Boost v BOV

[pcuser51]

:) Guys a question if you are running say 14psi of boost on your turbo does the BOV have to run the same :?: and if so why

[Cam]

What do you mean by does the BOV have to run the same?
do you mean the spring in the BOV?
Most BOV's are adjustable so you can adjust them to exactly the right spot for how the engine is set up

[Alspos]

A blow off valve is just that, a valve. It must be able to withstand 14psi of pressure (or whatever you're running) against it and not leak if it is to work effectively.
It just vents boosted air off when you change gears and in doing so helps keep turbo spooling. That is the theory. no doubt the debate will start from here on.....

[Jesusdroveawestfield]

I run 20psi plus and no Bov. I took it off as I hated the noise and felt it was too ricey.

[NXTIME]

I have the choice of either running a BOV an having a huge WOOSH sound, or not running one and having an even louder-sounding turbo flutter noise. How have you stopped the sound without a BOV, Daz?

[Project2501]

One word: Recirculate. I too am deadly sick of the flutter.. good for novelty value but annoying after the 2nd hour.

cheers

tom.

[NXTIME]

The only problem with recirculation is that hotter air is then put back into the turbo intake to be compressed and heated again. So the options are, WOOSH, FLUTTER or hotter air into turbo.

Damn, can't win.

[Project2501]

true.. but im hoping my cooler can handle the excess heat. It gets pretty cold on the outlet side.

cheers

tom.

[Will]

My understanding is that the flutter noise is the turbo cavitating which adds extra stress to the turbo. A lot of later model factory cars (e.g. 200SX) use a Bosch BOV which recirculates which is pretty quiet.

[CussCuss]

yes the flutter sound is the air going back through the blades of the turbo, as cool as it is, a recirculating BOV is the best method, doubly so on cars that still use an AFM.

[Will]

The only problem with recirculation is that hotter air is then put back into the turbo intake to be compressed and heated again.

Thinking about this further, the air being recirculated through a recirculating BOV won't get that much hotter since the turbo won't be compressing the air much at all. That is, the pressure at the outlet of the turbo while the BOV is open will be very low compared to full boost, which according to the laws of thermodynamics, means it shouldn't heat very much. The BOV will be opened mostly by the vaccum from the manifold side, so the pressure before the throttle plate will only be a few psi. So you're correct in that you are recirculating hotter and hotter air, but in practice, the effect shouldn't make the air too much hotter.

[NXTIME]

Thinking about the three options, the recirculating one woiuld probably be the best one. Will, you are correct, the compressed air - if vented post-intercooler - wont be as hot as the air pre-cooler. However, if it was hotter than the cold(er) air in the turbo intake then it will still stand to be detrimental to the overall intake temp.

Having said this, I really don't think that in the spilt-second time frame that gear changes occur (under competeive conditions) that it really matters all that much. I will recirculate the BOV and that will be that, or I can always use my right foot to stifle the sound by either not lifting off the throttle completely or doing so gradually.

[Will]

NXTIME, I think we're all in agreeance(?) that the recirculate option is the best compromise for noise and performance (keeping turbo spooled up between gears) and a requirement for AFM cars if the mixtures aren't to be disturbed. However, the main point I was trying to make was that without a significant increase in pressure, you get next to no temperature rise. To say it another way, the air doesn't heat up just becuase it goes past the turbine blades, although this might contribute a small amount of heat too. Seeing as this is a techincal forum, I'll launch into it:

Here's the equation for an ideal gas: pV = nRT

p = pressure
V = volume
n = number of moles of gas
R = universal gas _constant_
T = temperature

So if p goes up and everything else stays much the same, then T must go up unless we start breaking the laws of physics. I know that 'n' goes up too, but its at a rate slow enough that 'T' usually must rise too. Imagine pumping gas into a gas bottle. It usually heats up right? Similarly when you let the gas back out again, it cools the bottle.

This doesn't mean that you will get no temperature rise as you have rightly pointed out, but just to show how little it should increase as the turbo is blowing straight through the BOV when doing a gear change for example. So even if no intercooler was involved, it should still be OK to recirculate the air with minimal temperature increase as there is minimal pressure increase.

I think I strayed off topic a bit here, but thought this might be of some interest. I'm also applying ideal gas laws to a dynamic system, so there is a chance that there is a flaw in my arguement, so feel free to point it out to me if there is.

[pcuser51]

Guys a question if you are running say 14psi of boost on your turbo does the BOV have to run the same and if so why

:?: Mabe i can have another go at this: if your wastegate opens at 14psi does your BOV recirculate or not (this does not matter) have to open at
14psi and if it has to why :?:

[Project2501]

if your wastegate opens at 14psi does your BOV recirculate or not

?? If your wastegate opens at 14psi (max boost) then the BOV will still stay SHUT until you let go of the throttle. That is how the valve works. A bov doesnt regulate your boost, the wastegate does.

cheers

tom.