Hey guys I picked up a gen 5 Turbosmart wastegate as a Christmas present to myself. The gate is supposed to have the 14 psi spring installed but looking in the box it's still sitting in there and the 5 and 7 psi springs are installed. Is it a better idea to run a slightly lighter spring (12 psi) and more controller vs a heavier spring (14 psi) and less controller?? Turbo is a TNT 88/96 T6 with the gate inline just before the flange. I'm not running Co2 or on board air it's plumbed from the compressor into the bottom port of the gate and into the dual mac valves and controlled by the Dominator ECU. Thanks guys

 

depends on target final max boost and exhaust gas pressure
With a typical controller that has full pressure plumbed to the bottom port and controller solenoid limiting on the top port of the gate with a 3-port solenoid
A 12psi spring should be able to make about 18 to 20psi of boost before having some trouble turning up higher
I've taken a 3psi spring to about 12psi before using this setup before it had difficulty
I've taken a 10psi spring to 18psi before having some difficulty

The exchange rate is not linear, and also depends on exhaust gas pressure and controller frequency vs the response of the solenoid to that frequency
There are other configurations such as 4-port and other ways to plumb the gate to squeeze more controller out of them but I find that control becomes more 'touchy' and has a much more narrow range of settings
whereas the traditional 3-port limiting the top of the gate has a very wide range of adjustment
This is important for changing climates when using open loop boost control, the open loop does not adjust for changing climates, so when the the weather gets cold its typical to see more boost pressure. The increase will be much higher with one of the non-traditional(4port) control methods because of the limited range of adjustment over which changes seem to occur in terms of boost vs duty cycle.

In short I would try to keep the spring close enough to your final expected target boost but also low enough that you can turn the boost down for diagnostics and lower octane fuel and hot climate conditions as needed.

 

I run a dual 3 port mac valve setup with a dome pressure sensor in the top of the gate. The current gate has roughly 14 psi spring and target boost is 25 psi which it hits no problem. I've just never really given any thought to lighter vs heavier spring and more or less controller

 

Its usually feasible to roughly double a spring worth of boost pressure using that setup. But there is non-linearity with exhaust gas pressure vs gain of signal depending on controller options. With something like a haltech or other stand-alones you adjust duty cycle per rpm breakpoint but with hand held controllers like a greddy its not always simple to maintain a set same pressure to redline when pushing the limit of a spring
with a 14psi spring and 2:1 EGP i would expect some difficulty getting much past 28 or 29psi with the 3-port traditional

 

I do run a back pressure sensor in the turbine housing but it needs a canister to smooth out those readings and I'm also considering picking up a Motion Raceworks CO2 setup since I've got no back seats I'll mount the bottle beside the fire extinguisher

 

Whatever min boost you plan to run should be the spring and run a co2 system for more accurate control. Thats the best way assuming controller isnt limited with how much you can supply. If you have to use manifold pressure for source then yeah run more spring closer to your desired boost.

 

Copy that! I'm on a Holley Dominator ECU with its boost controller. Right now I've got things working great on compressor source but I've been looking into CO2 control for faster response. Motion Raceworks makes a nice kit that would take a few minutes to install them and would just be figuring out the PID settings for the fixed pressure source. I have no problem hitting my target of 25 psi right now on compressor

 

You should bench test the gate to see what PSI it actually opens at. Generally I run the lowest spring I can and with an EBC or MBC to achieve my target boost. That way if the controller fails you will default to a low boost. Usually you can about double the gate pressure with a EBC/MBC so a 12psi spring should be good for 24lbs at 100% Duty but that depends on gate priority, pre turbine BP and the size of the gate.