If anybody needs “sonic nozzles” for their TSIO 550 intercooler installation, I have some.

I CNC machined the ones I used on my airplane and made a few extras.

The attached PDF file shows what the cross section of a “sonic nozzle” should look like.

Craig Berland

 

CWFMD,

 

I’d need more info to diagnose this completely, but write me directly and I’ll try to help.  rpastusek@htii.com

 

Some basics on the pressurization system (applies to the IV-P with Continental TSIO-550 engine ONLY--you didn’t specify the aircraft/engine):

The engine is designed to “vent” part of the turbocharger output overboard during normal operation, through what are called “sonic nozzles” that basically maintain a rather constant flow rate over a range of pressure differentials. The IV-P (and some other pressurized Lancairs with big bore Continentals) uses this bleed air to pressurize the cockpit. The air is routed through a mixer/control box mounted near the top center of the firewall in the engine compartment. This gold-colored aluminum can (about 2/3 the height of a quart oil can) has a cockpit-controlled shuttle valve that allows selection of a mix of hot air directly from the turbochargers and cooler air that has already passed through the intercoolers.  It also has a separate valve, with cockpit control, that shuts off airflow to the cabin and diverts it out the bottom of the engine compartment when cockpit pressurization (and associated heat) is not needed.

 

As to heat, at full throttle, the turbocharger output air temperature can be up to 300 degrees, and in the cabin heat on mode, flows pretty directly into the cabin. With the heat control turned off, the turbocharger air passes through a pair of air-to-air intercoolers before heading to the cockpit for pressurization. The problem is that these intercoolers only lower the temperature; they don’t deliver “cold” air out the backside. When the input is at 300, the output is warm, at best; hot in Texas in the summer. So, without air conditioning, there is not a good source of really cool air available to pressurize the cockpit.

 

As to the fixes: First check is to be sure the valves in the controller are functioning as intended.  Second check is to be sure you have sonic ports installed in your turbocharger output lines that feed to this controller. The variation you report in MP would tend to indicate there are no sonic ports installed, and that you’re getting “full flow” through the system, rather than restricted flow as intended…but this is just a guess at this point… not enough data. Talk or write?

 

Bob