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Thread: Bypass valve small points (+ a boom theory!)

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    Default Bypass valve small points (+ a boom theory!)

    I've noticed something that is quite counter-intuitive that has been discussed before (smoother power delivery reverting to stock bypass valve), but now I want to drill down into it a bit more.

    Modest modset : intercooler,turbo inlet, turbo manifold, race pipe, HKS bypass, hypertech tune.

    I had a HKS bypass valve. I read about smoothness, wondered if the HKS being a bit more complex (two stage) might be an exception to that observation, then a week ago had the OEM bypass re-installed.

    It was very smooth before so I wasn't expecting much.

    Improvements with OEM replacing HKS include:
    Shifting to third gear.
    Shifting in general.
    consistently improved torque response.
    Less/No exhaust crackle/pop (usually miminal previously)

    Contrary to the "smooth" observation others had when reverting to OEM, I had smooth build-to-full-spool before, and now it's coming on hard and early. Nothing wrong with the driveability there's just a big jump at the very bottom end in available torque, and it's a noticable shove - (more and sooner) sudden onset boost.

    In a nutshell, I figure the OEM bypass is bypassing a lower volume than the HKS.

    This explains disappearance of pop/crackle on shift-overrun : While the system is in bypass, the MAF sensor does not produce linear readings. For the period in which the bypass is venting, the MAF will return a value that is less than the actual intake into the combustion chambers.

    Unknown exactly how the ECU compensates for this, but it will be either a constant correction value applied when appropriate, or it's a value calculated from observing other sensor feedback.

    For the purpose of explaining the pop/crackle with HKS vs none on OEM, let's presume that the ECU uses the simplest componsation method : The OEM bypass valve's recirculation characteristics are used, defined as constants.

    So during bypass the ECU essentially takes an educated stab at the volume of air entering combustion chambers, based upon sensors - but (possibly) assuming the bypass bleed rates of an OEM valve.

    The HKS bypassing a greater volume of air then, leaves less air entering the combustion chambers. But the ECU assumes it's educated stab is correct, resulting in rich fueling conditions. This, in turn, is evidenced by the slight crackle/pop on overrun that doesn't seem to be present with the OEM valve.

    So my questions are : How to best ensure that an aftermarket valve emulates the OEM one to best effect? To what extent is this something that can be adjusted? Was my HKS set too "soft"?

    And the boom theory is this: If the ECU is encountering the above scenario, and running rich during bypass, then it's certainly running lean at some point soon afterwards while the system is equalizing. If that effect is pronounced enough.....then potential boomski!

    ---------- Post added at 07:20 PM ---------- Previous post was at 07:05 PM ----------

    The sudden onset of bottom end boost, I suspect is due to the ECU 'picking' the OEM bypass, so to speak. I'm thinking there's a feedback loop between boost and wastegate, and that the OEM bypass bleed rate is an influence on this. So the observed behaviour fits if the ECU holds a constant -that reflects the bypass characteristics- used in calculating and compensating.

    THEORY : Replace bypass valves means adjusting this ECU constant - if it exists.
    Last edited by Nexus; 29-08-2011 at 07:23 PM.
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Michelin PS5 - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - Corksport turbo manifold - HT 98 octane tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - Bespoke Raspberry Pi Android based GPS/Carplay and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

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    The simplest question is - will tightening the HKS up get me OEM bypass characteristics. Time to ask some appropriate mechanics, I think....in the meantime...happy to be told I've just had the HKS set too soft...I thought it was fine...
    Last edited by Nexus; 29-08-2011 at 09:49 PM.

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    Is it difficult to adjust? If not, just try it. You have more than enough logging gear to see what happens

    Interesting post.

  4. #4

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    i have a turbosmart 50/50 BOV and from the stock bypass valve i noticed alot.

    For example: i sniff the accell in 1st, 2nd or 3rd and i get wheel spin very easy, with the standard bypass i have to give it a boot full for the same effect.

    I have a 3" Turbo back system on mine, i did notice a increase of crackle and pop, but i like that in moderation.

    the oem bypass i did notice a little hole in the plastic, this is what i believe does the smoother delivery, but does not hold boost very well.
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    I think most or all the above is complete tripe and probably over-analysis of a non-issue.

