Bov/dv

[gareth_oau]

I was curious about the function of, and the differences between Blow-Off Valves and Diverter Valves. found this link
http://jsalmi.com/bov/
The author states they are the same, just a different name.

However, he did indicate that venting to atmosphere will cause a car to run rich, which is bad.

any views on that?


QUOTE
A BOV and a DV more or less the same, and perform the same function. The difference in terminology is pretty much meaningless. Where people get their undies in a bundle and/or burned is the issue about venting to atmosphere or not.
With a closed, MAF-based system (such as my current motor, a 1.8 litre turbocharged Audi), venting to atmosphere will cause the motor to run rich. Period. Venting a BOV/DV to atmosphere simply to make more noise is one of a number of definitions which puts the owner of that car into the category of "ricer". ( flames > /dev/null )

The ECU meters incoming air via the MAF, and using inputs from the MAF, TPS, MAP (if so equipped), RPM, O2 sensor(s) and who knows what else determines how long to fire the injectors. If any of that metered volume of air is vented to atmosphere, the ECU has no idea that it's lost some air and will fire the injectors long enough to match the volume or pre-metered air. Result? Rich condition.

And just for a minute, consider what happens a non-recirculated valve is open during normal driving. When not making boost, turbocharged motors live in vacuum. Maybe even enough vacuum to hold the BOV/DV open. Ingesting unmetered, and in 99% of the cases which I've seen, unfiltered air. Sound like a good idea?

Some BOVs are engineered to only vent to atmos, some are engineered to recirculate the vented charge. Look here for a picture of 2 valves sitting side by side. One is vent to atmos only, the other is designed to recirculate. Are the BOVs? Are they DVs? Does it really make any difference? (They are BOVs, for what it's worth...)

This BOV is what came stock on my 1995 twin turbo Toyota Supra. And this HKS Racing BOV is what replaced it when the supra was converted to a big single turbo. The supra was also converted from MAF-based to speed density, so venting this guy to atmosphere was OK. ( That motor made around 730 hp at the crank, with a bad tune (mine), after the mods which were done to it. On a 100% stock longblock. )

This DV comes stock on the TT porsche motors, and is also an upgrade to the OEM Audi/VW 1.8t valve. The part number is "0 280 142 110", and it's referred to as the "110" valve. It is the valve which is currently being used on my A4 1.8t motor. It begins to open at 4 inches of mercury worth of vacuum, and is fully opened at 8.5 in HG. Sorry for the blurry pictures, but my digicam doesn't do good closeups. ( The 1.8t motor made 150 crank hp stock, and is currently making around 200 crank HP. )

This Greddy "Type S" BOV is sitting on my bench, and will ultimately end up on my car. I'm missing the "flange eliminator" which bolts up to the bottom of the valve body. Geez - look at that - it recirculates too!

And finally, here is a Sard BOV which I had on my 1993 Mitsubishi Eclipse GSX. As you can see, it's designed to only vent to atmosphere. This motor was converted from MAF to speed density, so venting in this case was also OK. ( That motor made around 450 hp after the mods which were done to it, on a 100% stock longblock. )

Ok. With that out of the way.

As was stated abuve, DVs and BOVs are in essence the same. It's simply the nomenclature which is different. They both perform the same function, which is to protect the compressor from 'bad things' when the throttle plate snaps shut during the creation of boost pressure.

The charge in the IC plumbing can travel well in excess of 100 mph, and when the throttle plate closes the charge has nowhere to go. A shockwave can bounce off of the throttle plate and travel back through the IC plumbing to the compressor, and if the impact is great enough can stall the compressor, or perhaps even spin it backwards. Which is 'a bad thing' as far as the health of your turbocharger goes. The wheels are spinning anywhere between 100k and 200k RPM. From 100k to 0 rpm in an instant? No thanks.

The BOVs open when presented with some specific measure of vacuum. Vacuum is produced immediately in the intake manifold when the throttle plate shuts, so as soon as the BOV "sees" whatever level of vacuum is required, (say 10 inches of mercury, for example) it opens and some of the compressed charge is vented out of the IC plumbing and back into the intake stream - between the MAF and the compressor. This venting is what protects the turbocharger.

