JustJeff

iTrader: (13)

While I'm rebuilding my engine I'm also going to replace my converted N/A harness with another N/A harness in better shape. I paid a shop to do my turbo swap (JDM if it matters) so I'm learning and trying to replicate what they did 3 or 4 years ago.

My question is with my RB exhaust, custom intake and FCD I was going well over factory boost levels. IIRC the Duty Solenoid/Boost Pressure Control helped maintain factory boost levels. Once you were beyond factory boost that solenoid was no longer serving a purpose. Is that correct?

If that is correct can I simply depin 3R at the ECU and save myself from converting from 6 port to duty solenoid?

Once the engine is rebuilt I'll be going with an Rtek 1.7 and some sort of boost control, but I haven't decided what yet.

JustJeff

iTrader: (13)

Good morning bump

arghx

iTrader: (3)

On the left is the factory boost curve of a stock s5 T2. This is from Matsuda, "New Technology Employed in Latest 13B Rotary Engine," 1990. You can see that boost is supposed to peak at 60 kPA or 8.7psi by around 2500rpm, then taper off to 50 kPA or 7.25psi by 4000rpm.

The duty solenoid works just like most of the other factory electronic boost control systems out there (Evo, STi, etc). The solenoid is Tee'd off the wastegate pressure source. The ECU pulses the solenoid to bleed air away from the actuator so that boost can increase beyond the wastegate spring pressure. It's a perfectly good design that's been used for over 20 years by a lot of manufacturers. The FD does the same thing, it just has a slight plumbing difference.

The problem is that the boost control programming in an N370 or N374 based ECU is intended for a stock car with stock ports, stock intake, and most importantly stock exhaust. Changing those throws things off and could lead to excessively high boost levels if the factory duty solenoid is installed. It's designed for a peak of 8.7psi on a completely stock car but you don't know what it will actually reach without testing. It could be say 10psi (which may be exactly what you wanted) or it could spike way higher than that.

We don't have any way to adjust the duty cycle maps like you can on say an Evo or STi. On those cars you can reprogram the factory boost control system, which is why aftermarket boost controllers are less common for those platforms (especially STi). Now, if you had a Power FC or other standalone on your 7 you could control the factory s5 duty solenoid and use it for boost control, or you could swap in another solenoid and use the standalone with that. But that's a much bigger step in terms of cost and the amount of tuning required.

The safest thing to do is run a hose directly from the compressor housing to the wastegate and not run any boost controller at all until you determine what boost levels you are already going to reach. You may end up overwhelming the wastegate and overboosting even without any kind of boost control.

j9fd3s

iTrader: (3)

we actually did that once, on my friends FD we swapped in one of those big OBDII solenoids.

be careful though we were trying to get boost UP

JustJeff

iTrader: (13)

Very helpful response, thx

With the factory plumbing in place my boost was maxing out at around 12psi. While my rebuild is coming together I picked up Motorbooks Workshop's Turbocharging Performance Handbook to learn from.

My S5 turbo has too much endplay/thrust so I'm leaning towards rebuilding it myself and taking it to a turbo shop to be balanced. While that's happening I'm also leaning towards porting my wastegate. BUT I'm still learning and those plans might change.

JustJeff

iTrader: (13)

For the time being I'm not looking to add performance mods. Once I have my engine rebuilt and reliable I'll focus on "zoom-zoom."

Maslow's heirarchy of needs dictates that I should:
1) have the car moving
2) have the car reliable
3) etc
4) etc

j9fd3s

iTrader: (3)

i agree. if you wanna start slow i'd plug the port that ordinarily goes to the boost solenoid