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P.S- Pop off valve = no bueno

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Old 01-28-2008, 02:27 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
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Originally Posted by 930gt-40r View Post
hey, speaking of wastegates, does anyone in here have experience with the Tial 44 v-band gate with a large frame turbo? I am going to run a divided T-4 housing on my 37 for quicker spool-up and wanted to know if I should maybe purchase a second 44 wastegate to regulate it. I know that the V-band housing is much newer and more efficiant than our old 46 gates.

P.s Is anyone interested in a Tial 46 gate, I got one for sale.
no data but I have been selling a bunch of 44's lately so maybe that answers your question and primarly p-car guys
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Old 01-28-2008, 02:40 PM
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Alright this is good, we're back on track with a good Pelican thread here I'll first go an apologize for jumping down Gorans' throat. I was tired this morning and one thing that bugs me bad is discrediting someones work w/o first asking questions about it to better understand the general idea and knowledge behind it. No hard feelings I hope?

Ok I'm going to try to explain the issue here with these Evo's and my reasoning for doing what I've done the best way I can here in a post. I have alot of information jumbled in my head right now and this may not be that easy for me to translate it all into text without it getting confusing or off track so please please please bear with me here. This may be quite long and may jump into multiple posts pending if there's a character limit. This is most definitely OT and not Porsche related but here it goes:

The Mitsubishi Evolution is the car in question, both the older Evo 8 models and the newer Evo 9 GSR/MR models with the MIVEC 4g63 engine. The car is equipped with a 2.0L 4 cylinder forged internal engine. Boost is provided by a big 16g mitsu compressor mated to a 9.8(8) or 10.9(9 GSR or MR) twin scroll turbine and manifold setup. These cars are well know for making crazy power at rediculous boost pressures(1.8-2.6bar) and doing so with the ability to open source tune any part/map in the OEM PCM. As such, you end up with a "import tuner" type of car with kids throwing a mass of aftermarket parts at the chassis to tap the cars potential.

The issue that affects 95% of all the Evo 8 + 9 cars revolves around the diverter valve and track use or any sort of low load/throttle modulation. The DV setup on these cars is not unlike any other car, however the car suffers from what appears to be an EXTREME level of DV sensitivity to throttle input against engine RPM and load. If there is a slight load on the engine while driving and you attempt to modulate the throttle in any attempt to control the car(say like throttle steering through a corner) the DV dumps under throttle, causing a massive unsettling of the car. In some instances, this can also be noted on long gradual uphill jolts, when a very light but continuous hold of throttle will eventually lead to a DV dump at mid to upper rpms.
This one Evo here in particular has had numerous close calls at Watkins Glen while running through the esses. Car bucks and dumps mid corner causing unsettling no different that if you lifted off the gas completely or hit the brakes mid corner. This is very scary stuff as it's totally unpredictable. Most of the Evo's I've tuned and dealt with run anywhere from ~315-430AWHP, so an unsettling in a car with that kind of power usually comes at elevated speeds as well. Stuff that I know 99% of the members here are well aware of or have experienced themselves out on the track.

At first the cause was thought to have been issues with the DV itself. Then the 272 degree camshafts were thought to be the root cause, as well as the various intakes, charge piping, FMICs, etc etc. This however was soon squashed when Evo owners with nothing more than a little boost and a reflash caught wind of my research and started advising me that their cars suffered the same issue. More and more people started popping up, every car different and all had the problem. After a few months of probable causes, prototype isolators and parts, and countless tests on damn near every modified Evolution in the area nothing stood out as a root cause. All the car were different in their own right, but all had this bucking/dumping issue. Some thought that intake disruptions were causing a backfeed to the MAF, upsetting the PCM fuel/timing signals but again squashed when a few MAP based Evo's showed this signs. The last ditch effort and possible cause came about from talks with some aviation engineers who dealt with high altitude aircraft turbo charging. The one part that damn near all the afflicted car had in common was the stock turbocharger, with say but a few that had custom kits with spools like 18G's or 28R series Garretts.

