Well RJC won't be open for a couple of days so I thought I'd ask you guys since some of you are using it. What is the range of boost it can control (min. to max)? What is that gauge pictured on the website?
Not hard at all. Similar to adjusting a regular wastegate. I just started out with RJC MBC screwed in just a couple turns (lowest boost), go for a test ride, and tighten it up (to increase boost) until you're where you want to be. 1 full turn equals about 1 psi. I've read you can also set it with compressed air but that kinda takes the fun out of making test hits trying to dial it in
Don't know, however Bison has my turbo now, maybe he will shed some light
The wastegate bypass cross section will dictate the lowest setting possible. Remove the actuator arm and hold it wot all the way through 3rd. Whatever boost it makes is the minimum it can make. Doesn't matter what controller is used. You will need a large bypass to run only 10psi unless you are running close to a stock turbo. Usually a very light spring (in an external gate) with an external source of pressure and a good smart electronic controller is required to have a wide swing of adjustability. You can open the bypass up to whatever size puck you have and then buy a few plates with no hole. Then you can make multiple plates with multiple hole sizes. The bigger the hole the lower the boost with any given wastegate tension. Big hole with light tension equals low boost. Small hole with heavy tension equals high boost. Trying to go below 70% of the mass flow potential of a turbo requires a very large bypass typically. The cracking point of the puck can be calculated if you know the spring tension, actuator diaphragm cross section, actuator pressure, leverage (or lack of), cross section of the puck, and exhaust pressure. There's no set in stone 1 turn equals 1 psi or any other internet fantasy. With my turbo all in I can still shorten the rod 5 more turns yet it doesn't matter because the tension is so high and the exhaust pressure not high enough to overcome it even with the pressure port on the diaphragm plumbed off the compressor cover where it's hitting the actuator with the highest possible pressure.
It may seem complicated but it's really not. It's the difference of the sum of the forces in each direction with any leverage added or subtracted from. Most don't consider the exhaust pressure because it's rarely mentioned. If you have a puck with 1 square inch of surface area and 22psi exhaust pressure then 22 lbs of force is on the puck just from the exhaust. Then say you have a 2 square inch area on the diaphragm with 20psi in the actuator you have 40lbs of force to complement the exhaust. So 62lbs of force in one direction Then the actuator spring is exerting 55 lbs of force on the arm (not counting and leverages in either direction). The puck has moved because the forces in that direction overcome the force in the opposite direction. It's easy to see why this is so variable. Different size bypass holes, different wastegate tensions, devices that reduce or delay the signal to the actuator (often called controllers), leverage changes, different turbines/compressors in different exhaust housings, and on and on. So many factors. Then take into account the typical exhaust leaks that are found bleeding off pressure and people are really wondering why their car is slower than John Doe who has the same "stuff" when in reality Johns car doesn't have the same stuff. Johns car doesn't have the exhaust leaks, poor tune, etc. Instead his car runs like it should.
The actuator can definitely have an effect because the tension it applies to the swing valve is a force holding it closed. Having a large bypass will cause a greater pressure drop when the puck uncovers the hole. The flow becomes just like an exhaust valve in a cylinder head. There's about unlimited possibilities playing with all the things that effect the boost.
Yes. Still not really complicated. GM had it nailed down to the point that if full pressure from the cover was sent to the port in the actuator with no bleed off boost was just about rock solid at 10psi. You can verify this any time with a near stock car with the stock turbo, solenoid, and chip. Simply unplug the solenoid and go to WOT. 10psi boost. Stock cars have the same actuator, same bypass hole cross section and same pressure source. There's other things involved but it is very consistent
