Back To BOV

[Stuart]

Reading all that has been said about BOV

[mike_sekinger]

Reading all that has been said about BOV

Edited October 12, 2005 by mike_sekinger

[superdavelotus]

That's right Mike, The PNM has everything needed to get you up and running apart from the tools to fit it of course!

I think you get

2 x silicone tee-pieces

4 x large jubilee clips

2 x smaller jubilee clips

1 x 5mm nylon tee piece or Y piece

1 x 750mm long silicone hose

Hope this helps,

Dave

[mike_sekinger]

That's right Mike, The PNM has everything needed to get you up and running apart from the tools to fit it of course!

I think you get

2 x silicone tee-pieces

4 x large jubilee clips

2 x smaller jubilee clips

1 x 5mm nylon tee piece or Y piece

1 x 750mm long silicone hose

<{POST_SNAPBACK}>

wot no BOVs?..... hopefully you get a couple of BOVs as well?....

[superdavelotus]

NO they're extra LOL! Only joking, good job one of us is on the ball Mike. Just testing to see if anyone was actually taking any notice of these threads on this forum.

[hovgaard]

You may want to read my dump valve mod in the garage for my humble opinion on the subject. I may only run 4 cylinders, but the principle is the same.

I don't own a V8, so I don't know if it has compressor bypass valves built into the compressor housings or anything like that. But, summing up, what I'm saying is:

1: If it already has such valves, stay stock.

2: Never open directly to the atmosphere if you care about engine longevity (unless you put a good airfilter on your valve (in which case it would seem easier to run a pipe to the compressor intake!)).

Now flame me...

Cheers!

Edited October 18, 2005 by hovgaard

[Phil_B]

This starts to add some meat to my confusion. I used to have a Fiat Coupe 20V turbo, and on this I replaced the standard Bosch dump valve with an uprated one (forge motorsport version). This was mainly for longivity of the turbo, and to make things smoother through the gears (which it did - very nicely). Like for like these were both recirculating, and I can see how these would work feeding pressure back to the intake to keep the turbo spooling, rather than slamming them off when the load is removed. However blow off valve just means dump to air (hence you will get a big woosh, for instance when changing gear yes?). If there is any leak, won't this cause the ECU problems? What is the advantage over a recirc, is it just the speed of operation (ie less resistence and hence better and quicker protection). Why are these things never put on turbo charged cars as standard.

The lack of my knowledge knows no bounds!

Phil B

[hovgaard]

Phil - was that Bosch valve the same as the one I have used on the S4? If so, was there *really* any difference felt when installing the Forge valve? If so, what exactly? I am much pleased with my cheapo fix.

When it comes to confusing the ECU, here is the deal. On engines that have an air mass meter (AMM for short), yes it gets confused over leaks or dump valves opening into the atmosphere, because the metered amount of air is not what actually enters the combustion chambers. If the difference is small, the lambda sensor will help correct the situation, but if the difference is big it may lead to erratic engine operation, like puffs of smoke when suddenly dumping much air or running lean and hot if sucking air through leaks. A recirculating valve would seem essential to all but the boy racer.

However, our Esprits don't have AMMs. The Esprit ECU relies instead on the manifold absolute pressure sensor (MAP for short). This measures the air pressure in the intake manifold, and that allows the ECU to calculate the airflow going into the combustion chambers. Such a system is harder to confuse with leaks or aftermarket valves, and valves dumping into the atmosphere for the sake of sound are acceptable from an ECU standpoint. I would still argue that they are unsafe in an air filtration perspective and offer inferior performance to the compressor bypass valve setup that I have made.

MAP systems tend to have quicker response times and feel crisper and don't get suckered by leaks, AMM systems are easier to deal with when tuning at home because it automatically registers resulting the changes in airflow.

No consumer car gasoline engine know to mankind (or to me) has both the AMM and the MAP.

And by the way - the WHOOOSH noise is SO pass

[Htown]

Phil - was that Bosch valve the same as the one I have used on the S4? If so, was there *really* any difference felt when installing the Forge valve? If so, what exactly? I am much pleased with my cheapo fix.