The stock turbocharger spools incredibly fast. We regularly run boost pressure in excess of 25+psi all day long on stock blocks and don't break a sweat. The twin scroll turbine and low mass 16G compressor lead to some seriously fast spool rates. This one car here will see 25psi around 2900rpm from 2nd gear on out if it means anything. Now over the course of the trails with this problem we had discussed the compressor map in general and all the math you could compute kept putting us well in the efficiency range of the compressor but we never took into account the WAY the compressor got there nor how it was affected during low/partial throttle modulation.

Knowing a bit about turbochargers myself what I ended up doing was making a special intake tube to house an optical RPM reader from my VSR balancing machine so I could observe and monitor the CHRA speeds of a 16g while operating the engine at load. I also plumbed in pre/post IC boost gauges and pre IC charge temp gauge to log and diagnose exactly what the turbocharger was doing at these boost levels. Over the course of a couple weeks, I logged the information and discused it again with various people in this field and we determined(guessed more like it) that throttle modulation was causing the compressor to surge at mid level pressure ratios, right around where these turbos run in their sweet spot. Because the turbocharger spooled up so fast in reference to engine RPM and flow requirements the compressor would function fine at mid-to-WO throttle levels, but any sort of low level throttle modulation with a light engine load would hypothetically cause the compressor to shift into surge as the CHRA would still spool up rather quick at those throttle input levels, even though the airflow requirement of the engine was low at that point. It is thought that this compressor surge was causing flow disruptions to the air going into the motor itself, which subsequently tripped the DV into dumping while ON the throttle. Sound weird? Tell me about it. This is the best way I can explain it right now. Alot of it hypothetical yes, but it's the best I've got so far.

*****CONTINUED BELOW*****
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Old 01-28-2008, 07:52 PM
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****CONTINUED FROM ABOVE*****

Anyway onto the valve "fix". After discussing this issue with the aviation guys the idea came up to attempt to vent off and control boost pressure through the DV valve. I won't get into the details of the valve itself, but it does have the ability to act as both a "wastegate" and a diverter valve/BOV simultaneously with some creative plumbing and simple electronics. It was never designed with this application in mind, it was just something we figured out along the way and managed to make it work. The patent for the valve is available online to read for more details.

As Goran stated(correctly I might add) one root effect of venting boost pressure like this is you essentially shift the operation point of the turbocharger in the compressor map towards the choke. In just about every application this is not beneficial however that was was we trying to do on this car. By "shifting" the map you could say, the operation area of the turbocharger shifted away from the surge line of the map in an hypothetical attempt to keep the compressor well within the efficient area of the map during this low-to-mid level throttle modulation under light engine load. Blah blah blah right? Anyway at this rate one could easily say the simple fix is to change out the turbocharger to a properly sized unit. This is true to some effect, however even the like of the 2871/76R's have this problem. Car equipped with 3071/76R and larger turbos seem to be immune from this(hypothetically due to the map changes), however these options completely kill low speed drivability and cost in excess of $3-4K for a kit, plus install. 90% of Evo owners don't want this option and need a simpler, cost effective solution that retains the stock turbocharger. Whatever the reason being, what I have done has effectively eliminated this problem and the car now runs fantastic.

Onto the other tidbits with tuning/dumped air/etc. At the begining of this valve idea I was well aware of the fact that the car would run rich due to the metered air being released pre-throttle with meter fuel being dumped into the engine. For once though e one must thank Mitsu for programming the stock computer as well as they did. The system is completely open source tunable, with the ability to rewrite the software in areas with different variables to suit ones application(up to a certain point that is). Needless to say, the correction and compensation for this 'air dump" has been fully tuned for and the fuel curve is as if the car was running your typical wastegate/bov setup. The car still does have the functioning turbocharger wastegate in conjunction with the "BOV wastegate" Both have their own separate boost controllers. Due to the readings from the optical RPM reader, post IC boost gauge, plenum boost gauge, pre IC charge temp gauge, and the divorced o2 housing with atmospherinc dump I know that the turbocharger is operating well within it efficiency range and that the wastegate is still operating as normal, regulating CHRA speed.