    1st, A BOV, or BPV or whatever you have or wish to call it, as long as it is not "leaking" (i.e faulty), will not influence "power" or "smoothness" for it is not intended to open unless the throttle is closed, when you won't be developing any power anyway. Power on, the pressures above and below the piston are equal, so the piston won't be going anywhere.

    2nd, If you are running stock boost then the OEM BOV will not leak when throttle on (unless it is faulty) and it is debatable if it does with higher levels of boost (up to the max recommended of nominally 18psi) anyway.

    3rd, As to the "crackle and pop" aspects, a BOV should be set so as to (largely) eliminate backfires which are a sign of an excessively rich unburnt mixture and hence washing your cylinder wall lubricant with raw fuel, and unnecessary sooting up of your cat(s).

    4th, A BOV should be tuned heavy enough to eliminate backfires but not so heavy that the turbo stalls because the BOV is not opening sufficiently to do its intended job.

    5th, There is just sooooooo much crap written about BOVs but they are pretty simple devices with a pretty simple set of intended and possible functions, yet folks treat them like they are the be all and end all of tuning. I guess it is because they have a little twiddly thing on top that unwise folks can easily get their hands on and play with and get a noise out of which they invariably confuse with enhanced performance. "If it's noisy it must be going better" is a non-sequitur
    Last edited by Doug_MPS6; 30-08-2011 at 03:34 PM.
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    I think you've missed the point of 90% of what was written. re-read it please. It's written with a knowledge of high-order control systems, which is what the ECU is.

    >3rd, As to the "crackle and pop" aspects, a BOV should be set so as to (largely) eliminate backfires which are a sign of an excessively rich unburnt mixture and hence washing your cylinder wall lubricant with raw fuel, and unnecessary sooting up of your cat(s).

    OK, you're pretty close to the point there. Read the first post, then consider the control system and this point together.

    I'm not complaining, I'm looking for constructive feedback "I feel is tripe" is not good feedback, nor is it objective. "I know it's tripe because..." is. You downplay the influence on the tune, but the whole point is that they MUST be an influence on the tune, and different characteristics will influence it in different ways.

    Your over-simplification of the influence of bypass valves is OBVIOUSLY an oversimplification, as there are MULTIPLE OBSERVERS reporting changes in behaviour when aftermarket bypass is replaced with OEM. If your overly simple interpretation was correct, NOBODY would be reporting anything, because there'd be nothing to report.

    Lastly, one specific observation proves you wrong : This simple device can't possibly affect low-end spool just by replacing it. UNLESS it has an influence on the tune. I can't think of anything a bypass valve can do to improve bottom-end spool and boost EXCEPT by an influence on the tune.

    Appreciate the input, however, what I am looking for is greater understanding - MORE detail, not dismissing the small points because they are small points, which is what I feel you are suggesting. You seem to understand that I am wanting to discuss small points - you obviously know they are small points. That's what I want to get an understanding of - if possible. Not to ignore them - pay attention to them.

    We are looking to explain observed behaviour from multiple owners. I am NOT certain, but I AM confident in the thrust of the analysis.

    As I explained at the outset, the observations are counter-intuitive. Nobody's talking about noisier=better. What we are talking about is how our bypass influences the tune. Not saying it's the be all and end all of tuning, either. Just saying that there certainly seems to be an influence, and asking for input in helping to understand exactly what is happenning.

    Not interested in ignoring the small points. Interested in focusing on them.

    Quote Originally Posted by Doug_MPS6 View Post
    I think most or all the above is complete tripe and probably over-analysis of a non-issue.

    1st, A BOV, or BPV or whatever you have or wish to call it, as long as it is not "leaking" (i.e faulty), will not influence "power" or "smoothness" for it is not intended to open unless the throttle is closed, when you won't be developing any power anyway. Power on, the pressures above and below the piston are equal, so the piston won't be going anywhere.

    2nd, If you are running stock boost then the OEM BOV will not leak when throttle on (unless it is faulty) and it is debatable if it does with higher levels of boost (up to the max recommended of nominally 18psi) anyway.

