I think I need a visual, I don't see how you will control boost effectively.

I'll do a diagram later . But yeah -poor boost control is the what could sink the idea . I think I have it covered but there is still plenty of risk there .

With a 4psi spring and push pull you can set the controller at 10psi, and when it hits 10 psi it can go all the way full open with the WG if that's what it needs. If the center port WG full open can't control your boost pressure then you have way undersized your turbo. Just think about how small the WG hole is on a stock Greddy, and that tiny thing controls boost...

The problem with plumbing and WG sizing is that a full pneumatic system can't fully open the wastegate at a set pressure. If it's set to 10psi it will crack sometime before 10psi and then get some fraction open at 10psi to maintain pressure. You have to oversize the wastegate because it can never fully open where you need it to.

It's gunna be a 'suck it and see' exercise .It would seem starting with a small spring will be the way to go to avoid boost spikes . I have a sneaky feeling boost control will actually be better than a conventional setup though.

Just tried the vac. line on it with a 6psi spring in there . Almost opens it but not quite at idle . Opens at anything more than idle vac. so looks like a good starting point as exhaust pulses should be enough to open it at idle as well.

With such a quick spool, are you worried about a massive power "hit" like on the original Greddy kit? The dyno charts I have seen made me concerned for the life of my transmission.

That's not going to work very well. With a 6 psi spring you would normally be limited to around 12psi when exhaust pressure will start forcing open the valve, but with vacuum locked in on the top it will drop the max pressure you can run down to almost nothing. You need a 4 way solenoid to do this right.

yeah ... I can see that now . What I might try is a modified check valve that doesn't close till some boost starts to flow passed it . I would prefer something quite simple and seemless rather than an on/off solenoid doing this job.

Possibly not with this setup as pressure at WG may well be way less than on the turbine side.

You're making the same incorrect assumption as the Renesis header theorists. I had it all typed out and then f'ing lost it. Will post the explanation later when I have more time.

Please do. Considering the WG does not need to handle anything close to full exhaust flow (depending on turbo sizing) I don't see a problem with the use of the siamese port for the WG.

It's not an on off solenoid, it's a boost control solenoid. It happens to have 4 ports, but it can handle PWM. The only complicated part is a little extra tubing and in my case a couple check valves with a tee. Look up push pull boost control.

Would you mind going into how this functions a little more please . I'm struggling to get my head around it .
I presume when it's off you have vacuum to top port of WG but what is happening when it's cycling ?


Edit :
I'm sold ... got one on order

The function is pretty simple. You put high pressure on the top of the valve and low pressure on the bottom and it stays closed regardless of boost pressure. You put low pressure on the top and high pressure on the bottom and it stays open regardless of boost pressure.

All the check valves do is allow the low pressure to be at a vacuum (when the throttle is shut) which is enough to overcome around 7lbs spring pressure. It works just as well with the low pressure side directly to metered air, or even a non metered atmospheric vent.

Oh and to have it open the WG during cruise you need a boost controller that can do that, or a relay wired into the controller. Most boost controllers will try to keep the WG closed until they are at set-point.

Checked my Greddy EBC ... It doesn't activate the valve closed till it sees a little over 1psi so it will work without any extra relays etc.

isn't it good for spool to keep the wastegate closed at light load.

I very much doubt it would be noticeable

When Mazda first tried the side port design it was only with the two end ports. What they discovered was gasses from the center iron side were not evacuating effectively. So they added the center port for this purpose. It was never intended to be a full flow port like on the end irons, but rather an additional relief port. They also had to add in the divider plate to minimize cross flow & heat between the two rotors. As a result, the center port flows considerably less than the end ports and this has pretty much been overlooked in every header design; equal length, long tube, etc. Even if you could build a header capable of scavenging on a zero overlap Renesis (you can't, dummies) if you use the same diameter tube on the center port as the end ports then you are effing up the timing of your scavenging design right off the bat. It doesn't flow the same as the end ports, not even with the combined gasses from both rotors.

The question here is will it be capable of enough flow to properly control boost as a dedicated wastgate port. Brettus has wisely chosen a 1.06 AR divided turbine housing which will help flow at the expense of low rpm response. I'll be surprised if it has full boost by 3500 rpm. Partially because of the AR even if divided, but partially because of why the center port exists; it won't be clearing out gasses on the center iron side during spool-up because the wastegate will be closed and not allowing any center port flow. There will be an efficiency issue with the center port closed off. The magnitude is difficult to assess though.

