BOV vs dump valve vs bypass?

[texaselite]

A few questions:

I have read about updating the Elan to increase turbo life. Just really confused by the current status vs what I need to do.

1) Can someone clarify the difference between a blow-off valve,dump valve, and bypass valve? The terms seem to be used interchangeably here.
2) What does the Fed Elan have on it stock (blow off, dump, bypass)?
3) If I don't mind the whoosh sound at all, what is my best bet for upgrade (ideally, something I can do on my own)? Does the upgrade require re-circulating the line back into the trash can? I am not going to change to open intake (k&n) - I've already got a K&N in the trash can and am ok with that.
4) Any reviews on the TurboXS Compressor bypass valve and Inlet pipe offered by Top End?. I like the idea of upgrading the inlet pipe...just not sure if the TurboXS Compressor "bypass" valve is the way to go.
5) Any other sources for the inlet pipe upgrade other than TopEnd?

[rip]

I'm not sure about a bypass valve (it may well be another name for one of the others), but a dump valve bleeds excess pressure over a certain value which should be set higher than max boost. A BOV bleeds pressure when it detects a difference across the throttle valve plate (if the throttle is open, this will be small & when closed, this will be high). Both are adjustable but I found no difference at all when I fiddled with the adjustment on my BOV.
The two perform the same function but as described above, are activated differently. IMO a BOV seems like a better solution.

If you want to pipe it back into the trash can, then you need a recirculating type of valve & this gets rid of the whoosh sound. If you want the whoosh, then an atmospheric valve is the one to go for. You can still pipe this away from the engine & through a mild filter to get rid of the whoosh sound if you like.

Stock Elans do not have a BOV or dump valve. As mentioned earlier, I do not know what a bypass valve is so cannot comment on that.

There used to be an intake pipe available known as 'Bills Isuzu intake pipe' . You may be able to find references to it on this forum but I am not sure if it is atill available.

[texaselite]

So what is the current "woosh" sound that I hear when turbo is engaged (and I lay off pedal)?

[norman lovie]

Without a Dump valve, the excess charge in the inlet when the throttle plate closes bleeds back through the turbo compressor and then to the compressor inlet i.e. the inlet air filter route
This is generally good for on/off/ on throttle response - but not mechanically good for the turbo because it can cause damaging effects on the compressor blades - a good example of this is a typical rally car where you hear turbo chatter when they lift off - it's ok for them work's drivers - they can afford new turbo's
you get away with it in the elan because of the relatively low turbo boost level's - but try it with say 1.5Bar and watch yir turbo die prematurely
so you hear this bleed back occurring
A crude dump valve, that is held closed by the boost pressure via a small hose tied into the plenum chamber down stream of the throttle plate - and it snap's open when the throttle plate is closed and the plenum goes into vacum - this quickly gets rid of the pressure build up without bleeding back through the compressor - but it can put a strain on the turbo thrust bearing and seals ( imagine the loads pushing one way during pressure build then slamming back the otherway when it quickly vents - this is what the thrust bearing has to put up with

A BOV is named for several purposes, one is like a dump valve but with a finer control, it will open - like a dump valve but in a more controlled manner - BOV is also used to describe a crude device you fit into the wastegate control line to crudly gain more boost or atleast a quicker boost response

leading to - what I imagine is otherwise called the by pass valve - this could be a reference to the waste gate - which is what regulates the amount of ex gas driving the turbine, when it opens it lets the ex gas by pass the turbine - this is used to control the boost on the way up - and the dump valve gets rid of the boost on the way down
an internal waste gate comes with the turbo, you can fit an external WG - which has some advantages - more specifically to a higher tuned turbo - seeing flames licking out the side of the front wing on highly tuned turbo track car's is the screamer pipe being fed by an external WG ( by pass valve) along with a good dose of unburnt fuel that they let into the ex manifold for various reasons - all very noisy and unsociable - -- - but fun

[tigerdog]

As others have said, the purpose of any such valve (regardless of what you call it) is to keep the turbocharger spinning when the throttle closes, i.e. when shifting. Without a valve, a reverse pressure wave is created when the throttle closes. This backpressure has the effect of stopping the spinning turbo. Back on the throttle and the turbo has to spin back up before you get back on the boost. With such a valve, boost pressure is vented (to atmosphere or back to the turbo intake side) and the turbo allowed to freewheel during the shift; boost comes on more quickly when you return to the throttle.

Names are just names:
Dump: "dump" the boost out of the intake, typically to atmosphere
Blow-off: "blow" the boost pressure "off" of the intake.
Bypass: "bypass" the compressor so boost is recirculated back into the intake side of the compressor

"Compressor Bypass Valve" seems to be a thought-out term for what a recirculating valve does. This post has links to a couple of pretty-well written articles that helped me understand what such a valve does.