This Tech Article is more a primer to give more information of the workings of a 1G BOV (or BOVs in general) and the two common mods used to improve upon it's design to sustain higher boost levels without leaking. I've included links to the Tech articles covering these mods in more detail.
Background:
A BOV acts to release boost pressure between the turbo and throttle body when the throttle plate is shut. This is good for two reasons:
1.) With the pressure released the turbo will continue to spin freely = better transitional boost response (quick spool btw gear changes)
2.) The pressurized air would otherwise hit the closed throttle plate and like an ocean wave, reverse course making it’s way back to the compressor causing it to abruptly slow, possibly causing damage to the wheel.
The 1G BOV while infinitely better than the crappy plastic 2G valves, is still an OEM piece that was never intended to boost much above stock levels (13psi) and will leak at higher boost levels.
It is important to first see how a BOV works to figure out how to improve upon it.
The below pic (minus the air fittings on the mounting flange) are of a 1G BOV. The “top hat” section of the BOV contains a diaphragm and spring which is used to raise/lower a valve at the bottom based on air pressure on either side of the diaphragm combined with the spring tension. The
Blue lines represent airflow from the UIP and the
Red line airflow from the behind the throttle plate.
The BOV in stock form uses both air pressures to operate the BOV. When under boost (throttle plate open), the
Red and
Blue pressures are
equal and the BOV’s valve will remain closed based solely on the top hat's internal spring pressure (well until too much boost force on the valve itself overcomes the springs tension and pushes it open).
When the throttle closes (btw gear shifts when you let off the gas pedal), the air pressure in the UIP remains positive (
Blue), but the air pressure behind the throttle plate goes to negative (
Red). This is what helps the BOV to “quick release” as you have complementary forces (
pull=Red /
push=Blue) at work to open the valve.
This is all good at OEM boost levels, but once you turn the boost up, the pressure inside the UIP can force the BOV valve itself to unseat (blow it open), much like what happens to an upgraded 38mm wastegate flapper if the actuator is not strong enough.
When this happens, you are loosing boost pressure, which the turbo will have to work harder (faster RPMs, more heat, less efficient) to maintain. If you are running 18psi at the intake and you are loosing 2psi from the BOV, your turbo is actually running at 20psi (well more due to pressure drop across the IC/Piping but that’s fodder for another tech article :) )
Dodge Garage Mod :
The Dodge Garage mod seeks to block the
Blue line (UIP Pressure) so that only the
Red line (Intake pressure/Vacuum) influences the BOV operation. So now instead of equal pressures above/below the BOV diaphragm under boost, only the top section (
Red) from the intake is being fed, so you have additional downward pressure on the BOV valve equal to the boost pressure you are running. More pressure = more boost can be run before the spring/valve is overrun.
To do this, this mod involves "plugging" the inlet on the bottom of the BOV flange (JB Weld) that fed the underside of the diaphram with air pressure, and drilling a hole in the original passageway to relieve any pressure from the underside of the BOV diaphram.
I took this a step further and drilled a second hole on the opposite side the original boost feed and again in the flange to give me the the option to have "quick release" if I ever wanted it (which I haven't). Connecting the two new air tubes will give me OEM BOV operation.
Crushing:
"Crushing" the BOV just means sticking the piece in a vice and pressing the top had down causing the internal spring to shorten and increase pressure on the BOV valve.
Warning, crushing too much will prevent the BOV from opening enough/at all and will cause boost surge. I crush mine so the boost nipple is flush with the middle tier of the top hat (as far as it will go without bending the nipple) and holds well to 25psi ;)
Combining both these mods will elevate the boost threshold even further :)
