Lucas Posted July 31, 2006 Share Posted July 31, 2006 I was chatting to a mate of mine this weekend and he said he was on the skyline forum talking about new parts he wants for his motor one of which was a dump value. He got a load of posts back saying they are really bad for the turbo. Now i am not a technical person and he did explain it to me but not sure i got it. So my question is are they bad and if so why? Link to comment Share on other sites More sharing options...
fredm Posted July 31, 2006 Share Posted July 31, 2006 http://www.max-boost.co.uk/max-boost/intake/DV.htm The above link (if I have done it right) makes interesting reading, as does the whole site. Link to comment Share on other sites More sharing options...
mikeyb10supra Posted July 31, 2006 Share Posted July 31, 2006 I was chatting to a mate of mine this weekend and he said he was on the skyline forum talking about new parts he wants for his motor one of which was a dump value. He got a load of posts back saying they are really bad for the turbo. Now i am not a technical person and he did explain it to me but not sure i got it. So my question is are they bad and if so why? he sounds like a bit of a pleb.....UK spec cars dont like em as it reeks havoc with Air Flow sensor and can cause rough idle and often the engine stalling, they release compression surge into the atmosphere so there is no way of it backing up into the turbo housing and possibly shattering it stock supras are fitted with a recirculating type valve and these are ok, so I cant see the problem with venting to the atmosphere Link to comment Share on other sites More sharing options...
JohnA Posted July 31, 2006 Share Posted July 31, 2006 http://www.max-boost.co.uk/max-boost/intake/DV.htm The above link (if I have done it right) makes interesting reading, as does the whole site. good site that:innocent: Link to comment Share on other sites More sharing options...
michael Posted July 31, 2006 Share Posted July 31, 2006 good site that:innocent: I heard that the chap responsible for it smells of wee Link to comment Share on other sites More sharing options...
JohnA Posted July 31, 2006 Share Posted July 31, 2006 ...stinks actually... I was just being nice, he's a creep (if you really want to know): steer clear Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 31, 2006 Share Posted July 31, 2006 Skyline RB26 plus vent to atmo BOV personal observations below: The following is based on my Skyline experience, with air usage measured by air flow meters before the turbos. It is not applicable to cars that solely use a MAP sensor and throttle angle for air measurement . To recap I put in a bigger intercooler and the standard Skyline duct that runs across the lower front of the car taking dumped air from the 2 blow off valves to the intake between the air flow meters and the twin turbo inlets was masking air exiting the lower 4 rows of the new IC. Having spent a good deal of money on this item it pained me to see some of effectively blanked off. So I decided to blank the inlet off altogether where the cross pipe entered the turbo inlet ducting, remove the cross pipe and vent to atmosphere. The dump valves were being held open at idle by the idle vacuum level, so after ages of pondering i made a set up of solenoids to control when vacuum was applied to the dump valves. This set up worked perfectly. *HOWEVER* a much more serious problem occurred, which any similarly inducted turbo car will potentially suffer if the boost air is dumped to atmosphere rather than as standard into the air intakes after the AFM (s). On the overrun, after a period of boost running, the standard set up will recirculate the excess boost back into the turbos, through the IC, and back through the dump valves to the turbo inlet again until the turbos inertia has slowed them to the point of little or no boost. The AFM's do not see any more air entering the engine, as it is being recirculated. However, when we dump to atmosphere, that air is lost from the system and the turbos draw in fresh air via the AFM (s). This causes the engine to go mad rich, as the throttles are closed and no fuel is really needed. Hence the black smoke seen on the overrun after my mods. Worse still was a noticeable but very short period of detonation when coming hard back on the throttle. This puzzled me totally, then it dawned. As the fuel system started working normally again the Lambda sensor "caught up" with what was happening, saw a very overly rich mixture, and shut down the injector pulse width, creating a very lean mixture, causing a brief, but very dangerous period of detonation! I spent the afternoon and evening making new bracketry for the IC, new hoses and adaptors and shifting the IC forward that critical 40 mm or so, enabling me to fit the original moulded duct from the BOV's behind the IC without blocking it. Quite a lot of work and fabrication... However, the mod I was planning could well have caused damage, and is certainly something to be very aware of if one has a similar AFM pre turbo set up changed to dump boost to atmosphere. The type of BOV matters not, it's the fact that the air no longer re circulates but is lost from the system, confusing the AFM (s) into thinking the engine is wanting more air/fuel mixture. An oscilloscope on the O2 sensors confirmed what was happening. We live and learn, often the hard way, but in this case not as hard a lesson as it might have been. I hope this helps, I searched the web long and hard for references to BOV problems, and failed to find any details of why dumping to atmosphere on none MAP sensor systems, that aren't mapped for this, is potentially dangerous. Link to comment Share on other sites More sharing options...
Ruff_Rider Posted July 31, 2006 Share Posted July 31, 2006 How many turbocharged cars in the world have BOV's? How many turbocharged cars in the world have had trouble due to a BOV being fitted? Link to comment Share on other sites More sharing options...
