I’ve become a huge fan of using a manual boost controller (MBC) in parallel with a 3-port boost control solenoid (BCS), as described by ride5000 in this NASIOC thread:
There’s a good diagram here: http://forums.nasioc.com/forums/showpost.php?p=26050314&postcount=174
If the diagram is confusing, maybe text will help:
- The boost source (the fitting on the compressor outlet) goes to a tee fitting.
- One leg of the tee goes to the manual boost controller’s input.
- One leg of the tee goes to the boost control solenoid’s input.
- The outputs of the MBC and BCS come together at another tee.
- That tee connects to the wastegate actuator.
Whichever controller (manual or electronic) opens first ends up controlling the pressure to the wastegate actuator. So if your MBC is screwed in for 50psi, but the BCS opens at 20psi, then the BCS wins and you get 20psi. Or if your MBC is set to 15psi and your WGDC is at 100%, then MBC wins and you get 15psi.
- Nothing will give faster boost onset than an MBC. It just stays closed until you hit target boost.
- The BCS solves the part-throttle-full-boost problem, which is annoying when using an MBC alone.
- The boost control table can be very simple (see below).
- You can pick your boost level by turning a knob…
- …which allows you to hit your chosen fueling/timing every time
Setup is just sooooo much easier than tuning boost the old-fashioned way. You just need a WGDC table that looks about like this:
There are basically just two variables… well maybe three:
- At what throttle percentage should WGDC be zero? I used the throttle opening where boost starts building.
- What’s the WGDC you should have at 100% throttle? This is your protection against over-boosting in case you accidentally screw in the MBC too far by accident.
- You might want to adjust the shape of the curve between those two points. You might not.
In theory it might make sense to shape the table differently at different RPM, but the table above just works so well that I haven’t bothered. It drives very predictably.
Once the WGDC table is set up, you can turn the MBC all the way down to tune your fueling and timing for wastegate boost. Then turn up the MBC gradually and tune everything from wastegate to full boost with whatever boost level you want.
Turn down the MBC for a simple valet mode, or for a sunny track day if you’re worried about overheating, or to hit fueling/timing cells that need extra attention. Then just turn it back up when you want to go back to normal. It just doesn’t get simpler.
I use a Hallman Pro RX manual boost controller. I’ve heard complaints about some others, but none about those one. There are tons of 3-port solenoids on the market, most of them are made by the same 2 or 3 manufacturers, and far as I know they all work equally well.