ACR_RX-7

iTrader: (1)

That is one way of doing it, absolutely. I will say that I was amazed at how fast my Dodge spooled with an MBC. I was totally unaware that the PCM was overriding it that much to prevent that. My BOV is built into the compressor cover, much like an EFR. It opens at the slightest lift of throttle, even when around town. My fix for it, in the future, is to upgrade the turbo. Bigger turbo has less surge, but I am far away from that.

Tuning4life

iTrader: (2)

I should clarify what I meant above.

So both the GT3574R and EFR 8374 surge at partial throttle. so when I am driving hard and I am in the middle of a long sweeper, I don't hold the throttle partially open, you sometimes modulate the throttle more/less/more/less with your foot. both turbos would surge doing this, perhaps its at altitude that makes the turbo's do this at part throttle. What I think is happening is when looking at vacuum at altitude the turbo still boosts 3PSI to get to "positive pressure on the MAP" or the zero line in the powerfc or to get to 14.7 Absolute pressure. Most of the BOV springs probably are meant for sea level, so when I part throttle at a few PSI or so and the throttle closes some but the turbo is still feeding the intercooler tract, I don't think the BOV can open at such small pressures, so the turbo surges as the throttle body plates are closed and the BOV doesn't relieve the pressure, on my old turbo is made all sorts of noises but "fought" through it so to speak, the efr wants to kick me out of that region back into vacuum cells more easily at these partial throttle positions when modulating the throttle.

Another thing I noticed is with the GT3574R I could more easily control the throttle at partial boost levels...although it still isn't super refined like an N/A machine, the efr wants to go to upper boost levels so easily with the lightweight turbine wheel.

I still need more seat time and see how it performs outside of mostly tuning the car on straights and playing around.

I need to take it on the turns now that it is tuned.

and don't mistaken what I wrote as bad against either turbo. the efr 8374 just gave me a whole lot of low end power I didn't have, the car is easier to drive fast.

ACR_RX-7

iTrader: (1)

That's exactly what my Dodge did on a MBC. I don't think that altitude should make a difference, since the reference stays the same, regardless of atmospheric pressure. Are you using the PFC for wastegate control? or are you using an MBC? You may want to consider changing your low end boost curve to avoid part throttle boost, or adjust your BOV, if you can to be softer.

BLUE TII

iTrader: (9)

My fix for it, in the future, is to upgrade the turbo. Bigger turbo has less surge, but I am far away from that.

That is exactly wrong. The smaller turbo is less likely to have compressor surge.

Most likely your dodge was just tuned to run stoich and no boost at low loads for fuel economy and now it is trying to run stoich and boost or possibly going wonky trying to correct the AFRs for boost at low loads since you took away its turbo control.

KNONFS

iTrader: (14)

On paper, or proven? Would love to see a sequential 7670 dyno

Wish there was a 7683 EFR option, I guess beggars can't be choosers

lastphaseofthis

iTrader: (8)

from what blue was saying the compressor side is the bottle neck on a 7670, not the turbine...

also i'll post up the 7670 SEQ dyno as soon as a build it. :P

BLUE TII

iTrader: (9)

Wish there was a 7683 EFR option, I guess beggars can't be choosers

lastphaseofthis

from what blue was saying the compressor side is the bottle neck on a 7670, not the turbine...

Yeah, I was able to make peak hp ~6,000rpm on the 7670 and then hold that till just past 7,000rpm where my near near stock closing ports crap out on VE.

I think it is my ports because it was the same time hp started dropping on my same size compressor but larger exhaust wheel 60-1 and no matter what boost I run (meaning at lower boost the compressor would have more flow available if the ports were still in there VE range and flowing.)


The 7670 compressor is "bottle-necked" at 64lbsmin flow which is ~450rwhp rotary.

I still think an EFR 7683 would be bad ***.

I think it would actually spool faster on a rotary with the right exhaust housing and exhaust than the 7670 (from my experience going up turbine wheel sizes on my 60-1) and offer lower exhaust manifold pressures for a happier engine.

