K. If they really do work, then I may do it for the cleanliness & preservation of paint.

Thanks in advance for input.

You are refering to a 425? I had speed stacks on a C90 and they do not eliminate the soot from the wing/nacelle. It is merely deposited on top of the wing instead of the side of the nacelle. Whether or not this is true in the 425, I have no knowledge...

Yes, 425. If all they do it move the soot around, this seems like a terrible use of $15K. Surprised that many people seem to have them.

On the C90 when you walk up to the airplane you don't see any soot. However, when you get to the top of the airstair door you see all the soot on top of the wing. This was a 1978 C90 that also had Raisbeck props and aft strakes. The airplane was 226kts true at 160-170 msl. I cannot attribute any extra speed due to the speed stacks. But, if you have to replace the stacks anyway (cracks?), why not?

Unfortunately we don't operate a Cessna 425 (great airplane) so I can't comment on how much soot is removed from the cowlings but one of our first customers did say there was a reduction in soot and it made the airplane easier to clean (more localized soot) He was also very pleased with the performance increase. Attached is what he had to say.
Best regards,
Jim Christy
VP Sales
American Aviation Inc.
800-423-0476