I disagree on this one- unless you are using a manual bc the most i have every pulled out was 2x the spring pressure -- this is because you can only hide no more that 50% of boost even at a 90% duty cycleStyleTegGSR on Feb/02/04 said:you can typicly go way more boost than the spring is made for, but the more and more you get the less reliable the boost is going to be
there is no set % of boost you can hide from any wastegate. its simply the more you go past the springs limits the less reliable it will begin to get. %50 is just a blanket number that people choose to use because in most cases you can go twice what the wastegate spring can allow. but also in most of those cases you can still go over twice. Ive seen people run 1.1bar on a .4 bar spring with a profec A. and it hit it every time. There are alot of things thast come into play with this, and really when dealing with forced induction a blanket number or statement, is not somthing you want to go by.95gsrturbo on Feb/03/04 said:I disagree on this one- unless you are using a manual bc the most i have every pulled out was 2x the spring pressure -- this is because you can only hide no more that 50% of boost even at a 90% duty cycle
Like TegGSR said, reading how boost controllers work, what makes 2x the spring the magic number?Lets start with the wastegate (WG). It has two parts. one is the actual flapper valve in the turbine housing for an internal gate, or the valve mounted to the O2 housing or manifold as an external gate. This gate swings (internal) or slides (external) open to allow exhaust gasses to bypass the turbine section of the turbo, so it cant contribute to building boost. on an internal, the bypassed gasses rejoin the regular exhaust gasses in the O2 housing, or can be dumped to atmosphere with an external dump O2 housing. With an external, the bypassed gasses almost always vent to atmosphere (loud) but can also be made to reconnect to the O2 housing.
The second part is the actuator. This is what actually operates the valve. It consists of a simple diaphram in a canister, attached to a rod that operates the flapper valve on an interal gate. on an external the diaphram is connected to the valve by a short rod that pulls the valve off its seat (much like a intake/exhaust valve in the head). There is a boost line connected to the WG actuator canister that allows boost pressure to push on the diaphram, which in turn moves the rod, and opens the valve. A spring pulls it closed. The boost level that the WG opens at is the same amount of pressure it takes to overcome spring pressure. So a WG with a 10 lb spring will need 10 psi to open the valve and limit boost. It acts as a closed loop control system for boost pressure.
The way a boost controller works is a pretty simple concept. But there are two types. First, the old style "bleeder" types. It just bleeds off some of the boost in that line so the WG doesnt see it, and stays closed allowing more boost to build. If we look at out 10 lb spring, and we "bleed" off 5 psi, we get 15 psi boost. The other type is "ball and spring." This type uses a spring loaded ball and seat valve to keep boost from ever reaching the WG actuator. once boost rises enough to lift the ball off the seat, pressure is allowed to rush in and open the WG. So tightening the screw puts more pressure on the spring, holding it closed tighter, requireing more boost to be able to blow past it and open the WG.
Electronic boost controllers like my profec do the same thing, but with Pulse Width Modulated solenoid valve.