Blow Off Valve????

MAXVELO · #1 (**permalink**) 11-18-2003, 06:57 AM

Can anyone shed some light on the application of the blowoff valve? I know what its for. It works like a wastegate on a turbo. but is one required for my application? When I bought the car from WELD MOTORSPORTS it did not have one. I am in the process of re-doing the air intake plumbing and supercharger bracketry. I am just wanting to know if I need to install a blowoff valve to regulate the boost or can it be done with different sized pulleys? Any feedback would be appreciated!
Gary Mirabal

Wade Chamberlain · #2 (**permalink**) 11-18-2003, 08:43 AM

You would typically use different pulleys to adjust boost on a supercharger. A blowoff valve usually isn't used like a boost controller. It's typically there to protect the throttle blades from high backpressure when you let off at higher RPM's. Most folks don't run a blowoff valve unless they're over about 6 PSI of boost.

HighPlainsDrifter · #3 (**permalink**) 11-18-2003, 10:01 AM

Gary,
The blowoff valves are typically used on road race cars or small engines with turbo's. The blowoff valve would release pressure and is usually routed back to the front of the mass air meter on EFI cars so that the computer sees a closed loop of air for proper fuel management. This aides in on/off throttle and reduces heat and lag in small engines.
A mechanical supercharger does not need it, you would also need about 4 of them to pass the volume of air in your MONSTER motor if you wanted to use them.
Perry.

Wade Chamberlain · #4 (**permalink**) 11-18-2003, 10:59 AM

On a mass air car, the air would be re-introduced AFTER the mass air meter, not in front of it. If you reintroduced the air in front of the meter, you'd be "re-measuring" air that never entered the engine.

In the case of a mass air setup, the proper term for the valve would be a "bypass" valve, not a blow-off valve. The blow-off term implies that the boost is released to atmosphere, like would be typical in a speed density type of EFI (which I'm guessing is what Gary has).

MAXVELO · #5 (**permalink**) 11-18-2003, 12:13 PM

Thank you Gentlemen, for all your inputs . I didnt think I really needed on but if I did I wanted to make sure I plumbed for it.
Gary