When it comes to confusing the ECU, here is the deal. On engines that have an air mass meter (AMM for short), yes it gets confused over leaks or dump valves opening into the atmosphere, because the metered amount of air is not what actually enters the combustion chambers. If the difference is small, the lambda sensor will help correct the situation, but if the difference is big it may lead to erratic engine operation, like puffs of smoke when suddenly dumping much air or running lean and hot if sucking air through leaks. A recirculating valve would seem essential to all but the boy racer.

However, our Esprits don't have AMMs. The Esprit ECU relies instead on the manifold absolute pressure sensor (MAP for short). This measures the air pressure in the intake manifold, and that allows the ECU to calculate the airflow going into the combustion chambers. Such a system is harder to confuse with leaks or aftermarket valves, and valves dumping into the atmosphere for the sake of sound are acceptable from an ECU standpoint. I would still argue that they are unsafe in an air filtration perspective and offer inferior performance to the compressor bypass valve setup that I have made.

MAP systems tend to have quicker response times and feel crisper and don't get suckered by leaks, AMM systems are easier to deal with when tuning at home because it automatically registers resulting the changes in airflow.

No consumer car gasoline engine know to mankind (or to me) has both the AMM and the MAP.

And by the way - the WHOOOSH noise is SO pass

[hovgaard]

I'm not actually bothered by noises as such, but as I'm doing it the recirculating way (as I believe that to provide the best performance), there isn't very much noise from my valve at all, regardless of it being close to the compressor. It's certainly at lot quieter that the stock surge noise.

I realise that I'm taking a gamble on valve durability here, but it still looks good as new (recently checked). I feel that I can subscribe to Bosch valves if needs be and it would still come to less money than a single 'good' one. No signs of wear yet, though.

This reaction time due to valve location - I don't understand. My valve is actuated by the vacuum after the throttles (it T'd off the MAP sensor hose), and it would be actuated that way regardless of where I put it.

If I was to locate the valve after the charge air cooler, in an effort to improve its reaction time, I'd be putting heat into the charge air cooler during gear changes which I don't want to do, while at the same time the air density in my compressor housing would increase, exerting a larger braking torque on the compressor wheel which I don't want either.

In what way does valve reaction time change on grounds of its location? And could that ever make up for the effects I'm describing?

[Htown]

hovgaard wrote:

I'm not actually bothered by noises as such, but as I'm doing it the recirculating way (as I believe that to provide the best performance), there isn't very much noise from my valve at all, regardless of it being close to the compressor. It's certainly at lot quieter that the stock surge noise.

-----I realize that your setup is probably silent, I was just refering to the effects

of vent to atmosphere valves when installed near the turbo.-------

I realise that I'm taking a gamble on valve durability here, but it still looks good as new (recently checked). I feel that I can subscribe to Bosch valves if needs be and it would still come to less money than a single 'good' one. No signs of wear yet, though.

-----Just something to watch out for, that's all. My Forge Motorsport recriculating

valve on my audi S4 does get affected by radiant heat from being in such

close proximity to the turbo---------

This reaction time due to valve location - I don't understand. My valve is actuated by the vacuum after the throttles (it T'd off the MAP sensor hose), and it would be actuated that way regardless of where I put it.

------Not neccessarily, your valve is actuated by a pressure differential, not just

vacuum. Placing the valve post intercooler means there will always be

intercooled air ready to rush back towards the throttle plates.

If you place the BOV before the intercooler, what happens is the

compressed air is vented out before the intercooler, leaving an 'air pocket'

in the intake and intercooler. When you open your throttle again, it takes

time for the intercooler and intake tract to fill up with air again, therfore

creating an increase in 'lag time'. Placing the bov or bpv post intercooler

(or closer to the throttle plates) ensures a quicker 'response'. There are

many tests posted online that can better describe it than I can though.

Search around.----------

If I was to locate the valve after the charge air cooler, in an effort to improve its reaction time, I'd be putting heat into the charge air cooler during gear changes which I don't want to do, while at the same time the air density in my compressor housing would increase, exerting a larger braking torque on the compressor wheel which I don't want either.

