SpeedFreak03

Im pretty new to the turbo world (I know a bit but I've never actually owned a turbo car). Anyway before I get my TurboII I wanted to make sure I understand how boost controllers and wastegates work, I tend to mix their "jobs" up. Anyway, here is how I think they work, so please correct me if I'm wrong:

Normally there is a vacuum line going from the turbo to the wastegate acuator, correct? And when the pressure in this line reaches what the wastegate spring can hold, it snaps shut (or open?) and the exhaust gases flow out the exhaust instead of into the turbo, correct? Now a boost controller goes in between this line, and acts as a valve (well MBCs technically are valves ) to prevent how much pressure gets to the wastegate, so the turbo stays open longer and builds more boost, right? I really think I have it all down pat now, but I just wanted to be sure. Now if that is right, I have another question about how BOVs work:

OK this also confuses me a bit. First, the vacuum line coming off the BOV is the same one going from the turbo to the WG actuator right (like is it teed off of that line)? If so, then I understand that part. But what I don't understand is this: Lets say you buy a BOV that vents into the air, like the TurboXS Type-H RFL. Why does it have to be hooked up to somewhere in the intake piping, if when it blows off it doesn't go back into the intake system (it goes out into the air)? Wait I think I can answer my own question: Is it so that the BOV can detect when the throttle plate snaps shut (like all the intake air will stop moving)? Sorry about the motherload of questions, but maybe this could be added to the FAQ or something once I correct it (if it needs correction )? Thanks for all the help, BTW I've really learned a lot about 7s in general in the past month that I've been here!

RETed

That's all basically correct.

A wastegate is a mechanically actuated door.  The wastegate is connected to the vacuum actuator via a mechanical linkage.  This actuator has an internal spring that is calibrated to "give" when enough boost is applied to the other side of the diaphram.  That vacuum line going into the actuator triggers the WG when it actually sees boost (higher than the internal spring force).

A boost controller is plumbed inline, and it typically bleeds off the boost pressure trying to overcome the WG actuator internal spring.  By bleeding off the boost pressure, you can keep the WG shut longer which allows the exhaust gases to push the turbo more.  Thus, higher boost is achieved.

A BOV is another mechanically actuator valve that is triggered by vacuum.  THe BOV vacuum line needs to be plumbed into the intake after the TB.  This is key, as this is how the vacuum force is generated to trigger the BOV.  Once the TB is slammed shut when you lift off the throttle, this creates a huge vacuum area behind the TB, which in turn triggers the BOV.  The BOV also has an internal spring which force needs to be overcome by the vacuum force generated by the heavy decel.  With the stock FC3S fuel system, venting the BOV to atmosphere causes an instantaneous rich condition - this can sometimes trigger flames out the exhaust.  Most aftermarket BOV's are sealed tight enough to be used open vented; the stock unit cannot as it leaks slightly when open vented.  A slight intake leak if we try and open vent the stock BOV will cause idle headaches.


-Ted


-Ted

SpeedFreak03

Thanks Ted for the informative response! Now I really understand all this. Especially the part about wastegates - I thought it was something different lol. Thanks again!

Evil Aviator

You were probably thinking of a "pop-off valve" (POV) (aka Relief Valve), which was a way to control overboost a long time ago, but now it is just used mostly as a safety device or as a boost-limiting device to keep race cars within the rules for max boost limits. The POV opens very quickly, venting boost nearly instantly. This would make the car difficult to drive vs. the smoother and more gradual wastegate movement, and it would be pretty hard on the components if the POV vented on a regular basis.
http://entertainment.howstuffworks.com/champ-car10.htm

MountainTurbo

Hey, thanks for asking that question, helped me out too

SpeedFreak03

Yea a pop-off valve is what I thought a wastegate was! Learn something new everyday! Thanks again man!