....side step here....the whole idea for operating the turbocharger at an increased boost level over what was required came from the aviation guys who have used this setup before in high altitude enviornments. Again as Goran said this would probably work on something that used an oversize turbocharger compared to engine volume. This idea was tried to see what it would yield on the car to this issue and showed no negative results aside from a 27 degree increase in charge temp over the 25psi boost level. If either way the 27 degree hike pre IC made no difference by the time it reached the stock IAT sensor after passing through the intercooler on this car. I have no intention on keeping this setup with this option, but wanted to pursue all avenues to eliminating this problem. Also as a note, in my previous post I think I posted that I had the turbocharger running at 29psi with the valve at 24. Mistype on my part as it's running 25/24psi.... turbo/valve.

Oh I'm getting lost in my own post here now I'm must say that I had no intention on raising a fuss with this little BOV thread here and never intended to insult people intellect on this subject. I'm just trying to say that whether it just be the circumstance and variables surrounding this car in particular, this setup is working, is tuned, and so far has not shown any detrimental signs. The turbocharger is still functioning in it's efficiency range and CHRA speeds. I had no intention to say that it would work in a p-car standpoint, or any other car for that matter, but to just rather point out the inginuity of the valve in general.

As another side note I think someone asked how I was able to make the valve function as both a "wastegate" and DV simultaneously and it really revolves around the internal makeup of the valve actuator and a simple system i whipped up composed of an adjustable vacuum/boost switch, check valves, and a solenoid to control where and when boost and vacuum reference signals actuate the valve. It simply dictates when the valve will see each signal, and what port(s) on the valve that will get those signals. By varying these signals to the port in different "combinations" the valve functions differently. Really sounds more complicated in text than it is in reality but wouldn't work with any other valve out there.

Ah I really don't know what else to post or say. I'm so lost in my own post here that I hope I didn't lose any of the people that were keeping tabs on this

I hope this helps clarify a few things here. I know that what Goran said was all true, I do this stuff too for a living. It's just that in this very specific application, the negatives of this setup seems to become positive and the ability to tune the car for it make it an avenue to pursue. Do I recommend you go do this on your car? Absolutely not. This is just an attempt to remedy an extremely common problem amongst the Evo community with a relatively cheap and 100% effective means of eliminating the problem for those that want to without resorting to expensive and daunting changes in turbochargers and the associated ancillaries that go with such a swap on these cars.

I'm pooped out

Please feel free to debate this. It's what we're here for. Debates are how I learn alot of my s**t as well so I like doing it. Also if there's something that needs better clarification please let me know and I'll jump in an do so ASAP.

-Best Regards,
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Old 01-28-2008, 07:52 PM
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Quote:
Originally Posted by 930gt-40r View Post
hey, speaking of wastegates, does anyone in here have experience with the Tial 44 v-band gate with a large frame turbo? I am going to run a divided T-4 housing on my 37 for quicker spool-up and wanted to know if I should maybe purchase a second 44 wastegate to regulate it. I know that the V-band housing is much newer and more efficiant than our old 46 gates.

P.s Is anyone interested in a Tial 46 gate, I got one for sale.
From my personal experience with setting up and tuning divided housings I find that it's best to regulate boost on both housing volutes, so you'd end up having a WG on either bank of the motor. It's not completely necessary if you're not using a true divided header setup(like if you bolted a divided housing to a standard flange header setup) but then at that rate you're not seeing the true benefit of a divide housing either. You'll have better control over boost levels and spikes with twin wastegates, and obviously better spool with a true divided manifold.