    3rd, As to the "crackle and pop" aspects, a BOV should be set so as to (largely) eliminate backfires which are a sign of an excessively rich unburnt mixture and hence washing your cylinder wall lubricant with raw fuel, and unnecessary sooting up of your cat(s).

    4th, A BOV should be tuned heavy enough to eliminate backfires but not so heavy that the turbo stalls because the BOV is not opening sufficiently to do its intended job.

    5th, There is just sooooooo much crap written about BOVs but they are pretty simple devices with a pretty simple set of intended and possible functions, yet folks treat them like they are the be all and end all of tuning. I guess it is because they have a little twiddly thing on top that unwise folks can easily get their hands on and play with and get a noise out of which they invariably confuse with enhanced performance. "If it's noisy it must be going better" is a non-sequitur


    ---------- Post added at 07:07 PM ---------- Previous post was at 07:04 PM ----------

    There is no requirement to adjust the HKS mazdaspeed blow-off valve kit according to HKS. You can adjust it slightly, but it should not be necessary. As far as HKS is concerned the valve ships with the appropriate adjustment.
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Michelin PS5 - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - Corksport turbo manifold - HT 98 octane tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - Bespoke Raspberry Pi Android based GPS/Carplay and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

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    Have you seen this topic on MSF? Goes into a fair bit of the detail you might be chasing:

    Discussion on how bypass valves can affect LTFTs. - Mazdaspeed Forums

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    NEXUS, Hi. I appreciate your comments. I didn't set out to suggest that there is no improvement from OEM to aftermarket. There is. I only suggested that it is unusual for OEM valves to "leak" as often as they are reputed to, seemingly as some sort of justification for buying a new aftermarket BOV. The reason for going aftermarket is tuneability and capacity, so that you can increase and/or direct the amount of bypass air enough to prevent turbo stall but not so much as to constrain, restrict or limit a fast turbo spool up when back on the throttle.

    BOVs ARE simple devices and have but one simple function, to provide a mechanism for intake air under boost pressure to have somewhere to go so it doesn't stall the turbo when the throttle plate closes and cause a back-pressure wave. The relationship with the MAF is there but only as an incidental one, in the sense that the MAF does not determine BOV function, nor the converse, although the BOV deals with the issue of backfires induced by mixture imbalance brought on by the MAF initiating a fuel loading via the ECU for air that is no longer fed to the cylinders. The only alternative is to dial in a fuel cut. Most folks don't bother if they aren't running 100% VTA.

    In this context is is notable that diesels do NOT have BOVs as they do not have a throttle plate.

    Incidentally, the fact that BOV-dom holds some weird magic for some people is shown by the remarkable number of diesel-driving lunatics out there who want their turbo-diesel SUV sod-buster to "have a BOV sound". One's mind can only boggle!

    Cheers.
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    Quote Originally Posted by Doug_MPS6 View Post
    Incidentally, the fact that BOV-dom holds some weird magic for some people is shown by the remarkable number of diesel-driving lunatics out there who want their turbo-diesel SUV sod-buster to "have a BOV sound". One's mind can only boggle!
    "But, But, But... The kenworth beside me has BOV noises, and it's a turbo deisel!!! WAAAH"

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    Quote Originally Posted by Victa View Post
    "But, But, But... The kenworth beside me has BOV noises, and it's a turbo deisel!!! WAAAH"

    Air brakes FTW...

    Chris.
    I work for a company that rents out Diesel Generators. You should hear a 50ltr 16cyld Twin-turbo Marine Diesel motor putting out about 1200kW

    Usually there only running at 1500rpm but they can make some noise!


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    Quote Originally Posted by Victa View Post
    "But, But, But... The kenworth beside me has BOV noises, and it's a turbo deisel!!! WAAAH"

    Air brakes FTW...

    Chris.
    Oooooh, is that what the noise is....
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    Quote Originally Posted by slixx View Post
    I work for a company that rents out Diesel Generators. You should hear a 50ltr 16cyld Twin-turbo Marine Diesel motor putting out about 1200kW

    Usually there only running at 1500rpm but they can make some noise!


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    I wonder if any of them were Mitch-built (MPS2NV). That'd be too funny


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    Thanks. Don't mean to be testy. Specially the ltft thread.

