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Run dual 44s here, 7lb springs, dubious of comparing flows across brands, but very similar size turbo. It's been tuned to be capable of running at that minimum pressure for wet events and is consistent going by dyno print.
If that existing pipework you have is 1 1/2" off the WG, that DP(?) doesn't look particularly large, and with both joining at near the same point normal to flow probably less than ideal when combined area is not much less. I also see that Canadian car mentioned in the earlier link now has a 90 degree entry on it's latest iteration too. Plumb back here is in the 35 and 75 degree range from memory.
One consideration, the tighter you get on entry the more difficult it is to weld the inside corners, hail marys required sometimes and possibly part of the reason the mig was wheeled out in that first abomination.
Your WGs are a little bigger than mine (44 vs 40mm), but I suspect your recirc piping has much better flow, and probably dumping into a larger DP than my setup. My WG dumps start out at 1-5/8" and expand to 2" piping; the problem I think is I've got too many bends to make it all fit, and those 90* bends into the DP is probably creating lots of turbulence & back pressure when the WGs open up. My DP is just a 3" diameter, going into a 3" resonated mid-pipe section. If you have pictures handy of your setup, please share - might be useful for inspiring a local fabricator if I decide to spend the cash on v2. Here's a picture of my piping, with the parts laid out on the floor roughly how they would be assembled & joining up with the WGs & turbo prior to me wrapping them with lava wrap.
Originally Posted by Howard Coleman
"limit boost on the intake side via the DBW throttle."
that should work fine and give you what you want for now
Kind of, but not quite as good as I'd like.... From road testing, I've found that the DBW approach works great for managing boost creep, which tends to ramp up the boost slowly. The DBW catches it, boost rapidly drops when the throttle pulls back, and then when boost falls back below the threshold again, the throttle comes right back to where it was - I'll feel a power delivery hiccup but that whole cycle happens in less than 1 second, and I might get this cycle to repeat a few times if I stay on the throttle. The problem is this DBW approach fails to respond quickly enough to intervene during shorter duration boost spikes that ramp up a lot quicker than a boost creep situation.
Case in point - I had the Link's MAP engine protection limit set to intervene at 11.5psi MGP, using the "rotary specific" basic fuel/spark cut mode. Per my convos with the Link engineering folks, this MAP limit has a very fast reaction time, sampling MGP/MAP at a rate of at least 500Hz or so, and it actually starts its intervention at a pressure that is 10KPa LOWER than the limit you set, so in my case, 11.5psi - 10KPa = approx. 10.5psi. My DBW based soft boost limit works by using a virtual AUX to monitor MGP, and when my 10.3psi MGP set threshold is crossed, it commands the switch to my alternate 1/2 throttle DBW mapping. In theory, that means that the DBW based protection mechanism should always intervene before the hard MAP limit (rotary specific fuel/spark cut) intervenes, but that's NOT what happens during a short duration boost spike. For example, if I'm entering a highway in 3rd, say from a rolling start around 50MPH, still in vacuum & revving at roughly 3~4K RPMs, then floor it as soon as I have a clear lane, the boost ramps up so rapidly that the hard MAP limiter (fuel/spark cut) will intervene before the DBW method does. This is most likely because the ECU is sampling MGP/MAP at a much lower rate, say less than 100Hz for the virtual AUX than it is for the hard MAP limiter.
Since the hard MAP limit is rougher on the car (i.e., it causes nasty exhaust back fires) than the DBW based method, as a temporary fix I raised the hard MAP limit up to 15psi MGP, and so far it hasn't intervened yet in similar boost spike inducing situations. But if I run ECU logging at the max sample rate, the logs are telling me that the boost can exceed my DBW based 10.3psi MGP limit, spiking up to somewhere less than 14~15psi (the hard MAP limit) for at least a brief instant of time without the DBW protection mechanism intervening.