I've used the Tial 44mm valves with GT35's before and really didn't have a problem. Maybe a little bit of creep way up top on larger(3.5L+) engines but nothing really drastic. The new V-band flange wastegates do flow quite a bit better than the old four bolt housing did even though a little bit smaller in seat size.

I'd still use two wastegates though, just for the absolute best possible control over boost.

Hope that helps...
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Old 01-28-2008, 08:01 PM
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Quote:
Originally Posted by BoxxerSix View Post
-lots of text-
Adam,
I read the description but I need to check if I got it right.

Synopsis:
If I understood it right you have Mitsu EVO 8 with MIVEC 4g63 engine and Mitsu TD04 16g turbo with twin scroll input. Engine is stock apart from EFI being tunable. You increased boost to 24 psi and you have low load bucking problem associated with BOV dumping on throttle movements?

You mended the problem by running boost at 29 and dumping overboard 5 psi in-between by controllable pop-off?


Couple of questions:

1. Is ECU based on speed-density (=MAP sensor) or does it have metering device (hot wire?) I guess there is an AMM.

2. If metering device is present, how is it attached to turbo intake and what are lengths between filter-AMM-turbo?

3. Is OEM BOV of recirculating type? If yes, where is recirculation connected on plumbing in respect to filter-AMM-turbo? Is your new BOV also recirculating or open?

4. Is throttle operated by cable or is it TBW (electric)?

5. Do you have compressor map for your turbo? (I might have it if it's ordinary TD04 map)

And last, which puzzles me: Is you BOV venting air even at the low loads? I mean, if you tried to solve the problem with bleeding all boost above 24psi, you BOV would be kept shut under 24 psi and thus wouldn't bleed any air at low loads where you have the problem, no?

Regards,
Goran
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Old 01-29-2008, 03:25 AM
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Goran, I'll answer each separately for you

Quote:
Originally Posted by beepbeep View Post
Adam,
I read the description but I need to check if I got it right.

Synopsis:
If I understood it right you have Mitsu EVO 8 with MIVEC 4g63 engine and Mitsu TD04 16g turbo with twin scroll input. Engine is stock apart from EFI being tunable. You increased boost to 24 psi and you have low load bucking problem associated with BOV dumping on throttle movements?
This is correct for the most part. This particular car has a host of aftermarket parts, including aftermarket 272 degree camshafts. Other cars that suffer from this problem though range from nearly bone stock to fairly modified.

Quote:
Originally Posted by beepbeep View Post
You mended the problem by running boost at 29 and dumping overboard 5 psi in-between by controllable pop-off?
That was a mistype on my part in my previous post. Turbocharger boost is set at 25psi, controlled by it's own boost controller(off the compressor housing for boost only signal). Valve is set at 24psi, also with it's own boost controller(also off the compressor housing for a boost-only signal)

Quote:
Originally Posted by beepbeep View Post
Couple of questions:

1. Is ECU based on speed-density (=MAP sensor) or does it have metering device (hot wire?) I guess there is an AMM.

2. If metering device is present, how is it attached to turbo intake and what are lengths between filter-AMM-turbo?
Car is a hot wire MAS setup. OEM location of MAS is bolted directly off airbox, rubber corrugated tubing connects MAS to turbo inlet ~ 16" total length. This car is equipped with aftermarket style tube intake, other cars of different makes of intake as well as the stock ones. Filters. wheather OEM or aftermarket, are in very close proximity to the MAS if not bolted to it directly.

Quote:
Originally Posted by beepbeep View Post
3. Is OEM BOV of recirculating type? If yes, where is recirculation connected on plumbing in respect to filter-AMM-turbo? Is your new BOV also recirculating or open?