----The pressure is being 'released' by the valve regardless of it's location,

along with the heat by-product. One valve location won't 'heat' the air

more than another. It is the 'refilling' of the area that makes a difference

in reaction time.-------

In what way does valve reaction time change on grounds of its location? And could that ever make up for the effects I'm describing?

-----Look at every single valve manufacture's website. They all recommend

fitment closer to the throttle plates versus placement near the turbo. The

pressure from shutting the throttle builds up in the plenum and intercooler

in a 'wave', starting at the throttle plates, and working it's way back toward

the source of pressure (turbo). The 'sooner' you can relieve that pressure

(as close to the throttle plates as possible) the faster the response of the

valve.-------

Edited October 20, 2005 by Htown

[Phil_B]

Phil - was that Bosch valve the same as the one I have used on the S4? If so, was there *really* any difference felt when installing the Forge valve? If so, what exactly? I am much pleased with my cheapo fix.

<{POST_SNAPBACK}>

Certainly on my Fiat it make a real difference. I was surprised myself. I had read up about the various options, and it was the only Mod I made to the car in the three years I had it. I didn't expect to feel any difference at all, but I was wrong. The difference it made was mainly in the smoothness through the gears when under hard acceleration, but to be honest it was noticable even in normal driving (I'm not really a boy racer). When I sold the fiat, I put the old Bosch one back on and sold the DV006 to a chap here at work with a Saab 9-5 Aero with the same Bosch unit, and he said just the same. No performance increase observed, but certainly much smoother delivery through gears. He was quite a good mechanic, having raced a track day car for a number of years, and we tried to work out why it should make a difference. I guess better engineering parts mean that the resistence is lower, and so it kicks in that much quicker, meaning that the turbo really does stay spooled up better, resulting in a smoother transition.

Thanks for the detail on the AMM. Yes this was the system that the Fiat ran. I remember now a lot of the conversation on the Fiat Coupe Forum centred around this. Interesting.

Phil B

[hovgaard]

Phil - Could it be that the Forge valve turns out to have lower internal air resistance when open than does the Bosch ditto or something like that? I must say that intrigues me. If that is to be confirmed I might be tempted to try it , although I find it pricey.

Htown - respectfully I disagree with you on a number of points.

The overall goal here should be to maintain maximum turbocharger RPM during gearchanges, since that is the overriding factor determining how much power we make immediately after a gearchange. The only effective, readily available, cheap way to do that is to minimise air density in the compressor housing. Air density is not only determined by pressure but also by temperature.

1: The best way to do it is to put an extra throttle valve before the compressor intake. This is what they did in the good old days of F1 . They also had ordinary throttles like we do, and complex linkages or control mechanisms between the main throttles and the one on the compressor intake. This way the engine quickly eats up all the air in the entire charge air system, and with vacuum in the compressor housing virtually no braking torque is exerted on the compressor wheel. I have friends who have tried this on a motorcycle project (using only a throttle on the compressor intake and no main ones) and they say that, since the engine is still good for a few puffs of smoke just after you close the throttle, turbo RPM actually goes up a bit and then just stays there during shifts. With high turbo RPM available after the gearchange, the charge air system fills up quickly, and response was found to be far superior to any other setup, confirming why the did it in F1. Kids, don't try this at home. Your standard turbocharger oil seals were not designed for vacuum in the compressor housing and will fail, leading to oil contamination in the charge air system.

2: The second best way to do it is how it is done by most - if not all - major turbocharger manufacturers. They offer compressor housings with built in compressor bypass valves. During a gearchange, the same air is pumped round and round in the compressor housing, heating it up slightly which will reduce its density and thus reduce the brake torque it can exert on the compressor wheel. Incidentally, that also takes the heat load off the charge air cooler, which is allowed to cool down a bit. This is how it works in the vast majority of gasoline turbo car engines out there, and it is what I emulate with my setup. Why Lotus didn't do it, I don't know. I have tried asking my acquaintances at Garrett, but gotten no clear answer. Cost, most likely.

