Vacuum controlled systems with boost, what to do?

[BlackFox5.0]

What should I do about everything that operates on vacuum when I hit boost? I think that might be the reason my AFPR gave out because the boost might have collapsed the diaphram inside.....I think I'm going to put a check valve on the FPR until someone tells me I should do otherwise....

 

[Rick 91GT]

The biggest thing is to make sure your FMU (if you run one) and your boost guage are on individual ports or they will steal vac from eachother and not give you good results or readings.

We've ran both a Kirban stock style regualtor and a off rail Aeromotive with no issues, so a check valve is not needed. The vac source it staright from the Cobra manifold.

A lot of guys with big race blower end up going to manual brakes since the booster can actuall see boost, you can even feel this soe times with the smaller blowers 8-10psi when you first go to hit your brakes.

 

[astronut1885]

You can hook them all up to a point before the blower, where there is vacuum. Make a fitting to attach vacuum lines somewhere near your MAF.

 

[BlackFox5.0]

Rick, I don't know if you remember or not, but the Kirban is the one you sold me. I don't know why it's not working anymore, but it's not. I'm only running 6psi from my blower.

Rob, if I put it before the blower the vacuum there should be greater than what the engine would have if it didn't have boost going to it, giving improper fuel or whatever because the vacuum is greater....

 

[Rick 91GT]

So it did work fine but since the blower install it isn't working for you? Try moving the vac source first, to a dedicated source you have issues. Why do you say it doesn't work, or you think the diaphram is collapsed?

Putting the vac source before the blower is not a good thing.....

 

[BlackFox5.0]

Well I had it set at 51psi before, then my car has been acting up really bad, so I checked it, and it read 25-30psi without vacuum, so I tried turning the screw both ways and the gauge needle didn't move at all. I put vacuum to it and it didn't move, revved the engine, barely moved, maybe 1-2psi, thats it. I also tried adjusting it with vacuum, and nothing....i thought the guage might be reading wrong, but when I shut the car off the pressure went down, so it was wroking, and there are no leaks, i don't and didn't smell any gas.

 

[astronut1885]

On an AFPR, the vacuum doesn't do much since you control the fuel pressure with a manual diaphram. If it was a stocker, then vacuum plays a bigger role. By connecting it after the blower, you forced 8 psi into that little AFPR, compressing the internals and thrashing it. If you attached it before the blower, say near the MAF, then there would be no vacuum, so what I said earlier is pointless. It has to be put after the throttle body. either a 1 way valve like on a brake booster has to be installed, or you have to run it vacuum off.

 

[Azul93GT]

I'm don't understand something here. Doesn't the vacuum pressure originate in the upper intake manifold? How does a person select a vacuum source before the blower?

 

[Js5ohLX]

Like the air intake. When you add boost, you remove the vacuum and add positive force.

 

[BlackFox5.0]

I'm don't understand something here. Doesn't the vacuum pressure originate in the upper intake manifold? How does a person select a vacuum source before the blower?

You can get vacuum before the blower in the supercharger inlet I believe.

 

[astronut1885]

There won't be vacuum there chris. It's next to the open air filter, so there isn't enough pressure built to really activate the vac systems, or so I'd think. You'd be better off adding some check valves like the brake booster has. Also, the PCV is a one way system, so that's not a worry. Pull your PCV valve and blow into it. Nothing happens. The AFPR should be able to stand it, and the additional pressure will increase your fuel pressure a tad, which could be a good thing in boost conditions. The brakes already have a check valve, so you should be ok there, unless you go pushing big PSI.

 

[BlackFox5.0]

Who uses brakes during boost? The brake booster has a check valve already. All mustangs have one there. The PCV valve is a one way valve, but it doesn't not seal good.

 

[BLOWN 5.0 FOX]

adjustable fuel regs are like an fmu but they are generally speaking 1:1. The boost actually helps the fuel curve by adding fuel pressure. As long as your tune AFR is good, you have nothing to worry about. I have my pcv system run to a catch can and then to the inlet of the blower on the power pipe. this is the safest way to run a pcv system since the valve will always draw the excess pressure from the crankcase.