4. Is throttle operated by cable or is it TBW (electric)?
Car throttle is standard cable actuated(non TBW). Diverter valve is a recirculating type in OEM setup and is still recirculating with the new Synapse valve on the car. The recirculation dump on the intake tube has been moved and adjusted several times to see it's effect on MAS signal(no disruptions). The dump resides between the MAS and turbo inlet, OEM has it about 6" from the MAS

Quote:
Originally Posted by beepbeep View Post

5. Do you have compressor map for your turbo? (I might have it if it's ordinary TD04 map)
Yea it's not the standard Td04 map I believe. Compressor was changed a bit and it's specific to the Evo. I have it here somewhere, I'll look for the file. I don't have it labeled as "evo16" or something like of that nature like a smart person would OH!:

Quote:
Originally Posted by beepbeep View Post
And last, which puzzles me: Is you BOV venting air even at the low loads? I mean, if you tried to solve the problem with bleeding all boost above 24psi, you BOV would be kept shut under 24 psi and thus wouldn't bleed any air at low loads where you have the problem, no?

Regards,
Goran
On the stock BOV setup, the car operated as normal except this venting issue. The valve is shut anytime you are over 0hg plenum vacuum and doesn't vent at low engine loads/speeds UNLESS you start doing this throttle modulation. At low rpms(1500rpm and under) it's not that apparent as you're barely moving. However once you start to climb 2K rpms the situation get worse. The real big issue is when it's occurring at 4K+ rpms with some speed behind you. Any attempt to modulate the throttle at these engine speeds will surely have the valve open and dump back to the intake under load, releasing all boost pressure that the engine may be calling for.
The turbo on these cars is one mighty fast OEM spooling turbo. In most cases your capable of building 6-7psi of boost at a standstill by simply giving the motor a quick rev up to 5-6krpms. BTW, if it mattered OEM rpm limit is ~7200 but in most cases with valvetrain mods we swing these motors out in excess of 8500rpm all day long.

With the new valve it does exactly as you said there. It's closed all the time except when it needs to bleed off an extra 1-1.5psi of boost pressure at WOT and/or in between shifts to vent airflow and prevent compressor surge like any other valve does. I have easily compensated for this ~1psi of air bleed through the stock computer and AFR's are right on track throughout the RPM and load range of the motor. With this setup, I am able to completely modulate the throttle from 6hg to any boost level with zero dumping/bucking issue now(6hg vacuum mark is the limit to open valve for shift set by adjustable vacuum switch)


Also, the bleed air from the diverter valve is recirculated back into the intake post MAS/pre turbo as it is OEM.
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Old 01-29-2008, 04:43 AM
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BoxxerSix, I had the same surging feeling that your speaking of in my old Galant VR-4. I had the big 16G on it (10.5 hot housing) and if I did a partial throttle lift I would then get an abrupt bucking.

On another note, do you know The Shop? Jimmy K, Eddie B, and my self are building some pretty nasty 964 and 993s over there. Im just wondering as you live in the next state.
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Old 01-29-2008, 12:07 PM
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Adam, nice project review. You have a solution and hopefully happy customer(s). Good work.

There is a phenomena in the turbo world called compressor air noise. It's not discussed in the popular books on turbo applications. Some argue it's a soft SURGE, but surge none the less, as such the engine should be matched to the right of this region. Others call it aerodynamic instability and if it doesn't manifest itself in the actual application, as demonstrated by road testing, there is no harm. The problem is you have just introduced some very challenging NEW road conditions. It's often present in compressors designed for broad flow range needed of variable power turbine applications, just like yours. I suspect this compressor has it.
Old 01-29-2008, 12:15 PM
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Adam, I just Goggled compressor maps and found this information.
http://www.rbracing-rsr.com/turbosupermaps.html#t3