    I continue to be a little amazed. 6th gear has come alive - it's happily thumping away at lower rpm. spool has definately dropped ~300rpm? It's really noticable. I might peg spool @ 2200rpm now instead of 25.

    Here's what I'm expecting to see - I probably have some logs from past that I can compare against. Lambda showed a distinctive pattern of behaviour on lift off. It got quite lean a short while after and then wobbled it's way back to equilibrium. I'm very strong on theory but don't have the hands on experience to be confident I'm interpreting appropriately. What I am expecting to see is the lamda stay within tighter boundaries, prob still stray around a bit on bypass, due to the MAF uncertainty, but I expect I'll see it holding tighter.

    That MAF uncertainty during bypass is the crux of the tuning influence. The control system takes corrective actions etc based on sensor input, but the discrepency between it's hard-coded expectation of bypass conditions, and the actuality of bypass conditions gives rise to all the known symptoms - rich @ bypass (crackle-pop), etc. This effect is also going to be more pronounced the greater the volume of air you have to bypass. Very long plumbing solutions with very big frount mount intercoolers could give rise to the (still theorised) lean-after bypass condition becoming exaggerated to the point of boom. This would perfectly explain some of the legendary mystery boom behaviours - "wasn't on it had just been and then done a fairly gentle squirt...." bypass, lambda all over the shop, back on it - even just a bit - before the system has equalised again, and for no apparent reason....massive knock + boom. Because ECU thinks there's a lot less air in the system than their really is. It has over estimated the volume passing through the engine in bypass conditions.

    Just putting it there as a theoretical possibility, please don't shoot it down without imparting some knowledge of why.

    I expect that it might be something custom tunes handle better but with the hypertech definately I would say : Don't install a bypass.

    re: 50/50 turbosmart (?) This ccould potentially mitigate the ECU's miscalculations - potentially - bleeding to atmo removes some air from the system. since the ecu is theorised to be overestimating air consumed during bypass, bleeding some of the excess air from the system (to atmo) might improve the ecu's recovery times. These were about 2 seconds or more if my lambda observations and interpretations are correct. This is where it can get very interesting - and very complicated. It is certainly VERY possible for a high order control system to become unstable in such circumstances, which might be evidenced by lambda jumping around and entering dysfunctional conditions before recovery.

    ---------- Post added 05-09-2011 at 12:05 AM ---------- Previous post was 04-09-2011 at 11:44 PM ----------

    Adjusting the HKS is possible. There's a fine- adjustment of tension - then further adjustment of the same results in shorter throw of the valve. HKS calls this "over adjusted". However it occurs to me that restricting the throw will ultimately affect the volume of air at the second stage bypass, disabling it and restricting the valve to a single stage if you persisted, I expect. Never the less, might be all that is needed to emulate the OEM valve characteristics better.

    ---------- Post added at 12:40 AM ---------- Previous post was at 12:05 AM ----------

    Quote Originally Posted by TD View Post
    Have you seen this topic on MSF? Goes into a fair bit of the detail you might be chasing:

    Discussion on how bypass valves can affect LTFTs. - Mazdaspeed Forums
    Very good. I can only see one mistake. Almost the same interpretations, back to front on one aspect :

    >> My hypothesis is that our ECU is programmed to expect a low release point, since the stock BPV has a relatively weak spring holding the valve shut. I think that this stock Release Point is expected to be DURING the operation/learning range of the heavy throttle LTFTs. This is the same LTFT that is used during WOT (Open Loop) operation. When you add an aftermarket BPV which raises the Release Point of the BPV such that it puts it out of the operation/learning range of the heavy throttle LTFTs, which means that the ECU will learn these LTFTs with a fully shut valve (vs the slightly leaking recirc of the stock weak spring), which means that more air would actually get into the engine, making the ECU calculate higher LTFTs, since it sees more air in the system than it's used to (making it add more fuel). This illustration shows what I mean by increasing release points putting themselves out of heavy throttle LTFT operation/learning range:
    His theory is that the ECU "sees more air in the system than it's used to (making it add more fuel)". But the ECU can't possibly see that once the bypass is open as the MAF sensor is the point at which the air enters the closed system. The bypass is within the system, once the air is in the system, either all the air is going in (closed bypass under boost) or it's not (bypass open) - it might add fuel if the valve opened later, as not being in bypass, there's a touch more air entering the system.

