How do the Merlin wastegates work?

I understand wastegates and turbo systems in general. I'm wonder specifically how the merlyns are setup on the seneca. Is there a seperate wastegate controller, a link rod to the throttle, or ??? In other words what causes the wastegate to control boost, and how does the pilot affect that?

https://www.merlynproducts.com/awholenewairplane.pdf

You should also get intercoolers to get the most life from the engines. To get the most performance from the plane, you'll want to use altitudes in the 11,000 to 18,000 foot range. Intercoolers will help the cylinders live longer.

http://turboplus.com/

The Merlyn system for Mooneys and Sennecas holds a constant pressure in the "upper deck" (i.e. upstream of the throttle) as long as the turbo can deliver that much pressure and the MAP is set directly by the throttle.

The Merlyn is a differential controller, it has a reference on either side of the throttle body and aims for a constant pressure drop(approx 4").

When I bought the M20K, the PO didn't have any of the STC paperwork or even a 337 for the install. Merlyn was great to deal with and charged a minimal fee for the STC package.

Ahh, ok. So I assume if you ram the throttle all the way open at low altitude you can overboost it then, correct?

Yes, you can in the Seneca II/III (and Arrows, Mooneis and many other aircraft with TSIO360, except for the TSIO360-RB engine, in the Seneca V which is very different and modern) There are over-boost valves on the engine that relieve the overboost so you don't damage the engine.

Normal take off at sea level in the Seneca II/III is about 3/4 throttle, not wide open. You, Mr. Discount Seneca Pilot Guy, have to advance the throttles until take off power is reached, and stop advancing the throttle at that point. At higher altitudes, the throttles need to be opened more. But you read the MP gauge to set takeoff power.

Like I said, you get used to operating them, ain't that big of a deal.

The Merlyn is a simple device, and it improves efficiency, by reducing the amount of turbocharging when you operating at reduced MAP, and also can improve critical altitude.

Ahh, ok. So I assume if you ram the throttle all the way open at low altitude you can overboost it then, correct?

I owned / operated a Seneca II for a number of years. Mine had the Merlyn's, Intercoolers and a number of the Lopresti mods (cowls, etc). Overall it was a nice machine and great for family trips. We could stuff alarge SUV completely full and everything easily fit in the Seneca. I think it's much more practical as a 4 seater by removing the middle row of seats, which frees up a ton of space for luggage, etc. It's not at all a comfortable 6 seater. The Merlyn's make managing the turbos much easier and I'd personally recommend them.

The main issues I had with our Seneca was the lousy autopilot I had (Century) and I'd certainly want a more modern autopilot if I flew one again. The other issue I frequently had and I understand is common among many Senecas is exhaust leaks. The interface between the exhaust manifold and engine seems to develop small leaks which, over time, reduces the ability to make MP at altitude. The mechanic who was working on it found a tool that allowed him to refinish the engine block interface without pulling the engine.

Yeah, the autopilot in mine was a sore point for a long time. It was an Altimatic IIIC (Century 3). However, once I got it entirely working correctly, and added GNSS steering module, it was actually pretty good. Mine had all the options, with glideslope coupling.

It had the common problems in the IIIc series, namely all the "blue" connectors throughout the entire AP wiring harness, and a bunch of completely stupid hacks into the harness when avionics were changed over the history of the airplane. Thing is, none of those cuts and hacks into the AP harness were ever necessary. Once all those were replaced and the attitude gyro rebuilt twice, and all the servos overhauled, it was actually quite good.

When I sold and got the Columbia 400, the Garmin G1000/GFC700 are in a completely different class of autopilot.

Now you can get a GFC500 for your Seneca, if you want to spend the $$.