While it doesn't specifically show the TD04-16 the "family" of like compressors show the very distinct curvy surge line and mid range humped speed lines characteristic of compressors with air noise instability. They also show characteristic high efficiencies which are usually reduced somewhat to fix the problem.
Old 01-29-2008, 12:54 PM
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930gt-40R.......yes I actually do remember the old VR-4's and first gen DSM's having a similar issue. It seems Mitsu amplified the scenario on this chassis. I'm not familiar with The Shop. I'd love to stop by some time and sit and shoot the s**t with you guys. This time of year I'm sloooooooo as all hell anyway Shoot me an address or something in a message and I'll see if I can come on down anytime soon. I was just down at Dan's shop(Hairy Dog) last week doing a PPI on an '93 RSA for my buddy....

copbait73....thank you for the comments. It's been some time now since I initially started this daunting task. I did get your message and it's funny what you mentioned there as I was thinking myself if there was a way to machine an anti-surge style inlet to the compressor housing and see if it made any effect on the issue in it's own right.

Turbo is a TD05-16g(big wheel) on the car OEM, just not exactly sure yet if there's anything super special about it aside from the twin scroll turbine.

I think I am going to try and locate a lone compressor housing to give this a shot as well. I've machined compressor housings before to accept larger wheels, but have never attempted to machine in an anti-surge style inlet to a compressor housing that didn't have one from the start. Equpiment to do the work isn't the problem but rather I have no idea about the math involved in properly setting one up as such. Any thoughts...????

Hmmmmmmmmm..........
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Old 01-29-2008, 01:29 PM
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copbait73....this is a so so shot of the Evolution tdo5 B16G compressor housing






Not a huge amount of room for an anti surge/ported shroud on that housing but if I had a spare I'd be able to tell for certain. If it wasn't a 5 hours job to remove the turbo from this car I would just take this one off and measure that
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Old 01-29-2008, 01:51 PM
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Awwww... look how cute and little the 16G is.....
I remember that those were the first big deal on my old VR-4 unless you grew the b@lls and got an FP Green. Now when I see a 16G after working with a 37R it seems sooo tiny. Its funny how things evolve.

BoxxerSix- I know Hairy dog pretty well, Dan has got one hell of a shop-
Ill send you the address of The Shop, Im their on saterdays and some sundays working on the big projects that the master (Jimmy K) cannot tackle while conducting his business. That includes his race car...
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Last edited by 930gt-40r; 01-29-2008 at 04:58 PM.. Reason: because I kick @$$
Old 01-29-2008, 04:54 PM
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Quote:
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Awwww... look how cute and little the 16G is.....
I know isn't it, but man does it spool up right quick on these cars.

Love to come check the place out. My shop/bay is meager in comparison to most. All my good space resides in my 16K sq foot machine shop. I'm usually working on one car/project at a time because that's about all the room I've got for such things. I'm a one man show so it's a good thing I guess.

Yea shoot me that address and I'll plan on driving down to meet up with you guys in the near future. Maybe I'll bring the Evo down and let you bomb around in it for a little while, bring back the goo ol DSM days for a bit. Tranny and front diff are coming out in ~2 weeks for a much nicer gearset and R&P's so I'll try to work around that.
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Old 01-29-2008, 07:04 PM
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Goran, I'll answer each separately for you



This is correct for the most part. This particular car has a host of aftermarket parts, including aftermarket 272 degree camshafts. Other cars that suffer from this problem though range from nearly bone stock to fairly modified.



That was a mistype on my part in my previous post. Turbocharger boost is set at 25psi, controlled by it's own boost controller(off the compressor housing for boost only signal). Valve is set at 24psi, also with it's own boost controller(also off the compressor housing for a boost-only signal)



Car is a hot wire MAS setup. OEM location of MAS is bolted directly off airbox, rubber corrugated tubing connects MAS to turbo inlet ~ 16" total length. This car is equipped with aftermarket style tube intake, other cars of different makes of intake as well as the stock ones. Filters. wheather OEM or aftermarket, are in very close proximity to the MAS if not bolted to it directly.



