Blow off valve location

930 porsche · 07-09-2009, 09:21 AM

1978 930, where is the best location on a 3.3 to put a blow off valve?[

WERK I · WERK I's Garage

Didn't your Kokeln IC come with the 965 style rubber elbow and BOV kit? Most people have replaced the 965 BOV and replaced them with a billet type BOV due to reliability concerns.

930 porsche · 07-09-2009, 12:10 PM

No. I just replaced it with a full lenght intercooler. Also my intake pipe is going to my turbo from the rear flare not inside the engine.

930 porsche · 07-09-2009, 12:18 PM

Is it true that by going outside the left rear flare with a 3" steel pipe to the turbo charger will get better performance than going inside the engine like your picture shows?

A930Rocket · 07-09-2009, 12:24 PM

I've seen them located on the pipe from the turbo to the intercooler.

Not my car, but a nice one!

A930Rocket · 07-09-2009, 12:28 PM

Are you just re-routing the pipe or are you EFI and wanting to place an air filter in the wheel well?

The stock pipe might not be optimal, but it works well. Placing the air filter in the wheel well brings up a host of problems (dirt, water, road debris, etc.).

Quote:

Originally Posted by 930 porsche

Is it true that by going outside the left rear flare with a 3" steel pipe to the turbo charger will get better performance than going inside the engine like your picture shows?

930 porsche · 07-09-2009, 12:33 PM

I did try that with a 3" pipe with a HKS flange adapter on it. It took a lot of space and was leaking oil everytime the boost was on. I talked to HKS tech support and told me that the BOV had to be between the throttle body and the intercooler. Since the intercooler is sitting on the throttle body, then the location should be on the cold side of the intercooler which is the opposite side of the pipe from the turbo to the intercooler facing and looking straight at the back of the car. What do you think?

WERK I · WERK I's Garage

I like the idea of the BOV in between the throttle and the "cold" side of the IC output. The bov will last longer because it operates in a cooler environment. I have seen IC's with a bung welded on the cool side of the IC which the bov can mount to.

930 porsche · 07-09-2009, 12:57 PM

For the steel pipe from the intake going into the wheel well to the turbo charger was set up like this when I bought the car 5 years ago. I was just wandering if the air is getting a more even flow than going in through the engine department?

nreed · nreed's Garage

I placed mine between the turbo and intercooler. With my MCU setup, doing it this way provides a better throttle response. ie. the pressure sensor gets much less fluctuations and therefore the MCU is happier. Sure its a little hotter in that location but the BOV can take it.

A930Rocket · 07-09-2009, 06:08 PM

Is the BOV like the above an EFI only item? Would a CIS engine benefit from one?

nreed · nreed's Garage

It should work fine on a CIS. Much better than the original stock plastic one.

930 porsche · 07-09-2009, 07:42 PM

Greddy, HKS, etc.. are saying it should be placed between the intercooler and the throttle body. In our case for 930, on the cold side of the intercooler welded with a flange. Is it true?

930 porsche · 07-09-2009, 07:44 PM

By the way what is a MCU?

nreed · nreed's Garage

Sorry - MCU = Microcontroller unit - ECU = Engine control unit - I use the terms interchangably

911st · 07-10-2009, 06:58 AM

BOV or CBV can go anywhere after the turbo discharge and before the throttle body. It is preferred to put it as close to the TB as possible but many do not because of packaging needs.

I suspect having it closer to the TB allows faster recovery and closer to the turbo should reduce turbo shock / stall quicker.

On a CIS one should use a CBV style BOV, (compressor bypass valve) as air that has gone through the metering plate must not be vented to atmosphere or the motor will go fat. This can turn the turbine into a jet motor and or shoot even bigger flames.

The exit of the CBV needs to be plumbed back in after the air cleaner and before the Turbo intake.

On my C2 Turbo I revered my aftermarket slide type CBV and set it up so is was open at cruse and idle and only closed on accel. This gave me faster boost. With accel on the freeway I pulled instant .5 bar boost.

911st · 07-10-2009, 07:01 AM

Sorry, on a CIS the CBV exit needs to be plumbed in not just after the air filter but after the fuel metering assembly and before the turbo intake.

EFI can mostly be vented to atmosphere except not the best idea if it is a suck through style set up.

930 porsche · 07-10-2009, 08:34 AM

What is TB?

911st · 07-10-2009, 08:41 AM

Throttle Body

930 porsche · 07-10-2009, 08:45 AM

Where is the CBV on my 3.3?