View Full Version : Greddy Profec Boost Controller HELP

08-04-2021, 11:56 AM
I have searched and have had no luck finding help. I have a Greddy Profec Electronic Boost Controller on my S13 Silvia. SR20DET, GT2871R turbo with supporting mods (fuel, intake, exhaust, etc.).

I have been having a hell of a time trying to get this thing tuned. I have gone through and replaced every gasket, seal, and hose that could cause a boost leak. The car boosts fine when running on wastegate only, but the turbo response is much slower than using the boost controller. But when trying to use the boost controller, seems like no matter what settings I have, it will boost to 9-10psi, drop down to 5psi or so, then start building boost up to my target boost. The initial turbo response is amazing, builds boost super fast, but then it almost acts like the boost controller is limiting the boost or opening the wastegate prematurely.

The turbo has the stock wastegate so it has a 1 bar spring and is only a couple years old and haven?t driven the car much since I?ve been troubleshooting it a lot and working on it.

Is anyone else using this boost controller and if so what are your setting?

My setting as of yesterday are:
Set: 20
Gain: 15
Start : 15
Warning: 20
Limiter: 20

Thanks for any help!

08-05-2021, 06:35 PM
Assuming it’s a Profec B Spec II, I believe the set is a percentage, try turning it up incrementally.

Turn the gain up incrementally as well after you set the initial percentage. Mine is set to 18%. Also you have your wastegate set to open at 15(psi?). If that’s where you want it then cool.

Your warning is where you want it to engage limiter IIRC, and the limit is what set percentage it’ll reduce to after them it hits the warn, so it should be lower than the warn.

My hi/low settings as follows:

Set: 28%
Gain: 18%
Set/gain: 0.85bar, about 12.5psi (when wastegate starts to open)
Warn: 1.2bar (about 18psi)
Limit: 10%

Set: 50%
Gain: 18%
Set/gain: 1.05bar
Warn: 1.4bar
Limit: 15%

These settings work for my particular build. The low settings are nice. Good response and caps out at about a bar of boost (15psi). Would not recommend my high settings unless your engine is built and tuned to handle it. Here is the manual:


Hope this helps.


08-10-2021, 10:58 AM
^^ good post

I just want to add some things

1. The vacuum line on the back of the controller is absolutely ESSENTIAL that it be a single, large, dedicated line that runs to the intake manifold. Do not T' it off to anything else and make sure the hose diameter is as large as the port on the back of the controller, and that this line is as short as possible.

2. This boost controller is an open loop controller, it has no feedback. It does not monitor your engine. It it not a PID controller, only P proportional gain as a duty cycle and amplitude output.

3. The solenoid greddy supplies is a 3-port solenoid generally capable of approx 50% duty cycle max usage. Anything over 50% duty on a typical 3-port will generally lead to poor control, oscillations or outright failure to respond.

4. How to use these controllers
A. Set the "start" function to zero so it does nothing
B. Set the duty cycle to 0% and gain to 10 or 15% so the controller is essentially "OFF"
B2. Make sure the warning is set higher than the max boost you intend to run so it doesn't trigger.
C. Now run the car at wot and see what your boost pressure is with the controller OFF. It should be nearly identical to when the controller is disconnected completely.

Now, begin turning up the duty cycle.
D. gradually increment duty cycle 10%, 15%, 20%, etc... until desired target boost is reached.

Now, fine tuning:
E. Begin turning up the "start" feature to delay the onset of wastegate cracking open. This will cause a "RUSH" to the target boost. It is OKAY to set the START boost higher than your target boost pressure. You may also wish to experiment with using more GAIN as it may further increase the rush and overshoot of boost target if desired.

For example, Lets say my duty cycle is 25% and my boost pressure is 15psi of boost.
If I set my "start" feature to 16psi, the boost pressure will Rapidly rise to 16psi (or slightly higher) then fall back to 15psi, giving the vehicle a sudden burst/onset of torque which may or may not be useful or desirable.

for a smoother onset of boost, set the "start" feature to a much lower boost pressure than your target so the gate can crack open sooner.