Contour Enthusiasts Group Archives Forums Modifications Forced Induction blow off valve

this might be stupid but what does a blow off valve do

Can you put one on a Supercharged Contour.If so Has anybody done It??

A Blow off valve is used to keep a system from overpressurizing.

It is often used incorrectly & refered to instead of using the correct terminology for a "Bypass Valve" when talking about the valve used to vent the boost between the turbo and the throttle plate when the throttle plate closes.

You know. The whoosh sound when shifting. :p That's a BYPASS VALVE, not a blow off valve.

Forced Induction ettiquete police 101

(Below stolen from of all places; my website )

Bypass Valve = is used to stop compressor surge from happening. See compressor surge. The bypass valve in turn allows air to be rerouted and sent back through the turbo inlet between shifts allowing the turbo to keep spinning so spool up time will be quicker. Please understand that the HKS racing bypass valve does not reroute air what it does is allow the wheel to spin freely once the valve relieves all the excess pressure trapped within the intake between shifts. A Bypass valve will also extend the life of the turbo.

A Blow-Off Valve is NOT the same as a Bypass Valve. A Blow-Off valve is a safety device that opens at a set psi level to prevent over boosting the motor

Compressor Surge = when the throttle slams shut and air is caught between the turbo and the throttle body. Air is then forced backwards toward the turbo causing the unneeded stress to occur on the turbo compressor wheel and shaft. This can cause after extended periods of time turbo failure. The use of a Bypass valve will end this event from happening.

that would be the wastegate

Yeah, i think what you are referring to is a wastegate, not a blowoff valve. A blowoff valve only activates during shifting to keep the turbine spooled up. It also relieves back pressure on the turbine during shifting to help increase it's overall life. So the answer is no, this would not work on a supercharger.

Cheers
rimmie

Can you get The whoosh sound when shifting.with the Contour S/C??

There is a little bit of truth here. However none of you are completely clear as to what any of the devices are or how they are used. Do some more research!

A wastegate is someting differently entirely. It holds the turbo producing a set boost pressure.
It is necessary. A blow off or safety valve is not. A Blow Off valve vents all pressure AFTER the turbo to prevent the engine from being damaged by overboosting.

If you are going to try and correct someone. Atleast do it right...

Wastegate = is an opening that can circumvent the exhaust wheel allowing the turbo to stay at one particular boost pressure. Wastegates can be internal or external to the turbocharger.

Wastegate Actuator = a pressure operated diaphragm with a rod that is connected to the side of the turbo. The diaphragm receives its signal from the pressure within the intercooler lines. Once it senses that the set boost level has been achieved then the diaphragm pushes the rod allowing the turbos wastegate to open releasing excess boost pressure.

Then rimmie made the cardinal sin again of calling a Bypass valve a Blow off valve... AGAIN... :rolleyes:
Reading is key to learning folks... :p

pitsvt - Yes it would be possible if a Bypass Valve was installed between the S/C and the throttle plate and vented back into the intake after the MAF. Not very feasible or practical given the setup, but possible...
After all The Vortech unit is just a belt driven centrifugal turbo or a turbo is just an exhaust driven centrifugal supercharger...

Although I agree they are different, I thought they had the exact same purpose??

Bypass valves are used on MAF engines (Porsche/VW/etc) where venting air that has been metered is not an option.

MAP sensored engines (Honda/Toyota/etc) can have a valve simply blow air outta the intake tract to prevent compressor surge, simplifying plumbing, ang giving out the lovely "pschht" that everyone craves.

But to me the functionality is the same, isn't it? They both prevent overboosting (to an extent) but they both mostly work against compressor surge as well.

Hence I don't think rimmie is so far off. Overboosting is controlled by the Wastegate... Isn't it?