RCR S2

1) BOV opens when there is vacuum at intake -- i.e. closed throttle. This occurs when you are idling at the stop light, or when you just let off the gas after accelerating. At high rpm, with wide open throttle you have boost as opposed to vacuum, so the BOV is closed.


2) BOV relieves boost pressure. This means lowering it to atmospheric pressure.

3) The BOV relieves all the pressure when throttle is closed. Wastegate is used to limit boost to a preset point -- i.e. you still have boost. They are designed for two different situation. One when you're accelerating (Wastegate), the other when you're decelerating (BOV).

Keep in mind that the BOV also opens part way as well. When you are running high RPM and have the throttle half way, the BOV opens up slightly. It operates based on pressure differential between control line pressure (pressure at the engine side of the throttle plate) and intake pressure (the SC side of the throttle plate). The BOV tries to find equilibrium when both are equal. In reality there is also the spring force to take into account, but for this discussion we can ignore this.

Think of it this way. When you are WOT at high rpm, your SC is spinning extremely fast and generating high boost. If you close the throttle half way, the pressure on the SC side of the throttle plate spikes because the opening of the throttle body is much smaller than before. At the same time, there is less pressure on the engine side of the Throttle plate. This pressure differential opens up the diaphragm of the BOV and pressure on the SC side of the TB is reduced to a level where the BOV is at equilibrium. Thus the " Psshh "sound even at part throttle.

Wastegates operates on similar principles but uses the boost controller vacuum line for control. Purpose for wastegate is to have exhaust routed around the turbo to limit boost. But this can be adapted for the intake - but limited by size and fabrication ability.

BTW, typically a wastegate by itself is a purely mechanical device. It can't interpret MAP signals, rather it uses pressure to regulate.

RCR S2

Limiting Boost with a wastegate is good because you would not need to upgrade the injectors. It runs at 8 psi, but get's there at much lower rpm.

The draw back, of course, is that the SC turbine is actually running much faster than stock (assuming you're using a high boost pulley otherwise it makes no sense to do this) and therefore at the high rpm, even though the boost is the same as a stock SC, the air temperature is much higher and could lead to lower performance at high rpm. Ideally you should also increase cooling capacity.

The complex fabrication, cost, and temperature increases is why people shy away from this idea. But it can be done given the right resource$. As for me, nitrous assist is the way to go =)

modifry

Thanks for taking the time to answer my questions. I'm reasonably mechanical but have zero experience in this area.

[QUOTE]Originally posted by RCR S2
1) BOV opens when there is vacuum at intake -- i.e. closed throttle.

Pakisho

Getting back to those who asked. Here is what I got in a reply.

The setup is a vortech supercharger on a built, 3.2 liter v-6.

"It's ok for now. I hooked up my bypass valve to work electrically. I have an adjustable switch in the engine that activates the bypass valve after 13psi. I can adjust it from 5-15psi. The bypass valve cannot not release enough boost to keep it at 13psi when activated, but it bleeds a lot and keeps max boost around 15psi if you keep in the throttle. This is really a safety measure, as I usually shift only at 7K any ways.
I do not know if I will keep this setup or not.
I have been looking for an adjustable (preferably electronic) pressure regulator for the intake side for some time. I would have thought that someone would have made a product by now.
Something that works just like a turbo wastegate, but on the intake side of a S/C motor. It would be cool to limit the boost, then be able to up it to max if you get race gas, etc.
I have not found an obvious product that does this as of yet, but I might look again.
I think something like this would work best on a system with a stand-alone fuel management system that references boost. That way, not matter what the boost level, high or low, the correct fuel is delivered.
My SHO uses the LPM, and this only uses static fuel mappings for open loop, in other words, it cannot adjust for variable boost limits.
The best I can do is tune for the highest boost level, and when I limit the boost the ECU will run the fuel rich at the top end when the max boost is lowered.

Anyways, those are some ideas. I'll try to look some more into pressure regulator options, so far I have found none that are S/C specific and electronically controlled. That would be awesome.
Let me know what you find."


Dont know how much it helps, but he is on the right track, as far as getting more midrange out of his engine. But he's also short shifting at 7k for safetys sake (this setup is good for 8k, and will make power all the way to redline).

Darksyde

One thing that has come along that I didn't think of was the ability to go from a low boost to high boost setting. This would be good set up for pump and race gas.

I don't think that if you we're to use a wastegate it wouldn't have to be that big, say a Tial 35mm (the smaller version), it would be pretty close to the size of a BOV. It would like you're running 2 BOV's.

For electronics you could run AEM EMS with the boost control feature or the E-Manage with Profec-e01. All you need to do is run vaccum lines to operate the wastegate and have control of the vaccum from your choice of controllers.

I mentioned a POV because it doesn't need electronics to work but it didn't give the ability to adjust boost from the cockpit, it would work like a manual boost controller.

I started this thread to get more midrange power but it has opened to a boost controller set up for the supercharger but that's a good thing because I think that having boost controll on a supercharger would be a cool feature.

kstokell

How about a sort of boost resevoir that acceptes overboost into a pressure container and then releases it as the boost level drops?

Pakisho

Another guy I know with a blown sho regulates his boost via the throttle body..........that is something that could also be done. Because the throttle body will limit the amount of air that the engine will see.

Anyone?

kitwetzler

the ideal way to do this would be some sort of CVT in the supercharger gears, but I haven't heard of one that will withstand those kinds of stress in terms of rotational speed.

you're just not going to end up with a whole lot more boost. I had a supercharged M3 and it went from 8psi at redline ( 7000rpm )to 11psi at redline. At 5500, boost was essentially the same, I couldn't see a difference on the gauge.