Another suggestion would be to make the downpipe a smaller size at the turbine to bias flow/pressure to the WG and then expand it to a larger or existing size at the WG merge to handle the total merged flow. The general method here on the forum seems to be to add a restriction further downstream, but biasing it between the turbine and the merge then imo it will require less overall restriction in the exhaust system to accomplish the same effect.
Since the merge needs to be reworked, then reworking the DP to that point is possibly something worth considering.
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Another suggestion would be to make the downpipe a smaller size at the turbine to bias flow/pressure to the WG and then expand it to a larger or existing size at the WG merge to handle the total merged flow. The general method here on the forum seems to be to add a restriction further downstream, but biasing it between the turbine and the merge then imo it will require less overall restriction in the exhaust system to accomplish the same effect.
Since the merge needs to be reworked, then reworking the DP to that point is possibly something worth considering.
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That makes sense too. After all, WG function is basically a balancing act between pressures - (1) Exhaust pressures acting on the front and back sides of the WG valve, (2) WG spring force acting to keep the WG closed, and (3) boost pressure and/or barometric pressure on one or both sides of the WG diaphragm, acting to open or keep the WG closed, depending on how you setup your boost control plumbing & solenoid(s).
Another idea I've been kicking around is to perhaps try some sort of muffler/resonator on the dump tubes, and close off the holes in my existing DP where the recirc pipes enter it. It would probably be louder than the existing setup when the WG crack open, but should be much less obnoxious than open dump tubes. There might be enough room to fit something like that, but ground clearance may be an issue.
I had the exact same wastegates in a plumb back set up off of an efr8374 1.05 eg and it held 7psi like a rock off 7psi springs, was uncanny. Simple difference im guessing was I finessed gentle angles instead of dumping back into the down pipe at 90*. Same thing with wg priority at the manifold.
edit: that said, I virtually never ran it at 7psi though apart from during break in, and certain circumstances, was nice like that though, almost like N/A power delivery, except,, more of it. Why can't you just set it at 11psi and leave it there as your lowboost setting? Apologies if that has already been covered.
Last edited by WANKfactor; Nov 25, 2022 at 08:22 PM.
Pete, would it be O K if i borrowed the DP pic in post 27? it would be helpful in my System Setup Section for my site in the how not to do things (i know you didn't do it, your welder did.)
it might save some peeps heartache down the road.
while there are various options as to how you might band-aid your situation i suggest you bite a second bullet and find a good welder and fix it properly.
you have a nice car and it has a single serious malady. consider the backpressure.
Pete, would it be O K if i borrowed the DP pic in post 27? it would be helpful in my System Setup Section for my site in the how not to do things (i know you didn't do it, your welder did.)
it might save some peeps heartache down the road.
while there are various options as to how you might band-aid your situation i suggest you bite a second bullet and find a good welder and fix it properly.
you have a nice car and it has a single serious malady. consider the backpressure.
your engine will thank you.
Sure Howard, hopefully someone else can could learn something from this mess! Finding a skilled fabricator for something like this isn't easy - what's on there now is actually version 2 from the same shop. Version 1 was an even worse pile of steaming poop, so they agreed to do version 2 that you see here for free.
So it's a tough call - another round of fabrication would be very expensive, so I may just have to live with higher boost on the low end. I ordered the 3 & 5 psi springs to test with, if either of those gets me to a consistent low boost level of 10~11psi on springs alone, I'll call it good enough, and tune on for higher boost, up to about 15ish psi with the boost controls enabled. Based on the fact that this turbo spools up so fast & strong, and based on the kind of numbers it wants to see in the VE table under boost, I don't think exhaust back pressure is an issue when the WG's are closed - it certainly may not be optimal, but from the turbo on out to the tailpipe it seems happy. It's only when the WG's crack open that it appears the WG dump piping gets pressurized from the back pressure, which is fighting with proper WG operation.