So - use a valve which recirculates the vented charge, unless you've done a speed density conversion or are using a blow-through MAF, which sits in the IC plumbing, somewhere between the compressor and the throttle body. A blow through MAF is most likely in the IC plumbing just before the TB. ( FWIW, the motor pictured in the blow thru MAF image is a 500+ awhp 4g63 1g DSM motor. )

Even these so-called "hybrid" valves - they still cause you to lose some of your pre-metered air. So why even bother with them? People think that the valves are analagous to the OEM valves (which recirculate 100% of the charge), while in fact they are not. Venting any of your pre-metered intake charge to atmosphere isn't the smartest thing to do.

If you gotta have noise, search Ebay for a "Blow Off Valve Simulator". That should do the trick.
UNQUOTE

[Preen59]

Well..

A diverter valve re-directs the excess inlet air back into the inlet prior to the compressor (and after the MAF) and therefor there is no airloss, meaning that the amount of air measured by the MAF sensor is the exact amount of air passing into the engine.

A blow-off valve simply vents the excess boost air to atmosphere, ie out into the open.



SO, basically, (theoretically here, exagerated) if the engine needs 12 parts air to one fuel (or 12:1), and it thinks it is getting 24 parts air, but its actually getting 18 parts air (because it has vented some of that air to atmosphere via the BOV without knowing it), that means that it will supply 2 parts fuel, when it actually needs 1.5 parts fuel.

This means that you are getting an air/fuel ratio of 9:1, instead of the theoretically ideal 12:1, so you are getting too much fuel for the amount of air in the charge, so it's a rich charge.

A blow off valve and a diverter valve perform the same function, but in a different way. They both are there to dump the boost when the inlet shuts and allow the turbo to continue to spin, reducing lag. Either perform the job equally well, its just a case of how your engine management works. Also, Diverter valves are used on production engines because any air that has (theoretically) come into contact with fuel must pass through the catilitic converter before it reaches the atmosphere. (which is a wank in my oppinion).

Hows that?

[gareth_oau]

so in essence, it looks like you agree (apart from the nomenclature). i'm presuming that running rich is not a good thing, kinda defeats the purpose of the turbo in the first place?

[Preen59]

so in essence, it looks like you agree (apart from the nomenclature). i'm presuming that running rich is not a good thing, kinda defeats the purpose of the turbo in the first place?

Yep, pretty much, just cleared it up a bit for you.

No, running rich doesn't defeat the purpose of the turbocharger, you are still creating boost and are still burning a larger charge, but because there is too much fuel in it, the charge will burn slowly and all of it will not burn, so you end up with sooty internals and plugs, plus an increase in fuel consumption and a decrease in performance.

[NeuSpeedGTI]

This is for a non-turbo 8v 1.8.. however what is recomended air/fuel ratios?

[fintelboss]

Yep that article looks good to me,

The reason people use blow off valves instead of diverter valves is because if they are chasing max power and are running a very high boost, it doesnt really matter if you get the occasionaly rich mixture - its better then the alternative of overboosting the engine, especialy on overrun, as venting to atmosphere is typicaly a lot quicker acting then recirculating diverter valves.

Since they are the best option for high power cars ie race/drift/drag it has become cool for everyone to get one. But they are not the best option for a normal street car with less then 100kw/h and police to deal with.

[Oneofthegreats]

This is for a non-turbo 8v 1.8.. however what is recomended air/fuel ratios?

The following is only described for standard issue fuel/gasoline.

No exotic fuels eg Nitro, Methanol, C14/16, avgas, Sunoco blends etc.

Just fuel straight from the service station.

The ideal or "stoichiometric" air/fuel ratio is 14.7:1 where there is just enough air to burn all the fuel.
Its also described as Lambda = 1.

Little trick for you all.
If you measure the oxygen sensor in your car with it disconnected, the exhaust gas creates a voltage in the sensor, which if it running at the ideal 14.7:1, the voltage will be approx 0.5V. If its rich it will have a high reading eg. 0.8V, if its lean, there voltage will be little or no voltage. eg. 1.2V



In NA form I set my K-Jet cars up at approx. 2.0% or around the 14.5:1 which seems to provide adequate power & fuel ecomony.

A few of my friends normally setup V8's around the mid-high 12's:1 & the same goes for tuned V8's eg. head & cammed up LSX engines

I like to setup FI (turbo/supercharged) at around the 12.2-12.5: to be on the safe side & is mostly the place where they make the most power.
Most tuners seem to set there A/F ratios up around the same for FI applications.


Although, fueling is only one part of the equation. The other being ignition timing plays just as an important roll as fuel & if your timing isn't right you could still blow your engine up even if the fueling is spot on!