ACR_RX-7

iTrader: (1)

You are probably exactly correct. I have not touched the PCM in any way. I just tossed a MBC on because I had one, then went back to stock.

Brettus

If you are running an EBC that activates at around 1psi of positive boost (like my greddy profec does) and you put the signal line to the EBC into the manifold AFTER the throttle, you will get surge as you describe above .
If you put the signal line to the EBC PRE throttle , that surge will disappear and throttle control will improve greatly.

The reason for this is that the EBC needs 1psi of boost before it will activate the 'start boost' function which closes off the wastegate and spools up your turbo . With signal post throttle and at light throttle you are hovering around that trigger point and the wastegate is opening and closing as you modulate the throttle causing surge . With the signal pre throttle any throttle at all will yield more than 1psi and therefore the wastegate stays closed allowing full control via the throttle.

Rub20B

sure but without good BOV this still means closed wastegate an turbo pushing against a near closed throttle possibly causing surge.

Tuning4life

iTrader: (2)

I connected my BOV line between the engine and throttle body. So when the throttle gets cut the BOV opens. this is supposed to be how its installed. If you put it on the intercooler side of the throttle body it won't open the BOV.


At altitude the turbo can boost 3-4PSI depending on elevation to get to a sea level pressure state. Our atmospheric pressure at certain altitudes is between 11.7-10. so I can boost a good 3-4PSI to get to a sea level atmospheric pressure of 14.5ish.


I am guessing the spring on the BOV, and this would include both set ups, could possibly be too strong? Or the engine moves a lot less air flow and I am moving the turbo into its surge line?


I haven't ridden in another rx7 under the same conditions. it basically using high rpms with low boost at part throttle under modulation. its something you would do around long sweepers at high speeds.


I used an HKS SSQV on my first set up and the second I am using the stock BW BOV on the turbo. The tune in this area is around a 13.5 to 12.5AFR depending on the boost pressure. I target 13.0 for a 14.5PSI atmospheric pressure and ramp down in boost.


The turbo definitely wants to boost to max pressure pretty easily, it does not like hanging around part boost level.


Perhaps it could be a TPS issue? I will see how other cars respond before doing anything on my car with the same turbo up here.

Brettus

Didn't mention the BOV. Although adjusting the BOV or using a synapse (like Rub20B mentioned) can help with the severity your problem ,but not solve it.

I'm talking about the line that goes from your manifold to the electronic boost controller .I'm assuming you do have one ?

Tuning4life

iTrader: (2)

yes, the powerfc is controlling my boost and the controller is on the face of the BW turbo using the stock solenoid that came with the BW kit.

The BOV is not tweakable to my understanding. perhaps a different spring is needed? I know BW offers a stiffer spring but not a softer one.

Brettus

And the signal line to the powerfc is coming from the manifold ?

Actually ........... I just realised the powerfc is controlling your tune as well as your boost so you can't do what i suggested . You would need a separate boost controller.

Tuning4life

iTrader: (2)

The boost pressure source for the controller and wasteaget is connected to the turbo itself. the boost controller is in between the turbo and wastegate solenoid. obviously it bleeds some air to control boost higher than the wastegate spring.

I have a separate line running from the UIM between the throttle body and engine to the BOV.

You input a boost number and a wasetagate duty cycle along with it. the duty cycle is how it controls boost, the boost pressure is when the duty cycle "kicks on". the boost controller controls boost by modulating the grounding of the solenoid. so if you don't have 12V going to the solenoid the solenoid is going off spring pressure, the 12V closes the solenoid till the boost setting is reached and the duty cycle modulates from there, the computer tries to keep it as close to the desired setting as possible and this is where you might need to play with duty cycle. If the boost exceeds more than .25 KG/CM^2 (I think that is the units) the computer will do a fuel cut.

I am sure everything is connected correctly and I am sure I am using the powerfc correctly to control boost. This has happened on both of my set ups now using different boost controllers (Blitz spec S and powerFC) but this has nothing to do with it as these aren't doing anything at this low boost level (both are shut).