"muffler on the dump tubes"
i recently read a post by someone who attached some piping and a muffler on each of his dump tubes. he found the sound was way too loud and removed them and moved on to Plan C.
thanks
Last edited by Howard Coleman; Nov 27, 2022 at 08:10 AM.
the WG spring change isn’t likely to have any positive effect over what you already have
So then the easiest way to address it is probably to put a gasket with a smaller thru-hole downstream in the exhaust system. Which as I mentioned is a common “fix” on the forum. It will definitely be less back-pressure in the upper rpm range to handle it between the turbine and wastegate juncture, but not as simple or cheap.
As you mentioned; given the turbo, turbine housing and boost pressure goal it’s unlikely that the emap is going to be excessive. While lower emap is always better from an engine loading perspective, there’s a reason the flow is going to the turbine rather than the WG; it’s always going to bias towards the path of least resistance. Since your goal isn’t to maximize power then emap becomes less of a concern within reason.
dumping anything exhaust related under the chassis; muffled or not, is always going to sound loud in the cabin
next easiest way would be to cut the downpipe in a straight section before the WG merge and cut/grind a reducing cone to just fit the tube ID, then weld it all back up with the cone inside. That doesn’t require much fabrication skill.
in fact, you might even be able to do that at the DP entrance from the turbine without welding it in place. That’s likely to depend on the DP diameter and cone angle. If so, that would allow you to experiment with cutting the small end of the cone back to only add as much bias as needed to achieve your goal.
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Your WGs are a little bigger than mine (44 vs 40mm), but I suspect your recirc piping has much better flow, and probably dumping into a larger DP than my setup. My WG dumps start out at 1-5/8" and expand to 2" piping; the problem I think is I've got too many bends to make it all fit, and those 90* bends into the DP is probably creating lots of turbulence & back pressure when the WGs open up. My DP is just a 3" diameter, going into a 3" resonated mid-pipe section. If you have pictures handy of your setup, please share - might be useful for inspiring a local fabricator if I decide to spend the cash on v2. Here's a picture of my piping, with the parts laid out on the floor roughly how they would be assembled & joining up with the WGs & turbo prior to me wrapping them with lava wrap.
Couple of computers ago and anything I might have saved somewhere, is for a shorty manifold and with the additional twist and turns of RHD, so not entirely applicable anyway.
Those connections from the wastegates, a mix of schedule pipe and tube? I wouldn't expect those few bends to be a big issue, the side by side join at the DP - well. Looks like the fabricator failed on petitioning his favourite diety with the reducing cones and stepped diameters though!
This might help on inspiration.....and a BW to boot on the long manifold.....appears to be a 3 1/2" downpipe eyeballing it??https://www.facebook.com/Turblown/photos/a.475546083684/10157627247308685/ You could also check this vid. Again RHD, but long manifold and much more convoluted https://www.rx7club.com/single-turbo-rx-7s-23/selecting-single-turbo-1157889/#post12526727
Couple of computers ago and anything I might have saved somewhere, is for a shorty manifold and with the additional twist and turns of RHD, so not entirely applicable anyway.
Those connections from the wastegates, a mix of schedule pipe and tube? I wouldn't expect those few bends to be a big issue, the side by side join at the DP - well. Looks like the fabricator failed on petitioning his favourite diety with the reducing cones and stepped diameters though!
I don't think there's any schedule piping on my current WG connection sections, just mandrel bent tube sections, some straight tube, cone expander & flex sections, V-bands on each end. My current DP is 3".
That's a pretty cool solution on the HPA video. Basically they managed to cram an entire 2nd exhaust system with mufflers/resonators dedicated to just the WG's all the way out to the tail.
the WG spring change isn’t likely to have any positive effect over what you already have
Why? Is that because exhaust back pressure acting on the back sides of the WG's would be unchanged, and is still trying to keep them both closed?
Originally Posted by TeamRX8
So then the easiest way to address it is probably to put a gasket with a smaller thru-hole downstream in the exhaust system. Which as I mentioned is a common “fix” on the forum. It will definitely be less back-pressure in the upper rpm range to handle it between the turbine and wastegate juncture, but not as simple or cheap.
