OK , I have lets say 10 psi of pressure going to a PV chamber from a hole coming from the top of the carb that sees hat pressure .

If I leave that hole and add pressure to the PV chamber from an outside air source , lets say 20 psi where does that leave me ? If there is 10 psi from one source and 20 psi from another , where does that leave the pressure in the chamber ?


Cue Jeopardy music .

 

How big, and how long is that hole? I could be totally wrong here, but I would think that the extra pressure in the PV chamber would go out that hole and try to equilize with the pressure in the carb hat. So its all about the hole size and length to figure out how fast it can vent that extra pressure in the PV camber to the hat. But then again, I could be totally wrong on this, but that is my thinking....
Bowtie Guy

 

also is the PV chamber blocked off from its regular passage way to the bottom of the carb?

 

Not sure yet .

Thats what I thought too . I was just wondering how much more pressure it would need to maintain the same pressure in the chamber .

Reason I want to keep the reference to the hat is because I wanted a fail safe in case the air compressor failed .

I could set the BRPV at a higher opening rate like 10psi . Then I could control it with the outside air source to open at anything under that . So if I'm WOT making 15psi of boost and the air pump failed , the power valve would still have a chance to stay opened .

Does this sound right ?

 

It sounds right to me. After looking at you hole sizes in your build thread, I'm wondering if you couldn't tap the hole and put a reduced size hole insert. That way if it doesn't work, you can remove it, plus with the reduced hole size, you can use a smaller psi air pump, plus in case the pump fails, you will have enough boost pressure in the hat to keep the BRPV open even with the reduced hole size. I'd leave the PV set at 5 psi for this reason.... JMO But I've been thinking about doing the same thing your discribing, but my setup runs so dam good that I'm afraid to mess it up lol
Bowtie Guy

 

Yea I know what you mean . Mine is running fine , but I just like the added insurance that the PV will stay open at higher boost levels .

I guess I also just like tinkering with stuff , that's all .

I've got lots of other things to mess with for right now .

I'm just trying to get some ideas .

 

You will always have suffecient pressure in the hat to open the valve. Whay do you want to add more air to it. The only problems people saw with valves closing off at high boost was the regular style valve. Those were referenced to the manifold. As the boost rose the pressure differential in the bowl/hat got bigger and bigger until the point of the hat pressure overriding the spring pressure holding open the valve. You have none of those worries. The more pressure in the hat the more pressure in the PV chamber forcing it open...

 

I was thinking the pressure in the bowl was equal to the pressure in the hat .

Plus the bowl side has added help . The spring . So the bowl side would need 5psi less than the hat side to have the same pressure . ( if that makes any sense )

But this cant be true or the BRPVs that I have wouldn't work . Right ?

 

Yes it is.

I am not familular with the design on the valve on your PV. If a regular valve that was converted, just using a spring on the back side of the valve. The problem with those were the pressure in the chamber would open the valve and then the fuel would start to flow. The pressure would then equalize against the diaphram then the spring would close it. That cycle would start over again. I am assuming they have found a way to prevent this from happening because this is very hard on the diaphrams. The valve is probably designed to not have fuel on one side of the diaphram at all. Is this a stretch... Maybe??? Do you have any pics of the valve out of the metering block?

 

As far as I know , thats how it works . It uses the spring top hold it closed until pressure on the diaphram is enough to over ride the spring .

Thats what worries me about turning up the boost .


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Say you need 10 psi on the diaphragm to open the valve and keep it open.

Lets say you have an 1/8th inch hole feeding Bonnet air to the PV Cavity.

The pressure in the bonnet would have to be slightly higher than 10 psi due to passage losses to open the valve.

You also have an 1/8th inch hole feeding external compressor air to the PV Cavity.

Right off the bat, the Compressor Air would have enough flow to have 20 psi at the PV cavity to keep the valve open because you would have a 10 psi "leak" to the Bonnet. The flow in the "Bonnet" passage would reverse.

Suppose the compressor failed. Would it fail in a "closed" mode where there would be no "leak" and now the "Bonnet" pressure would still open the PV at 10 psi? What if it failed in a "Open" mode. Now you engine has to see 20 psi for the PV to work. Bye Bye Engine. A "One Way" Check valve in the system designed to work with boost might save your engine if the compressor developed a "leak". Then the "Bonnet" boost would work in a "back-up" situation.

The Check Valve might need some fine tuning as there would probably be some delay in the valve unless the valve had a high flow capacity.

Some things to think about.

Tom Vaught

 

Tom ,

VERY good points . I didn't even think about the line to the compressor being open during a failure . The check valve would be a must .

So your saying , if there is 10psi at the hat , I would need 20psi from the compressor to maintain 10psi in the chamber ?

Plus , wouldn't I need to keep the hole going to the base plate so the PV closes quickly when the throttle blades shut ? If thats the case it would need even more pressure from the compressor to keep it closed .


A check valve on the compressor line would keep the PV open during deceleration until the pressure in the cavity is bleed off somehow .

It seems like it would take too much time for the hat pressure to come down enough to close it .

 

I just had a thought. To help ease your mind... You have measured a 4 psi drop though your intercooler right. Well there is your source of higher pressure air that is fool proof. It only provides the air when needed. You could try running a larger line to the chamber and see what happens. Or seal off the hole in the top of the carb and use only that higher pressure source... Think about it. The more boost you add the higher the differential pressure across the intercooler the more pressure is holding that power valve open. Sounds good to me.

 

Actually that 4psi drop was the difference in the compressor and manifold . I havent checked the drop between compressor and hat .

I think I understand what your saying , and I have thought of doing that way , is using a line from the turbo compressor through a solenoid then to the PV chamber .

Is that what you meant ?

I didnt think the pressure difference between the compressor and the bowls would be great enough .

How much difference could it need ? 1 or 2 psi ? If so then the restriction in the intercooler should be enough of a difference to keep the PV open because the bowl pressure would never see as much as the compressor pressure .

And if the hole in the carb that referenced the chamber is blocked off , then it would for sure be more than bowl pressure .

You might be on to something here .

You wouldn't need a solenoid to do it either , you could just adjust the PV spring . The solenoid would just allow you to do it from the drivers seat .

 

Hmmm. Not 4 psi but yes that is exactly what I am saying. If the extra pressure makes it come in earlier than desired you could use the solinoid. It would be nice to get the spring just right and not have to worry about any electrical failures. Time to do some pressure testing. FYI it is -37* here.

 

Not here . :cool3:

 

I was just out driving around to check some pressure at the turbo compressor .

If I put some load on it and bring the RPMs up staying JUST out of vacuum on my vac/boost gauge . ( right at zero ) I'm seeing 10 to 11 psi at the compressor .

So it looks like it would need a solenoid or the PV would open way too early .

 

OK . Now my brain hurts .

 

Looks like the best way would be to do it with a air pump and just make sure it produces enough air pressure to over come the hole in the carb thats seeing hat pressure .

 

No not nessearily you are measuring the boost at the compressor when the throttle blades are not open all the way. At that point the hat is reading the same because the blades are causing the backup of boost. I was interested in WOT numbers between the hat and the compressor. That would let you know what the pressure drop was between the 2. That way you would see how much more pressure there is at the compressor vs the hat. Once you find that out, if there is enouph pressure differece, you can set up your reference line to the PV chamber though the side of the mainbody and seal the hole in the top of the mainbody. You will then have the peace of mind that the valve will be open at higher boost levels. How much this will throw out the calibration of the BRPV is yet to be determined.