If one was to do what I do, but with the valve located after the charge air cooler, the air temperature would not be allowed to increase in the compressor housing as the air would be cooled every time it passed through the charge air cooler, and performance would suffer as a result.

3: The third best way is to blow off air into the atmosphere, any valve location will do. This way the compressor is operating at atmospheric density. The reason that aftermarket valve manufacturers invariably will recommend that we put their stuff well away from the turbo, I suspect to be that they don't want to risk that someone somewhere puts their valve directly exposed to exhaust manifold heat radiation. Not having valves fail is their priority as it would give them a bad name. Obviously they don't care about things like air filtration and the like. But it could also be that having the valve close to the throttles maintains gas speed momentum in as large a portion of the charge air system as possible, which would be a benefit when opening the throttles again, though it could never compete with having a higher turbo speed available after the gearchange. I will readily admit that #2 is not far superior to #3 merely in a turbo RPM perspective, but it is superior all the same. Factor in air filtration, and the choice should be clear.

4: The fourth best (and worst) way is to do nothing at all. That is what Lotus did to my car when they built it, and it results in severe compressor surge. The air density in the compressor housing cycles back and forth between atmospheric conditions and boost pressure, and is the most effective way to reduce turbo RPM I can think of in this context. It also minimises compressor life, as the wheel will fatigue.

That all applied to compressor conditioning, which I believe to be the topic here. There are other ways of making the turbo spin, like pumping air and fuel into the exhaust manifold, or putting an electric motor in the bearing housing, but I think that is another discussion.

Cheers!

[Htown]

Htown - respectfully I disagree with you on a number of points.

<{POST_SNAPBACK}>

Hehe, me too.

though I think we may be talking about different (but related) response times. I'm talking about how fast the valve reacts, not neccessarily 'turbo-lag'. Obviously, a diverter or bov is better than the stock setup, regardless of location. Just trying to point out the advantages of certain valve placement versus another.

Yet the question still remains....If the valve placement near the turbo offers all of these great benefits, then why do manufactures recommend placement closer to the throttle body? I have to trust the experts here.

Regards,

Craig

[hovgaard]

Craig, -

Like I said, I think they feel more comfortable well away from exhaust manifold heat.

And, if we talk about valves that blow off into the atmosphere, I'm not so sure what location is best. Put it on the compressor discharge, and you will have no heat load on the charge air cooler, allowing it to chill out during shifts. Put it close to the throttles and you maintain gas momentum throughout the charge air system during shifts. I don't know which is better, I have no real experience with this type of valve, as I don't like them.

It is the recirculating valve that I'm convinced should sit on the compressor discharge, to minimize air density in the compressor housing during shifts.

Hope that clarifies my view, although maybe it didn't fully answer your question.

Edited October 20, 2005 by hovgaard

[Htown]

Craig, -

Like I said, I think they feel more comfortable well away from exhaust manifold heat.

And, if we talk about valves that blow off into the atmosphere, I'm not so sure what location is best. Put it on the compressor discharge, and you will have no heat load on the charge air cooler, allowing it to chill out during shifts. Put it close to the throttles and you maintain gas momentum throughout the charge air system during shifts. I don't know which is better.

It is the recirculating valve that I'm convinced should sit on the compressor discharge, to minimize air density in the compressor housing during shifts.

Hope that clarifies my view, although maybe it didn't fully answer your question.

<{POST_SNAPBACK}>

Gotcha-

Edited October 20, 2005 by Htown

[hovgaard]

I pour my wisdom into the www, and yet it ends up Craig: 1 - Jens: 0. It's not fair, this life.

Next they will be asking who shot JFK and what's the meaning of life.

Anyway, it doesn't matter if we don't know where to put BOVs, my setup is better regardless. B)

Edited October 20, 2005 by hovgaard

[Htown]

I pour my wisdom into the www, and yet it ends up Craig: 1 - Jens: 0. It's not fair, this life.

Next they will be asking who shot JFK and what's the meaning of life.