I'm skeptical that the center port has enough flow potential to effectively control boost on it's own. As a restictive port it will potentially be self defeating for wastegate control. More backpressure can force more flow through it, but that same backpressure is also spooling the compressor wheel to pump out more boost. To be effective it must offer the path of least resistance *for both rotors*, which IMO is questionable. So potentially you are in an escalating loop that may prove difficult to control.

I could be wrong though. I only call you out because you presented it almost as a fact that it can flow enough without any room for doubt or error. That's pretty typical for you (Harlan) when making theoretical assertions. The path in reality is not always so clear.... (insert excuses & work-arounds here)

Well thanks for calling me out personalty. I do appreciate the attention.

Now I don't know where the disagreement here started... IF the center port is to minimize EGR on an NA engine which makes a lot of sense then how does that change this discussion? Sure this design might have a bit more EGR when the center port is closed, and sure the WG won't be able to flow as much as it would off a normal port, but in the end does that even matter? I still don't think so, and I'll wait for it to be proven either way.

You accuse me of making assumptions, but right now you are stepping pretty far out with yours. At least this time you are bringing your assumptions to the table, albeit without actual facts.

Subtle difference -->
Otherwise sorry, I generally ignore same like in your own thread but this time I did not choose to do so ...

You didn't leave much wiggle room in this statement, and you must have read my mind to know what I was assuming and at the same time know I was wrong.

I'm more than willing to debate the merits of an idea on theory or on actual testing, but please stop mind reading.

guess I hit your tender spot to the point you're not thinking clearly, ok then ...

How do you know this ?

Team , I think (and hope) the center port flows somewhere between 34-40% of the total flow from an NA engine . Here is my logic ........

Many years ago Hymee showed a renesis on the dyno and the only tube that was glowing red was the center port tube . That led me to make one (fairly big) assumption : that the center port tube flows more in total than either of the side port tubes.
For that to happen ... the individual Siamese port on one rotor must flow more than 34% of the total for that rotor . Or in other words the two ports combined are more than 34% of the total for the engine which leaves 33% for each outer tube .

It is also safe to assume that the individual Siamese port flows less than the other port. Only 5% less would seem unrealistic ...............

Hence my guess ........ 34-40%

If I'm right on that ... it is right in the ballpark for what I expect the wastegate to flow.
X fingers!

This is just a shot in the dark, I know the Siamese port has been fiddled with before. Could you fab up a full divider? I know it would play hell with header/manifold design, and that "divider" piece would get hot as hell, because it's constantly exposed to exhaust gases, and never gets a chance to cool?

The first design I thought of had a fully divided tube and even a balance tube from the other port. I went away from that idea when I realised that the amount of back pressure from the wastegate and downstream of it should be only a few psi . Plus there is more flow potential by opening up the port rather than closing it in.

Ok how about a little problem.

Lets say exhaust pressure in the housing is 2psig, and going out both exhaust ports it drops to 0psig. The pressure drop across each port (and the associated exhaust pipe) is 2psi. At that 2psi there will be a certain amount of flow through each path.
Lets say an 80/20 split between the main and siamese port.

Lets say you mount a device (*cough* turbo *cough*)that creates backpressure on the main exhaust port, and now instead of 2psi in the housing you have 8-10psi. If the siames port is fully open will that create more or less flow through that port in relation to total flow?

If we had real numbers for exhaust housing pressure and turbo backpressure we could even figure out how much different the flow rate would be.


Oh and the reason why the center exhaust pipe glowed red when the others don't is there is no real time for it to cool off between exhaust pulses like the other two ports.

Don't know if this was supposed to be a rhetorical question or not.... but of course it will increase the flow through the siamese port as flow will direct more at the path of least resistance. Theoretically with more pressure in the housing it will increase exhaust velocity through the siamese port equaling greater mass flow rate.

You think 0.0067 seconds is long enough to cool down ?

two pipes the same diameter and wall thickness are flowing hot gas from the same source ... one is glowing red one isn't .
The possibilities:

*the gas is hotter in one than the other
*one is flowing more gas than the other


Pick one ....