Car throttle is standard cable actuated(non TBW). Diverter valve is a recirculating type in OEM setup and is still recirculating with the new Synapse valve on the car. The recirculation dump on the intake tube has been moved and adjusted several times to see it's effect on MAS signal(no disruptions). The dump resides between the MAS and turbo inlet, OEM has it about 6" from the MAS



Yea it's not the standard Td04 map I believe. Compressor was changed a bit and it's specific to the Evo. I have it here somewhere, I'll look for the file. I don't have it labeled as "evo16" or something like of that nature like a smart person would OH!:



On the stock BOV setup, the car operated as normal except this venting issue. The valve is shut anytime you are over 0hg plenum vacuum and doesn't vent at low engine loads/speeds UNLESS you start doing this throttle modulation. At low rpms(1500rpm and under) it's not that apparent as you're barely moving. However once you start to climb 2K rpms the situation get worse. The real big issue is when it's occurring at 4K+ rpms with some speed behind you. Any attempt to modulate the throttle at these engine speeds will surely have the valve open and dump back to the intake under load, releasing all boost pressure that the engine may be calling for.
The turbo on these cars is one mighty fast OEM spooling turbo. In most cases your capable of building 6-7psi of boost at a standstill by simply giving the motor a quick rev up to 5-6krpms. BTW, if it mattered OEM rpm limit is ~7200 but in most cases with valvetrain mods we swing these motors out in excess of 8500rpm all day long.

With the new valve it does exactly as you said there. It's closed all the time except when it needs to bleed off an extra 1-1.5psi of boost pressure at WOT and/or in between shifts to vent airflow and prevent compressor surge like any other valve does. I have easily compensated for this ~1psi of air bleed through the stock computer and AFR's are right on track throughout the RPM and load range of the motor. With this setup, I am able to completely modulate the throttle from 6hg to any boost level with zero dumping/bucking issue now(6hg vacuum mark is the limit to open valve for shift set by adjustable vacuum switch)


Also, the bleed air from the diverter valve is recirculated back into the intake post MAS/pre turbo as it is OEM.


Hmm...I believe you have oscillation/coupling problem made possible by 1. Quick spooling turbo 2. More boost 3. Valve that opens too easy. 4. Probably some MAP enrichment when mass flow starts to increase. 5. Weird compressor map


I suggest trying this:

1. Find a adjustable recirculating BOV, make sure it dumps air back between turbo and MAF, but as far away from MAF as possible. Don't us pop-of function.

2. Adjust it little harder, so it doesn't start opening and dumping until 4lbs

3. (If above doesn't help) fit a small strangling/delaying orifice between BOV articulation nipple and the hose to get rid of transient surging.
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Old 01-31-2008, 02:48 AM
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Originally Posted by beepbeep View Post
Hmm...I believe you have oscillation/coupling problem made possible by 1. Quick spooling turbo 2. More boost 3. Valve that opens too easy. 4. Probably some MAP enrichment when mass flow starts to increase. 5. Weird compressor map


I suggest trying this:

1. Find a adjustable recirculating BOV, make sure it dumps air back between turbo and MAF, but as far away from MAF as possible. Don't us pop-of function.

2. Adjust it little harder, so it doesn't start opening and dumping until 4lbs

3. (If above doesn't help) fit a small strangling/delaying orifice between BOV articulation nipple and the hose to get rid of transient surging.
Goran thanks for the input. All of this was actually tried months ago in many different formats with many different types of valve to no good effect. It only resulted in poor DV response and high amounts of compressor surge at throttle liftoff(shifting) as the valves reacted way to slow.

Issue turned out to be the compressor running over the surge limit when the engine wasn't calling for air. Just a bad case of a small, really fast spooling turbo at high PR's that just has a very narrow map.