^That would be cheap & easy, but if the restriction is added downstream past where the WGs merge into the DP, wouldn't the resulting increase in back pressure be applied to the WGs and to the turbine be roughly equal? I thought what we're trying to do is get a differential pressure - reduce the back pressure acting on each WG relative to the turbine by increasing back pressure acting on just the turbine to persuade the WGs to open up?
Originally Posted by TeamRX8
As you mentioned; given the turbo, turbine housing and boost pressure goal it’s unlikely that the emap is going to be excessive. While lower emap is always better from an engine loading perspective, there’s a reason the flow is going to the turbine rather than the WG; it’s always going to bias towards the path of least resistance. Since your goal isn’t to maximize power then emap becomes less of a concern within reason.
dumping anything exhaust related under the chassis; muffled or not, is always going to sound loud in the cabin
next easiest way would be to cut the downpipe in a straight section before the WG merge and cut/grind a reducing cone to just fit the tube ID, then weld it all back up with the cone inside. That doesn’t require much fabrication skill.
in fact, you might even be able to do that at the DP entrance from the turbine without welding it in place. That’s likely to depend on the DP diameter and cone angle. If so, that would allow you to experiment with cutting the small end of the cone back to only add as much bias as needed to achieve your goal.
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^Those are two great ideas, and since both are upstream of the WG merge, they should increase back pressure on the turbine relative to the WGs to get that differential pressure going. I especially like the insert idea of dropping a cone in the turbine end of the DP. Will have to take some measurements to see if one of these cones will fit, they have 3" to 2-1/2" SS cone reducers that are only 2" long overall - https://www.verociousmotorsports.com...ntric-reducers.
Besides the noise, the other issue with a small muffler/resonator dump underneath is it does nothing to stifle the stink/fumes.
wrt the gasket fix; I’m just telling you that’s how it’s been done here. Seems like it’s typically a gasket with a 2.5” ID hole in a 3” tube flange, but just my recollection. You can search it to verify. Likely just backing the entire thing up accomplishes the same thing, but with a bigger emap penalty for the obvious reason.
you also have my thoughts on what might be a better way to address it. If I had to take an initial swag at it; cutting a standard 3” x 2.5” reducer back to 2.75” (or ordering it specifically to those dimensions with no straight end on at least the inlet side from SPDExhaust etc, and you can get different taper angles as well to control length) is where I might start.
in fact a reverse cone style for it might be considered, just a matter of how much you want to spend or chance on
SPDE can likely even provide it in T321 stainless for handling the heat
ran across a pic that shows the Ferrari F40 setup, and thought it looked rather like Howards setup....
F40 is right after the F1 turbo era. also notice that the header is insulated (i think that is what that is)
also notice that the header is insulated (i think that is what that is)
Enzo did that at least as far back as the 70s, using a gas welded aluminum case stuffed with white fibrous stuff (supposedly not asbestos!). Didn't appear to be wholly effective, still cooked the cabin - with the engine, east-west rather than longitudinal - and fuel fires were hardly infrequent.
Originally Posted by Pete_89T2
Now why the hell did my fabricator guy not know about these problem solving parts?
Probably needs a bit of work on the lips to maybe get it to fit, unless you change exhaust diameter. Should make manipulating the torch easier and you'd hope for better welding effort.
they could just angle cut some straight tube sections to slice & dice whats there already to oblong-angle the opening as well. Then no need to rework the WG piping.
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I didn’t know about those merge pieces either though, looks like a custom offering by a company I wasn’t aware of. Also not sure why anyone chooses T316L over T304 either, not really of consequence on an exhaust application. If anything it should be T321 for high temp strength and longevity purposes.
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Help me interpret static test results on WG operation
So today the 3lb & 5lb springs came in, and I just pulled off the WG dump pipes so I can do another static test of my WGs with the existing 7lb springs, before changing out to the new springs, just to verify that my WGs are working properly and not sticking shut. Here's how I rigged up the test:
- Connected my compressor to a low pressure regulator & gauge. This setup lets me vary & regulate the air pressure accurately between 5psi ~ 30psi while the gauge lets me accurately monitor what the WG's are seeing as a pressure input.