Guest Mikethevice Posted July 31, 2006 Share Posted July 31, 2006 i currently have a 200sx S14, bailey dump valve fitted and it does over fuel upon lifting off the throttle means a loud pop and occasionally followed by a foot long flame thats all! Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 31, 2006 Share Posted July 31, 2006 No turbo engine I have ever built has had one, I never use them at all. Link to comment Share on other sites More sharing options...
michael Posted July 31, 2006 Share Posted July 31, 2006 How many turbocharged cars in the world have BOV's? 45 How many turbocharged cars in the world have had trouble due to a BOV being fitted? 34 I don't think anyone is saying the generic 'BOV' is the issue here, it's the type of BOV that causes the problems on certain cars (UK Supras, certain MR2s etc), usually when a standard recirc is replaced by a vent to atmos type. Link to comment Share on other sites More sharing options...
squiffy Posted July 31, 2006 Share Posted July 31, 2006 http://www.max-boost.co.uk/max-boost/intake/DV.htm The above link (if I have done it right) makes interesting reading, as does the whole site. argh! the c20let, bad expensive memories! Link to comment Share on other sites More sharing options...
Ruff_Rider Posted July 31, 2006 Share Posted July 31, 2006 45 34 I don't think anyone is saying the generic 'BOV' is the issue here, it's the type of BOV that causes the problems on certain cars (UK Supras, certain MR2s etc), usually when a standard recirc is replaced by a vent to atmos type. Are your sources accurate? I think not. Link to comment Share on other sites More sharing options...
TLicense Posted July 31, 2006 Share Posted July 31, 2006 No turbo engine I have ever built has had one, I never use them at all. Not even a recirculating one? Why not? In my book they're a longevity increasing component. I suppose the engines you're building are generally going to be rebuilt every few races, or maybe at best a season, so you wouldn't really have to worry about it? I wouldn't have thought many race engines would have an AFM? We all know how much of a restriction they are, and the lost air doesn't bother a MAP based system. Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 31, 2006 Share Posted July 31, 2006 IMO and that of some of the UK's top turbo experts, the BOV was "created" by Bosch for the 944 Turbo and the Cossie Sierra solely to reduce noise from the compressor on gearchanges. None of them have seen ANY evidence to suggest they decrease spool time or aid longevity. Neither have I, it's one more thing to go wrong, added plumbing and weight, and something else to package. I have never had issues even on fairly wildly boosted road car engines doing pretty high annual mileages (Volvo 240 2.1 litre B21A engine, running 1.6 bar and 330 BHP, doing 15,000 a year over 2.5 years, on plain bearing Holset turbo, which is old tech, with no water cooling to cassette, and a pretty cavalier attitude to cool down, warm up, and general well being of the engine. Experts are the top guys at Turbo Technics and Turbo Dynamics, and Ken Brittain of Brodie Brittain Racing, all of whom have pretty impeccable long standing credentials in this arena. And me of course, but I am just an over opinionated geezer from the sticks Link to comment Share on other sites More sharing options...
SteveR Posted July 31, 2006 Share Posted July 31, 2006 Very interesting reading Chris Link to comment Share on other sites More sharing options...
TLicense Posted August 1, 2006 Share Posted August 1, 2006 And me of course, but I am just an over opinionated geezer from the sticks If that's the case Chris, why would you suppose Toyota fitted one as stock? Same thing to reduce compressor noise? Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 1, 2006 Share Posted August 1, 2006 For sure, yes, most originak owners wouldn't like the squeak on lift off at high boost. IMO. Link to comment Share on other sites More sharing options...
Daston Posted August 1, 2006 Share Posted August 1, 2006 dont car's like the new Lotus Exise (how ever you spell it) and Noble have very loud waste gate/bov noise Link to comment Share on other sites More sharing options...
Bobbeh Posted August 1, 2006 Share Posted August 1, 2006 I don't think anyone is saying the generic 'BOV' is the issue here, it's the type of BOV that causes the problems on certain cars (UK Supras, certain MR2s etc), usually when a standard recirc is replaced by a vent to atmos type. The ONLY problem I've heard about BOVs on UK Supras are on the autos and regard lumpy idle and stalling , I've used the HKS SSV for the past 3 years without issue. Link to comment Share on other sites More sharing options...
Simon Posted August 1, 2006 Share Posted August 1, 2006 Interesting, so removing the bov wouldn't have a detrimental affect on the system? Link to comment Share on other sites More sharing options...
JohnA Posted August 2, 2006 Share Posted August 2, 2006 ..the BOV was "created" by Bosch for the 944 Turbo and the Cossie Sierra solely to reduce noise from the compressor on gearchanges. That is my recollection as well. It was meant to make the engines more 'civilised', not faster None of them have seen ANY evidence to suggest they decrease spool time or aid longevity... I have seen some anectotal evidence of this on bikes. Up to 1 bar it made no difference, but over 1 bar it made a difference in spoolup when shutting the throttle and opening it wide again. I don't think it was placebo. Link to comment Share on other sites More sharing options...
TLicense Posted August 2, 2006 Share Posted August 2, 2006 For sure, yes, most originak owners wouldn't like the squeak on lift off at high boost. IMO. What do you think would have been causing the squeak? My thinking is that effectively your reducing thrust loading by using a BOV of some kind. It may be have the effect of nine tenths of feck all, but the physics doesn't lie. There will be a direct reduction in axial loading on the compressor by fitting a system to relieve pressure once the TB is closed. There's an indirect effect in that your not accelerating and decelerating the turbine as drastically, which will have an effect of life. Again probably a gnat's cock in the grand scale of things, but I guesss that's where the level at which modern engine design is. IMHO. Link to comment Share on other sites More sharing options...
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