Which is better for turbo setup: BOV or Dump valve?

debo890 · Post by **debo890** » Mon Jun 26, 2006 9:55 pm

its all about prefrence. you can install it close to the intake, close to the turbo outlet, or in the middle. it really dont matter. what matter is the responce time you want. if you want acurate ( fast responce) psi control, you want is closer to the turbo outlet. if you want a slower responce and have you turbo bulid some psi over the set psi then closer to the intake manifold. if you want best of both worlds, put it right in the middle. eventually, it will vent the air. it just depends on what responce you want.

M I N I O N · Post by **M I N I O N** » Thu Jun 29, 2006 9:00 am

I hate to break this to you guys, but when you have a large volume charged air system and you put a blow-off valve anywhere on the pipes, you are going to lose all stored boost and your throttle response is going to go with it. When you shift and the throttle plate closes, you aren't just losing the boost you had built in teh previous gear, you are also decreasing the amount of CFMs the engine is flowing DRASTICLY. All of the sudden your little 1.5-2.2L engine is spinning half as fast and has no added pressure to work with, which hurts your respeonse even more as you have lower EGTS. It's all happening over fractions of a second though. People generally put the BOV closer to the throttle body as this is where the pressure surge is going to start so dispursing it here is going to give less of a chance for the pressure to run back all the way to the compressor wheel and surge the turbo in any way. The best part is that by adding it here, you have a surge of air molecules still flowing through the pipes to leave the BOV near the TB, which in turn works like back pressure in an exhaust system to get the wheel moving quickly again.

Most drifitng teams run without a BOV to increase throttle response when feathering the gas durring drifts. With as much boost as they run, they rebuild their turbos monthly or bi-monthly to replace the damaged bearings and compressor wheels if necessary. The drag teams are going either or... In all reality a BOV does not affect them since they are all converting to automatic transmissions and don't let off between shifts.

For a street car, use a BOV. Placement it optional but for the sake of performanc, it is better to keep the velocity in the charge piping and run it closer to the throttle body.

A diverter valve is a BOV that routes the air back into the intake tract after the MAF sensor to keep MAF cars from getting a momentary choppy idle after letting off the gas from losing metered air. The recirculated air is already hot so there is really no performance gain.

woo · Post by **woo** » Thu Jun 29, 2006 2:51 pm

i have a good friend who is a mechanic for scuderia veloce porche, and what he has been taught is that BOVs are purely for show. Apparently you loose boost between gears, therefore the car has to spool everytime you shift. Then he went on to say, that if they were the best setup for turbos, wouldnt a 911 turbo have one? which made sence to me because there was alot spent to develop that car, and recurculating valves are there for a reason. Also, i know that at the drags, all the fast turbos (PAC racing rotors and such) are autos. They have the stall converters at revs just higher then what the turbo spools at, eliminating lag all together

M I N I O N · Post by **M I N I O N** » Thu Jun 29, 2006 5:33 pm

It hasn't been until very recent that PSSSHHHHHHHHHHHHHHHHHHHHH has been an acceptable sound to come from a factory car. There is really no performance advantage to blowing hot air at a closed throttle plate. You've got an intake filter on the other side that prevents you from adding any sort of pressure in the intake piping and the TB is closed, meaning it isn't going anywhere else. Basically all you are doing is stopping the MAF from reading any more incoming air so that it doesn't get rich and bog. Diverter valves are used in MAF applications because they have to be and usually are in other application just because the intake piping will help to filter out that noise. In the future you will see more companies using BOVs as opposed diverter valves.

Another thing you have to think about is that some custom turbo systems have the fitler directly on the turbo. Example, my own:

Where do I recirculate to?

In all reality "I porsche did it, it must be right" isn't exactly a valid argument in this case because there are lots of reasons for doing things differently in every othe car on the market.

klonek78 · Post by **klonek78** » Fri Jun 30, 2006 4:18 pm

1. in europe using BOV is prohibited because of ecological issue..... etc so do not expect car with factory installed BOV - DV rulez.....

2. we have the strongest Audi S4 in europe (over 1000HP - 9sec. car

) and there is BOV installed....

M I N I O N · Post by **M I N I O N** » Fri Jun 30, 2006 8:25 pm

Pictures?

What is the ecological issue? Is hot air bad for the whales?

klonek78 · Post by **klonek78** » Fri Jun 30, 2006 9:17 pm

M I N I O N wrote:Pictures?

What is the ecological issue? Is hot air bad for the whales?

because this hot air can contain few oil drops.....

pictures od this S4??

http://photos.sss.org.pl/norwegia/22.jpg
http://photos.sss.org.pl/norwegia/28.jpg
http://photos.sss.org.pl/norwegia/36.jpg
http://photos.sss.org.pl/270506/73.jpg

M I N I O N · Post by **M I N I O N** » Sat Jul 01, 2006 12:49 pm

Hot air only containes oil if the PCV is recirculated to the inlet of the turbo which isn't done on most cars and a catch can would fix. Also if the compressor seal is busted which you would know about.

That S4 makes me happy.... They could have at done some cutting to get some air hitting that intercooler.
/sarcasm

klonek78 · Post by **klonek78** » Sat Jul 01, 2006 11:48 pm

M I N I O N wrote:Hot air only containes oil if the PCV is recirculated to the inlet of the turbo which isn't done on most cars and a catch can would fix. Also if the compressor seal is busted which you would know about.

don't tell me that, I don't make cars

BTW. S4 is cool car but that one is little stronger and faster..... called GMC Typhoon (also from Poland

)

http://photos.sss.org.pl/270506/55.jpg
http://photos.sss.org.pl/270506/72.jpg
http://www.fotorelacje.com/displayimage ... =26&pos=34
http://www.fotorelacje.com/displayimage ... =26&pos=35
http://www.fotorelacje.com/displayimage ... =26&pos=60

M I N I O N · Post by **M I N I O N** » Sun Jul 02, 2006 12:09 am

We have those in the states.... they stopped making them because they were faster than the corvettes of the same years. turbocharged, awd 4.3 vortec. ::drool::

MMamdouh · Post by **MMamdouh** » Sun Jul 02, 2006 10:01 am

so the bottom line on this issue is to use a DV for better effecency... now i got all confused about where to put it... TB or turbine.

MMamdouh

Stefan · Post by **Stefan** » Sun Jul 02, 2006 11:25 am

I'll still stand by what I say. I've been very lucky that this year, and especially since getting another job, that I've been exposed to people working at top levels of motorsport - WRC, Le Mans, etc. My working knowledge has increased alot and the information I have access too has increased also. It has made me see advice given on internet forums in a very different light... It is no surprise that professional motorsport engineers rarely post on such forums only to get rubbished by people that think they know better because of the latest trend in "tuning"...
This is not a dig at anyone, I'm just fed up with the internet... I rarely feel able to give advice anymore when I get the time too.

All I can say is to experiment, record results and decide for yourself what works...

Stef

MMamdouh · Post by **MMamdouh** » Sun Jul 02, 2006 12:13 pm

thaks for the info.

not all people got lucky to be so close to top levels of motorsport tuning shops and all as you did but almost every one got internet access so they will seek knowledge through it... maybe it is your responsbility to set the record straight when it comes to such debated issues based on the knowledge you have aquired, right?

MMamdouh