- Connected the regulator output to the boost pressure hose going to my boost solenoid. This way the test includes all of my plumbing, and I can see if the WGs respond in synch to pressure input. My boost solenoid & plumbing is set up so the "bottom" diaphragms of each WG see boost pressure from the compressor if the solenoid is not energized, and top WG diaphragms see atmospheric pressure. See schematic diagram of my WG plumbing below.
So in theory the WGs should start to open right around the 7psi spring tension, but in reality since there's no exhaust pressure helping them along in a static test like this, they should open at a pressure somewhere higher than that - the question is, how much higher is considered "normal" here?
During the static test, I observed that the valve seat on both WGs just starting to crack open slightly at pressures between 10~12psi, but they would not open fully until I had the pressure cranked up to at least 25psi. Not sure if this is a good result for a healthy set of WGs, what do you experts think? More troubling to me was the way they opened - it wasn't a smooth linear opening progression with slowly increasing pressure, but more of a sudden discrete "pop" open, with a bit of a creaky sound to it.
Update to static test - this time with the 3lb springs
Update on my static test results with the new 3lb springs:
- Now both WGs just start to crack open at 5~10psi (lower than before with the 7lb springs - good), and are fully open at 15psi vs 25psi (also good). Also noted the opening behavior was smoother and more linear relative to increased/decreased air pressure. Hope the weather stays good the next few days so I can road test the new setup.
So I got out yesterday to do a quick pull to check boost response with the new 3lb springs. Unfortunately traffic prevented me from doing any pulls up to 100% throttle yet, but based on prior logs at similar throttle openings & road terrain/loading, the initial results indicate I've got boost under control now. In the 3rd gear pull, boost maxed out at 5.1psi MGP. Also did a bunch of repetitive short pulls in 4th & 5th gear that in the past would have induced it to creep to the moon, and they didn't get past 5psi MGP either. Plus the ambient air temp was about 35*F, so it was cold and would I have expected more creep with the colder, dense air. Screen shots of logs in 3rd & 5th. Yellow cursor is at point where boost maxes out.
^This is the 3rd gear pull ^And here is a 5th gear pull, attempting to induce some creep.
plenty to be discerned here, thanks for sharing.
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You're welcome, hopefully someone else can learn from it. Weather here is turning cold, and they salted the roads for the 1st time this winter, so further road tuning will have to wait until winter hibernation is over. I'll call this job done after I can get some good 100% throttle pulls, but doing a little before & after comparative log analysis under similar conditions is telling me that the data is trending in the right direction....
This next log screenshot is with the 7lb WG springs when it was still boosting to the moon. The yellow cursor in this log is at the point where boost hits 10.2psi MGP, throttle is at 46% and IATs were at 64*F. You can also see in this log that my DBW soft boost limit had just triggered (look at bottom of parameter list - "E-Throttle Active Table = Table 2"), but the DBW throttle hasn't reacted yet, as TP is roughly = accel. pedal position (AP). if you could move the yellow cursor 1 more sample to the right, you'll see the throttle drop to 1/2 of the accelerator pedal position, and MGP dropping to about 9.5psi or so.
^This is the "before" data, 3rd gear pull with the 7lb WG springs
And here's an "after" log with the 3lb WG springs. This was another 3rd gear pull, on the same stretch of highway where I did the above pull, so same terrain. The yellow cursor in this log is at the point where boost hits 6.5psi MGP, throttle is at 55% and IATs were at 54*F. So mostly the same conditions as the "before" log, but with a little more throttle and slightly cooler IATs, boost is now controlled down to a pretty steady 6.5psi MGP
^Here's some "after" data, 3lb WG springs, 3rd gear pull
This last an "after" log with the 3lb WG springs is a 5th gear pull, attempting to induce some boost creep. The yellow cursor in this log is at the point where boost hits 6.2psi MGP, throttle is at 65.9% and IATs were at 54*F.
^And another "after" data set, this time in 5th gear, lower RPMs & more throttle, attempting to induce some creep