I was going post last night but the bleed setup has solved the problem and the dyno runs yesterday proved no issue with it. Everything has been tuned properly and the car runs great. I didn't want to post this yet as I haven't digitized the dyno sheets to show the TQ/HP curves and their changes as well as the AFR plot and wanted to post those with the end result to sho the differences.. Plotted standard setup pull against my bleed setup. Had to sacrifice a tiny amount of power right from the start as the previous tuner of this car had it running on a bit of a knifes edge. 9 counts of knock and bit if a lean AFR at peak torque forced me to make the tune more conservative by adding a bit more fuel at peak torque and pulling timing in a few places. I barely had to adjust the AFR up top during the bleed, it was pretty much right on target where we like to tune these cars anyway. End result is a car that runs superb and is completely drivable right now. Down ~15 hp/10tq, but not because of the valve and bleed setup. Customer is more than happy with that as 300 driveable HP is better than 315 that you cannot use at all. He even stated he's not capable of driving the car for all it's worth so 15hp isn't going to affect much for him.

-Regards,
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Old 01-31-2008, 04:01 AM
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Hmm...interesting. But I still don't get how the bleed helps transient bucking at low load conditions? I mean, if BOV only pops open above 24 psi, it should be shut when bucking occurs as I assume you don't reach 24+ lbs when bucking happends? Thus car would react the same when it comes to bucking with or without the pop-off as bleed is only active at WOT, no?

Regards,
Goran
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Old 01-31-2008, 04:25 AM
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Adam, happy to hear all is OK for now. However, if the issue is compressor configuration related ambient pressures and temperatures will trigger it again. What works in winter testing may go way when summer temps return with very high track surface temps.
I maybe restating something that is obvious to you so please don't take offense but dynos are good for documenting baseline power but are not used to identify, test and verify fixes for these road condition problems.
Email if you still want to investigate inducer porting.
Old 01-31-2008, 05:36 AM
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Hmm...interesting. But I still don't get how the bleed helps transient bucking at low load conditions? I mean, if BOV only pops open above 24 psi, it should be shut when bucking occurs as I assume you don't reach 24+ lbs when bucking happends? Thus car would react the same when it comes to bucking with or without the pop-off as bleed is only active at WOT, no?

Regards,
Goran

I haven't quite sorted this out yet myself. The only conclusion I come up with so far is that the valve (controlled by the MBC) is acting similar to a wastegate in that it's opening transition starts well before the actual target boost level is achieved. It may be opening just a minute amount under the low load conditions that it "shifts the compressor map just enough to stay out of surge. this may be due to the fact that the boost signal it receives to open up is a boost only source, directly off the compressor housing. Even in a neutral rev this turbocharger can build abut 7psi of boost, so I imagine that there is some building of low boost at low throttle inputs even though the engine isn't calling for it. I would bet that I could find out by tapping a boost gauge source between the compressor outlet and IC inlet to see if there's any residual pressure in there during cruise/low throttle input. That's where the valve boost source is essentially pulling from.

I still get an ever so slight shudder at VERY low throttle input with engine rpm, say on a long flat cruise, in between ~3hg and ~2psi boost. I think it's just a working area of the compressor map that I just can't "get to" and tune out with this type of setup. This happens once in a blue moon now and is a far cry from what it used to be. It'll never happen out on the track running 10/10ths as it stands now. In all reality I'd say I've tuned this out of 99.98% of the operational area of this motor/turbocharger which to these Evo's owners is a second Christmas day The good(and quite surprising)thing was it had no huge effect on power during the bleed. These cars using this turbocharger fall off up top like a lead balloon anyway.

I'm working on an ported shroud housing right now. If it does what I'm thinking it'll do, in it's own right it should stop this problem altogether w/o the need for the bleed setup I have now. Effectively widening the cross section of the map a bit more to keep the compressor out of surge(in theory)

Goran I really appreciate your insight on this and efforts to help me along in solving it. Not many people are so persistent. It's a good thing Thanks!

Regards,

-Adam
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Old 01-31-2008, 05:46 AM
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Old 01-31-2008, 05:49 AM
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