i have spoken to various tuners around the world and have found the cheapest solution here in Australia. (some people im sure will see this a bad idea but it has proven itself on many occasions here in Australia with fast circuit, drag and rally cars)
Here it is- Use your bov as a boost controller.(bleed off excess airflow)
things you need*electronic boost controller or some form of control circuit to pulse a cycling solenoid and be able to adjust the duty cycle and the frequency.
*3 port boost control solenoid
*non-piston type Blow Off Valve (the stock one works best)
* an engine with a turbo which exhibits compressor surge under wot.
i'll explain the other advantages which i have found later in the post as there is some great benefits in using this setup even if there is no surge problems.
plumb your 3 port solenoid up in series not parrallel like the factory one but instead of sending the pressure to the wastegate send it to the actuation port of your bov. (the wastegate is not needed anymore but can be used as a safety feature, ill explain later)
the idea is to pulse the bov open and closed very fast in order to bleed of the excess air/boost which the engine is not using and allow the engine to only take the air which it can use.(the turbo is providing maximum flow constantly and the engine uses what it needs and the rest is vented out the bov)
the control circuit will pulse the bov at a certain duty cycle which will be different on every engine so some setup time is needed to ascertain the correct duty cycly which will relate to your desired boost level. the frequency is used to adjust the sensitivity and stability of the boost control.
positive points- allows small capacity engines to use turbos which are normally suited to larger displacement engines but use smaller turbine housings to aid the speed of spool up. The turbo is always producing its maximum airflow even though it may not be at its maximum boost pressure thereby avoiding superheating the air. with the high shaft rpm, during gearshift the turbo shaft etc still has enough rpm to be above the boost threshold so boost takes less than half the time to arrive when the throttle is opened again.(throttle response on gearshifts is phenominal). 3-4psi boost arrives 300rpm later,(some air is being bled away) but due to the turbo having less load on it during spool up it actually reaches max boost 400rpm earlier than electronically controlled wastegate. BOV still functions as normal on gearshift. induction roar scares the crap out of others.
negative points-although my map sensor reads a steady manifold pressure my pneumatic boost guage doesnt give a stable reading, instead what you get is a boost gauge where the needle flutters around the target boost level so fast it is a blur and the actual boost you get is exactly in the middle of this blur (maybe a different pressure source will dampen the fluttering). even though the guage is fluttering the car accelerates smoothly and if you couldnt see it on the guage you wouldnt know it was doing it. the ultra fast fluttering noise the bov makes while under boost may be annoying but people beside your car have the weirdest looks on their faces as the wooshing noises which come from under the bonnet are something that most people have never heard before.(i actually like it
) also shaft speeds are always high, if you have an IHI turbo i would not suggest you use this method as they are not as durable as a garrett or TD series mitsu turbo,(i dont think IHI make turbos which flow enough on the comp side anyway) my turbo is basically the same spec as an fp green but i have a to4e 57 trim comp wheel instead of the 50 trim, this made it a little "front heavy" which ultimately led to comp surge at pressures above 22psi.
the wastegate is not needed and may be completely disconnected, and while the bov bleeds the excess air away the wastegate will never open, however i set it to open 3psi above the target pressure so that it will open if there is a failure in the boost controller. i also set the electronic boost cut 2 psi above the wastegate setting. you will need to set up the wastegate setting with the bov control deactivated. i used the boost control feature in my Link ecu with a legacy rs 3 port solenoid instead of the factory wrx 2 port solenoid and my stock STI bov.
if using the stock wrx bov you will need to block the 3mm hole next to the valve to ensure it will hold more than 17psi. this does not work well with a piston type bov as the piston takes to long to change direction due to its mass. bad bov-blitz,turbosmart,turboxs,gfb
in fact the only aftermarket one which i think may work effectively is the greddy one.
if you have an air flow meter be sure to re-circulate the air before the turbo but after the afm.
food for thought.
if you have a big turbo, have a go and be amazed at the response which is now achieved.
Even launching is easier with the faster build-up of boost once load is placed of the engine.