    It's the bypass open conditions that we are both theorizing are hard-coded. My point is the ECU can't use the MAF to gauge volume in the combustion chambers during bypass, specifically because the MAF will be reporting no air entering the closed system while the air already there recirculates until it's consumed, the MAF becomes near real-time again, and the ECU ceases to rely on hard coded expectations of bypass conditions.

    His theory is ECU calculating bypass conditions before the system actually does etc...assuming valves open later hence more air through maf...
    Mine is that the ECU is calculating bypass conditions differently to how they actually are....but I am actually suspecting the aftermarket valve to be "softer" and quicker to release and releasing more.

    I haven't read the whole thread - I would disagree about the OEM valve leaking - it doesn't - and I also wonder about the valve being software than after markets. I don't think these things are necessarily true - certainly 2XS had no trouble with 25 psi and OEM bypass if I recall....

    Without a custom tune, I think it is best to emulate the OEM characteristics as much as possible, so next step is to watch that lambda and see what it's doing with the oem valve etc, then inspect the HKS setup and see what might emulate OEM best.
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Michelin PS5 - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - Corksport turbo manifold - HT 98 octane tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - Bespoke Raspberry Pi Android based GPS/Carplay and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

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  14. #14

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    Interesting thoughts NEXUS and it's good to see someone thinking hard about the technicalities in detail.

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    First chance to run a log today. From the glances I stole at the display, lamda does hold tighter, but that's a far from scientific observation for now. It seems wanders less and achieves equilibrium quicker than I recall last time. I've disabled the bluetooth I used to use for logging and now running with USB - so much better, so much less latency. But I don't think I'm seeing something I just expect to be there, or an artifact of faster logging - and when I find a comparable historical log, I think it'll show the variation.

    Having said that, I now realize the lean condition that made me take notice of it in the first place, and start watching what it was doing, is the injector shutdown that occurs in some circumstances. Nevertheless, I felt lamda recovered quicker in this circumstance too.

    So I would be wanting to log runs with HKS, OEM and another at some time in the future, taking care to be logging gentler lift-off (back-off) but not overrun, because I think this is where the differences will be measurable utilising OEM sensors.

    The next approach would be to place a MAF housing in the recirc path and actually measure it - hypertech, if I recall, claim to have done exactly that during development, and also stated that the stocker holds boost and they couldn't find a reason to recommend upgrading it. This leads me to feel that the MAF characteristics that hypertech measured with a recirc MAF feeds into how they've tuned it. Agressively expecting those measured recirc flow characteristics...

    The previous LTFT thread from mazdaspeed forums definately on a similar track.

    Also suspect that the negative influence of inaccurate recirculation modelling at the ECU may influence the system in a similar way to badly heatsoaed TMIC with high IAT....

    Accelleration from 80-110 in 4th gear logged 175Kw 320Nm. 110 in 4th gear is what - 4500rpm? Does that Nm figure stand scrutiny against the Kw? I suspect it's displaying ft-lb and displaying that as Nm, making correct figure 430Nm if so) - bug in the dashboard rather than logging. I think. Or I'm unclear on flywheel vs wheels for the torque figure. Kw I am certain is ATW. Will have to chack manuals ...
    Last edited by Nexus; 18-09-2011 at 07:56 PM.
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Michelin PS5 - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - Corksport turbo manifold - HT 98 octane tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - Bespoke Raspberry Pi Android based GPS/Carplay and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

    "Lipstick" 2013 Velocity Red MPS 3 - 18x7.5+48 Enkei RPF1 -225/40R18 Federal RS-RR - CPE TMIC - COBB inlet - CPE stg 2 mount - COBB Stage 1 98 octane tune - COBB shifty knob - 2XS short shift - 2XS turbo manifold.

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    175Kw 320Nm ATW it is. Factoring in 15% drivetrain loss, that's 376Nm @ 4500rpm. No dash bug. 430 - wishful thinking.
    Nice to see 175Kw logged for a real-world squirt! Presuming the peak is higher in the rpm range, happy me.

    But I was suppsed to be comparing logs of lambda.....

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