If I went with a Drag Gen 3 kit, the turbo itself is capable of at least 18-20 lbs. of boost right? So to control the boost level a wastegate determines this right? Now, if I want to boost 6-7 lbs. now and 12-15 in the future what kind of external wastegate would I go with? I was reading about Tial wastgates and some mentioned different springs which is what prompted this question. If anything is vague let me know and I'll try to clarify. TIA.

 

wastegate determines lowest possible boost level (wastegate with 7psi spring in)
This is will be the max it will hit, UNLESS you use a boost controller which will raise the boost to anything you want. However the boost controller can NOT lower the boost to anything lower then the wastegate.

 

so how does the boost controller override the wastegate spring then?

 

A wastegate spring that is (X)psi dumps excess exhaust gases when the wastegate sees X psi.

A boost controller, no matter how expensive or cheap, is just a bleeder valve that bleeds off pressure so that the wastegate doesn't see X psi until the boost controller allows it.

I.E.
when your Manifold Pressure reaches X so does your wastegate and it dumps.

If you have a boost controller your manifold must reach X+Y psi, before your wastegate will dump.
That +Y is however much manifold pressure your Boost Controller is bleeding off.

M.P. = 6psi -----------------W.G. (6psi spring) sees 6psi and dumps.

M.P. = 12psi ------B.C. bleeds off 8psi----W.G. sees 4psi (12-8=4) and does not dump.

M.P. = 14psi-------B.C. bleeds off 8psi----W.G. sees 6psi (14-8=6) and dumps, setting your boost level at 14psi (1BAR)

Does this make sense?

Hope it helps.

 

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 a profec do the same thing, but with Pulse Width Modulated solenoid valve.

 

okay that definately clears things up. Thanks!