SLiCKYV

Just wondering, the bypass valve on the comptech, is it the same as a blowoff valve? If not could you put one on and have it sound the same as a turbo's bov? Will it blowoff when you shift?

KAMcDonald

no, on SC the bypass valve gives the compressed air out of the blower a place to go when you get off the throttle since the butterfly valve is no closed. it can be released to atmosphere or routed back before the blower.

on TC the blowoff valve releases pressure at a certain point so you do not exceed a safe, maximum boost pressure to keep the engine from going boom

people have talked about using a BOV on SC along with a smaller pulley to get more boost lower in the RPM range, and still stay safe on top end. i know it has been done with other cars, not sure if any of us has tried it on an sek yet.

keith

TalonTid

that is totally fasle McDonald. Both the bov and the bypass valve are the same. They call it a bypass valve because sometimes the air is routed back into the intake tract. A bov on a turbo car "blows-off" when the throtle plate is closed , like when you take your foot off of the gas. All of that air is now rushed backwards towards the compressor wheel of the turbo and now forces that wheel to spin in the other direction after it was already spinnin at almost 10,000rpm the other way. The bov blows the air that would hit the compressor wheel into the atmosphere so that the compressor wheel won't be damaged, and the same principle applies to a supercharged car. Boost control is left to the wastegate on a turbo car, where at a specific bosst level a spring opens the diapraghm of the wastegate and routes the exhaust around the turbo to keep the boost at steady psi. Hope that helps.

SLiCKYV

So I can still get the cool sound outta a bov on a supercharger? Yeah it's kinda a lame reason, but I think it sounds pretty cool when my friend goes through the gears on his sti.

alexf20c

honda9krpm

you can certainly see a generation gap with this discussion j/k

in the old day before map sensor I am not old but just want to add some fact into this as to why kammacdonald is not too incorrect......there is a thing called "blow off valve". This was really a pressure leak valve as there was no map/electric cut defender. So it works on the theory of what kammacdonald mentioned.

Once the map sensor was introduced, these pressure leak valve was "junked". The ECU can now see boost and cut the engine with fuel/ignition.

BOV was reintroduced to save turbo and improve turbo lag. Most turbo car has a factory recirc BOV for noise reduction. Now, most ppl want that loud fart noise

All BOV work on the same principle.
For some of us SC addicts, the ideal thing to get is this pressure leak valve in 15-20 years old turbo car. It's very difficult to find though.

xviper

[QUOTE]Originally posted by TalonTid
All of that air is now rushed backwards towards the compressor wheel of the turbo and now forces that wheel to spin in the other direction after it was already

alexf20c

Well, your pistons will never spin in the opposite direction either, but if you have preignition they'll most definitely think about it, and tear up your bearings in the process.

Jip69

Slickyv ...... I too enjoy the BOV sound. I bought the non aftercooled comptech charger and my shop totally got rid of the bypass valve. The BOV needs to be mounted to the pipe that goes from the charger to the throttle body.

This is what I got out of doing a search and reading many posts on similar matters.

Air is constantly going through the intake through the blower and through the throttle body as you probably already know. There is a flap that opens and closes allowing mor air to flow through the throttle body. when it is closed, to not have all the air build up and cause damage air has to be pushed somewhere else. The bypass valve takes that air and pushes it back into the tube that is between the intake and the blower. so its basically recirculating the air. The BOV will push the air into the atmosphere making the psshh sound, so the air is not recirculated, its blown out.

Hope this helps.
JP

AusS2000

I am under the impression that the only difference between a BOV and a bypass is that the BOV vents to atmosphere (and is often designed to make as much noise as possible) whilst the bypass vents back into the intake tract.

I'm running an 8lb pulley on my Comptech and if the car was hot and idling and then I accelerated hard it would often stumble. I suspected this was because hot compressed air was being fed into the intake by the bypass and when I opened the throttle it was being sucked straight into the engine.

So I disconnected the bypass from the inatke and blocked the hole. Instant BOV. It doesn't make the fart noise, but then I'm not a ricer.

The pressure release valves we used on old carburetted cars were referred to as 'pop off' valves.