BOV location

[puddy]

I've seen pics of Blow Off Valves attached directly to intercoolers. Mine is a plastic OEM version (i believe) in a 965 style intake elbow. I'll have my engine out over the winter doing an EFI conversion, is there any benefit to moving my BOV to my intercooler?

I think i'll be modifying my intake anyways after I eliminate the CIS system.

[philip j]

Originally Posted by puddy

I've seen pics of Blow Off Valves attached directly to intercoolers. Mine is a plastic OEM version (i believe) in a 965 style intake elbow. I'll have my engine out over the winter doing an EFI conversion, is there any benefit to moving my BOV to my intercooler?

I think i'll be modifying my intake anyways after I eliminate the CIS system.

Hey Chris, I use the same BOV and have it on my intercooler... as long as its between the turbo outlet/throttle body it will do the same function... Philip

[puddy]

Thanks Philip, any chance you can email me a picture of your BOV at some point as well as your air intake pipe?

[Tippy]

Originally Posted by philip j

Hey Chris, I use the same BOV and have it on my intercooler... as long as its between the turbo outlet/throttle body it will do the same function... Philip

Correct, but putting the blow off valve near the outlet of the turbo, close as possible aids boost recovery

[puddy]

OK thanks for the info!

[Mike Billings]

[quattrorunner]

Originally Posted by Mike Billings

That looks awesome but don’t you think the end tank on each side would be better if it had had a smoother transistion? Two 2” hoses running directly into the tubes and fins seem abrupt. I’m no engineer though.

[Mike Billings]

Very good points. Thanks for posting that. Tanks are a little small also. No air ducting etc. If you saw the manifold, I think similar comments.

Not looking for horsepower however. 1850 pounds!

[9dreizig]

Mindtrust... I just picked up a powerhaus intercooler that has the boV directly to atmosphere. Can I just instal it or do I need to disconnect and re-plumb the OEM BOV ? Any harm having two in the system ?

[T77911S]

one thing you want to check for if venting is if it is open at idle.
if so, it is an "air leak" and make it run lean at idle.
if it is open when at cruise speed it will run rich.

I don't think I would run 2.
I have left the one in the elbow there but removed the vac/boost hose to it when I installed one on the IC and vented it

['76 911S 3.0]

Originally Posted by Tippy

Correct, but putting the blow off valve near the outlet of the turbo, close as possible aids boost recovery

This^^^ I have mine mounted roughly 6" after the compressor outlet:

[Tippy]

That’s exactly where mine is. It’s tucked nicely where the dizzy used to be.

[matsuzaka]

Anyone not running a blow-off or bypass valve?

[Raceboy]

Originally Posted by matsuzaka

Anyone not running a blow-off or bypass valve?

Very bad for a turbo.

Other option would be to use second throttle pre-turbo like they did in 80's turbo era.

[matsuzaka]

I worked for 1G Racing in Ross, Ohio, US distributor of Noble cars about ten years ago. Noble cars were powered by a twin turbo Ford V6 and one of the distinguishing feature was that it did not have a bypass or blowoff valve.
I was aware of this before I went to work for 1G because I had read an article about the Noble. Around that time I had been working to build a turbo converted VW Corrado engine for my 92 GTi and one of the books I had studied was Corky Bell’s book Maximum Boost. People I talked to about eliminating bypass/blowoff said similar things like Raceboy above. One day I called Corky Bell and questioned him about this subject and what he told me is that there’s a lot of misinformation about this subject and that not having a valve is not detrimental to a turbo system. The primary reason factory cars use them is to eliminate the “chirping” noise that emanates from the turbo when you get out of the throttle, while shifting for example. The benefit being you don’t loose the boost in the system while you shift, and for a while Noble was faster to 60mph than any exotic on the market.
Although, I did end up using a blowoff valve on my GTi, it was primarily for the cool noise it made as you shifted, purely cosmetic, if you will. Some of the Noble customers did install blowoff valves for the same reason. I can also confirm that the Nobles do make a “chirping” noise Corky had mentioned but I did not think it was that bothersome.

[matsuzaka]

I worked for 1G Racing in Ross, Ohio, US distributor of Noble cars about ten years ago. Noble cars were powered by a twin turbo Ford V6 and one of the distinguishing feature was that it did not have a bypass or blowoff valve.
I was aware of this before I went to work for 1G because I had read an article about the Noble. Around that time I had been working to build a turbo converted VW Corrado engine for my 92 GTi and one of the books I had studied was Corky Bell’s book Maximum Boost. People I talked to about eliminating bypass/blowoff said similar things like Raceboy above. One day I called Corky Bell and questioned him about this subject and what he told me is that there’s a lot of misinformation about this subject and that not having a valve is not detrimental to a turbo system. The primary reason
factory cars use them is to eliminate the “chirping” noise that emanates from the turbo when you get out of the throttle, while shifting for example. The benefit being you don’t loose the boost in the system while you shift, and for a while Noble was faster to 60mph than any exotic on the market.
Although, I did end up using a blowoff valve on my GTi, it was primarily for the cool noise it made as you shifted, purely cosmetic, if you will. Some of the Noble customers did install blowoff valves for the same reason. I can also confirm that the Nobles do make a “chirping” noise Corky had mentioned but I did not think it was that bothersome.

[Speedy Squirrel]

Nope. We do it because it is slower without it in normal driving.

When you close the throttle, the pressure at the compressor outlet causes the turbo to slow its rotation. When you open the throttle back up, it has to spin back up again. With a compressor bypass, the turbo speed stays up, or even increases slightly. Higher speed = More boost.

In a sport like drag racing you can do things differently. You can shift with the throttle open, and let the rev limiter take care of the engine revs. In this case, the compressor bypass doesn’t make much difference.