Brettus

OK ..got it . If you just run on WG spring pressure (boost controller is off)does it still do it ?

Also : is there a pressure line going from the manifold to the powerfc ?There has to be (assuming you are map tuning). If so , this is also acting as the signal line for boost control .

ArmenMAxx

iTrader: (21)

I too am having surge issues at partial throttle lower rpms.

I am considering buying the Turbosmart BOV replacement for the standard BW unit. Anyone have any experience with this in terms of solving the partial throttle surge?

Brettus

Yes ...I have . Which is why i mentioned it above.
I'm not running an efr but the principle is the same for any fast spooling turbo using an EBC.


Boost controllers typically supply power to the solenoid once pressure in the signal line reaches 1 psi . The problem is, at part throttle , you don't get to 1psi in the manifold even though there can be significant boost pre throttle. So the solenoid isn't switched and the WG can open .
At this point there is no power so you open the throttle a little bit more . By opening the throttle you now get 1psi in the manifold but there can be up to 20psi pre throttle and the WG is now closed by the solenoid. This is when you get that sudden uncontrollable surge in power from the accumulated boost reservoir pre throttle plus the activation of the turbo.

Changing the source of the signal line to pre throttle eliminates this as the EBC sees that 1psi much earlier and keeps the wg shut .

This in turn means you don't need to open the throttle as far to get any power , making throttle control much more precise.

Tuning4life

iTrader: (2)

The MAP sensor (GM 3 bar) is the sensor I am using for boost control/engine control tuning.

It's located in the stock location.

The wastegate controls boost and shouldn't have any effect on this. The BOV should be relieving the pressure but its tough because its right at the threshold of boost/no boost. so you have slight boost getting jammed up in the intercooler piping backing up to the turbo and surging/fluttering it. I don't think there is anything you can do about it.

My set up is set up exactly the way you describe. my boost controller is connected to boost pressure at the turbo itself. The BOV is connected in the right spot so when the throttle shuts it immedietly sees vacuum, but the pressure is super low so the spring on the BOV might not open.

My old turbo had more rotational mass so it fought through it better then the lightweight turbine wheel. not that its bad or anything...just what it is.

Brettus

This above tells me that it isn't the way I described .
The map sensor is what is giving the signal to the boost controller which in turns sends voltage to the boost control solenoid.
The problem is that the map sensor will be plumbed into the manifold (as it should be).
This is why i suggested you need a separate EBC that you can plumb pre throttle.

lastphaseofthis

iTrader: (8)

they don't have likes here, so we go with +1

that's some real good info, that i was following and then getting lost in his reply...

ArmenMAxx

iTrader: (21)

My turbosmart EBC also has its boost source right off the turbo. The BOV has its source off the UIM.

The turbo flutters like mad between ~0-5psi partial throttle acceleration. After 5psi its smooth. Its not tuning, its my BOV going nuts it seems. I assumed the turbosmart EFR BOV has a stiffer spring which might help?

Brettus

So the line going to the boost controller on your dashboard (not the solenoid) ....... that is coming from right off the turbo ?

Sorry to labor the point but there seems to be some miscommunication on what is a boost controller and what is a boost control solenoid.

WANKfactor

iTrader: (1)

Just adding my own experience with my efr8374ewg. Im getting that flutter thing a fair bit too. Part throttle, boost/vacuum threshold with some engine rpm on board.
Have a 50mm turbosmart raceport? Bov near the throttle body refferenced to the uim, the efr recirc valve dissabled by way of being looped back to compressor housing.

Im not worried about it. Iv been meaning to hook the efr bov up and dusable the turbosmart, and maybe hook both up together to see which way works better but like i say im not even worried as it doesnt seem to affect drivability.

ArmenMAxx

iTrader: (21)

I see.. No my actual ebc unit is not sourced off the turbo but rather post-tb. I dont have any sources pre-tb, ill have to mod something up or T in the solenoid line.