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Discussion Starter · #1 ·
First off, this is not a question where it's about "which blow off valve to get because it makes the loudest sound" post.

I've been reading up and I'm trying to get an understanding of this stuff. I know the S60R/V70R utilizes a compressor bypass valve(CBV). Does anyone know anything specific about this particular valve?
How much boost is it capable of holding? Brand? Type? Does boost leak occur? How much boost is it capable of holding?

Also, in regards to the H valve. This is apparently the only valve that makes a performance difference. It increases low end torque (not that peak tq at 2500 isn't enough...) Has anyone had any experience with this valve, in terms of holding boost for too long and going into limp mode.

As for the blow off valve...
Screw the blow off, all it does is makes sounds. From what I've read (someone correct me if I'm wrong) CBV is the way to go with the way our injection system is designed.

awaiting blowoff/bypass enlightenment
 

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I just did a google on the H-valve, as I'm not up to speed on it. I found that the EVO and AUDI folks prefer it to the h-valve... I suppose it's "race" spec or something? This is ridiculous... will it even work on our cars?
 

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Re: Blowoff/Bypass/H Valve (Yin Lun)

Fact
Blow off valves are inferior to bypass valves because they dump air to the atmosphere. This air has already been metered by the mass airflow meter. As a result, errors are introduced into the air/fuel ratio calculations. There is no benefit to gained over a good bypass design.

Opinion
Blow off valves suck because they make stupid farting noises that are designed to draw attention to the driver (farter?). They have no place on a Volvo.

I don't know if the OEM CBV leaks, but I seriously doubt it.

Sometimes people will add a blow off valve with aftermarket turbo setups because a bypass is not available. In that case, something might be better than nothing.

If you plumb the outlet of a blow off valve to the compressor inlet duct, it becomes a "bypass".
 

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Re: (CyberDoberman)

OK... with your short note I assumed you were kidding...

But isn't the N75 series of valves actually wastegate actuators?
 

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Discussion Starter · #9 ·
Re: Blowoff/Bypass/H Valve (Dyno)

Quote, originally posted by Dyno »
Fact
Blow off valves are inferior to bypass valves because they dump air to the atmosphere. This air has already been metered by the mass airflow meter. As a result, errors are introduced into the air/fuel ratio calculations. There is no benefit to gained over a good bypass design.

Opinion
Blow off valves suck because they make stupid farting noises that are designed to draw attention to the driver (farter?). They have no place on a Volvo.

I don't know if the OEM CBV leaks, but I seriously doubt it.

Sometimes people will add a blow off valve with aftermarket turbo setups because a bypass is not available. In that case, something might be better than nothing.

If you plumb the outlet of a blow off valve to the compressor inlet duct, it becomes a "bypass".

Ahh..but on the flip side, that air has already been heated up by the turbo. If there was someway to get the same amount of air from a blow off, then the fresh air would be better.
 

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Re: Blowoff/Bypass/H Valve (Yin Lun)

No matter what, air must pass through the compressor on it's way to the engine.

Besides, BOV's and CBV's do their thing when you LIFT the throttle, so gaining/losing horsepower or temperature in that situation is not a concern.

Also, I suspect cbv's do a better job of keeping turbo shaft speed up when you lift between gears (delta P across the compressor probably less because you're "supercharging" the compressor inlet)
 

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Re: Blowoff/Bypass/H Valve (Dyno)

Quote, originally posted by Dyno »
No matter what, air must pass through the compressor on it's way to the engine.

Besides, BOV's and CBV's do their thing when you LIFT the throttle, so gaining/losing horsepower or temperature in that situation is not a concern.

Also, I suspect cbv's do a better job of keeping turbo shaft speed up when you lift between gears (delta P across the compressor probably less because you're "supercharging" the compressor inlet)
Hahahah! But then it goes to the IC for a cool down! Hahahahah!!! The CBV vents the charged air back into the intake. That charged air is supper hot! Not good! Also, you will only run rich with a BOV for a split second! Who cares! One other thing, why doesn't a BOV belong on a Volvo?
Because Volvos are sooo prestigious? Puhlease!

Modified by gdogg16 at 8:37 PM 9-9-2004
 

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Discussion Starter · #13 ·
Re: (gdogg16)

Quote, originally posted by gdogg16 »

Yes, the N75H and the N75J are both wastgate actuators.

care to elaborate more on that?
 

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Re: (gdogg16)

Another thread down the tubes. Happening quicker and quicker, it seems. Too bad. Could have been a useful one.
 

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Re: (Dyno)

Quote, originally posted by Dyno »
Another thread down the tubes. Happening quicker and quicker, it seems. Too bad. Could have been a useful one.
Still is! Just some people don't know what they are talking about. The reason I didn't elaborate on the N75J, is because there isn't anything to elaborate on. It's a wastegate actuator, if one doesn't know what that is, I suggest a search.
 

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Discussion Starter · #18 ·
Re: (gdogg16)

I'll do my search....(unfortunately I know nothing of turbos)

but what are the difference between the two? pros/cons?
 

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Re: (Yin Lun)

Quote, originally posted by Yin Lun »
I'll do my search....(unfortunately I know nothing of turbos)

but what are the difference between the two? pros/cons?
The diaphrams are slightly different and they are upgrades to the stock N75 on VW's and such. When running more boost the N75 causes huge boost spikes and leaks. So to correct this, they have upgraded to either the H or the J. Some like the H over the J and vis versa.
 
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