Anyway, it doesn't matter if we don't know where to put BOVs, my setup is better regardless.  B)

<{POST_SNAPBACK}>

No, no, no "Gotcha" in real english 'the American' kind is slang for "i understand"

[hovgaard]

Ah, that kinda gotcha. Around here, it's what you say when you remove acne. Either way (that's 'ether way' to you Craig), it's been nice talking.

[Htown]

Ah, that kinda gotcha. Around here, it's what you say when you remove acne. Either way (that's 'ether way' to you Craig), it's been nice talking.

<{POST_SNAPBACK}>

LOL! likewise-

[mchlrodrigues]

Guys,

The main reason the use a dump valve over a recirculating one is it simplifies one's plumbing. I had an HKS "race" blow off/recirculation valve before the present TiAL valve. Venting the pressurized air into the compressor inlet tube (granted, mine is aluminum) made just as much noise as the dump valve.

Locating the valve near the butterflies vents the pressure at the location of the obstruction while keeping the system charged for the best possible throttle response. The need to weld on a fitting keeps most people front locating the valve where it should be.

The considerations for valve selection should be quality of construction, capacity (mass/time) of air flow and responsiveness. Piston type valves, by the nature of their very design, have some friction between the piston and cylinder wall. That's not to say I wouldn't use one; they're often the most practical repalcement for a Bosch type valve, but they are suboptimal.

[hovgaard]

You may very well be correct in saying that the BOV should be located close to the throttles for best response when the throttles are reopened. I can neither confirm nor deny.

I chose not to use a BOV, instead I use a recirculation valve because it's:

* Better performance (at least in principle)

* Safe in air filtration

I may not have used the best valve out there, so it is quite possible that you can get better performance with a really good BOV than I have with my cheap fix. At least I can say that my valve is the best value for money there is!

Anyway, welding on the inlet manifold isn't most peoples idea of 'simplified plumbing'!

I take it you don't have fuel injection, right? Because if you did, I suspect that, with that valve location, a bit of fuel from the secondary nozzles would collect in the valve and come out during gearchanges. Dangerous stuff!

[Jonathan]

Makes an interesting read (if you're into that kinda stuff )

BOV is the next mod I have to do on my car, I am probably going to go with a pre made system which taps off just after the intercooler as the prime reason for installing it is to reduce the strain on the turbo.

I must admit that feeding the air back into the system sounds optimal but I am a little concerned about the likelyhood of something breaking and then getting pushed back into the compressor housing.

Those that have done re-circs can you show me the details of how it's routed back to the airbox, I think I have it sorted but I am wondering if it is safe to feed the re-circ air -before- the filter or will it damage it ?

If anyone has any pictures etc I would be interested in seeing them.

[hovgaard]

I don't actually put it into the airbox itself. On the compressor intake I have an aluminium T pipe (suitable pipes are available from demon tweeks), that I put the air into. Sits on the compressor with a very short silicone hose. The big black hose from the airbox sits on the T pipe without being shortened, so reverting to stock is very simple. And, finally, I have a smaller silicone hose from the valve to the T-pipe.

Feeding the air back upstream of the airfilter is probably safe on the airfilter itself, but it defeats half the purpose of recirculation, i.e. making certain that the engine only ever gets filtered air.

Edited October 23, 2005 by hovgaard

[x6gas]

You may very well be correct in saying that the BOV should be located close to the throttles for best response when the throttles are reopened. I can neither confirm nor deny.

I chose not to use a BOV, instead I use a recirculation valve because it's:

* Better performance (at least in principle)

* Safe in air filtration

I may not have used the best valve out there, so it is quite possible that you can get better performance with a really good BOV than I have with my cheap fix. At least I can say that my valve is the best value for money there is!

Anyway, welding on the inlet manifold isn't most peoples idea of 'simplified plumbing'!

I take it you don't have fuel injection, right? Because if you did, I suspect that, with that valve location, a bit of fuel from the secondary nozzles would collect in the valve and come out during gearchanges. Dangerous stuff!

<{POST_SNAPBACK}>

Jens - did I miss something, but could describe exactly how your system works, what parts you need and maybe some photos? I am interested in copying your mod on my 4 pot S4.