EBC, weak spring - huge control range??

[HiProfile]

GOAL: increase the control range of an electronic boost controller. HOW: increase the pressure differential... I've received info that a typical EBC setup can control up to 2.5x what the spring pressure is in teh WG (given no boost creep). I was thinking what all is involved in opening the WG, and keeping it closed. You basicly need to keep the [arbitrary] pressure differential between the two sides of the diaphragm at that of the pressure exerted on the valve by the exhaust. With a weak spring you need a larger duty cycle to put more pressure on top. At a certain point, you can't go further (~2.5x over spring pressure, I'm told) I was thinking how to help increase this. Reduce the amount of pressure below, and you can greatly increase the differential you create... To do this, I'd think you could use a flow control valve to keep the bottom of the WG just above spring pressure. It would still open the valve, but will take a lower duty cycle to control the WG. So say you run a 5psi spring. A 15psi you see 15psi above/below, and the 5lb spring is your abitrary differential. Reduce the max pressure allowed below to 7psi, and you need that much less above to control the WG; conversely, you can run more boost pressure with the same amount of control. All you'd need to do is take a tuned car run it at the minimum psi your EBC can do (while active), add in the flow control valve (the type on your air compressor), and see what reducing lower WG pressure does to overall boost with a given duty cycle. At best I could see this helping a very low spring, say 3.63psi, to control at LEAST an extra 3psi, at most - another 5-10psi. In other words, maybe another factor in control (+1x spring pressure, so 3.5x). Only other downside I can see, the extended bit of range might be harder to keep at a consistent level. Any takers on this idea? I can't quite test it yet, so I can't disprove myself.

[calvin]

best way to that.. eg run 4 psi spring and boost 30 or 40 psi is with CO2

[butch11a]

can you give an idea how big the co2 tank is and how long does it usually lasts, what happens when it runs out, i assume the boost goes down to spring pressure?

[HiProfile]

I always aim for streetable stuff, meaning there's no room for consumables like CO2. I'm glad you brought that up, since this is a similar principal. Rather than increasing the pressure in the top of the WG, you are decreasing the pressure below it. I was thinking how you'd release that pressure when you shift or let off, since flow control valves are probably one-way. In place of a bleed hole, you'd just have to use a decent checkvalve or two. As the boost source goes below the regulator's pressure, it opens the checkvalve and bleeds into the manifold. I'm actually surprised expensive MBC's dont do this instead of the normal bleed hole. It could be a good selling point. As for the CO2 tank, it could be something rather small, like a paintball 20oz tank, or larger than a normal NOS bottle. You can have it pressurized at whatever level (welding tanks usually start at 1800psi or something), you just need a regulator/flow control valve like above to keep the outlet at a low 30-40psi. The problem is once it's gone, its gone. You'd have to manually switch to boost reference for EBC control, or have a 2nd solenoid to do it electronicly. And only way of knowing its gone is a pressure switch/buzzer, or just noticing the boost gauge never going above spring pressure...

[mafdark]

anyone ever make a mechanical waste gate? With ECtune controlling it I would think it would be easy, no springs needed.

[HiProfile]

It could be done, but you'd need a 4-way solenoid valve, and it will be limited when it comes to high boost depending on the design. Low boost would be easy though, as long as it can't be pushed open by exhaust pressure. It could work if you made the diaphragm 2-3x as big, and/or used a flapper-style to multiply the torque on the valve.