Intake manifold butterfly with Turbo 6A12

[d_dan]

Hey guys,
I got my Turbo GPX running but on the first run the power numbers were way down. I mean less than a standard FTO numbers.
It made 160BHP and 170Ib/ft @ 0.5bar

The Inlet manifold has this butterfly that controls the airflow through the plenum that would open an close to direct the air flow based on where we wanted the power along the curve.

Is there a chance that this is causing an air blockage and causing the serious drop in power?

IMG_0893.JPG (277.93 KiB) Viewed 2494 times

[bjk]

Doubt it, I don't think I've ever seen anyone else have issues with them.

Did you dyno the engine beforehand?

[Vectose]

What's controlling the valves?

[d_dan]

Did you dyno the engine beforehand?

Before turbo kit was 198BHP(sorry dont know what that is in KW) then first attempt to turbo it was 160ish and second time around again 160.

I was doing some reviews of the work I had done. First time round the engine wasn't forged and I used a decompression plate to reduce the compression. To counteract the rise in the heads and the adjustment to the timing I had customs vernier cam gears made up.
On the Dyno that time the engine was once again down on power but before we could identify the cause the engine spun big end bearing's in the Dyno, forcing the new rebuild.

I'm thinking giving that these were two very different builds were the engine was rebuilt, a new turbo etc. it's very odd that a similar issue would show up both times.
One of the only parts that was used on both builds was the vernier cam gears as even the ECU was changed. That maybe the angle that the verniers came with have the valve timing thrown off as they were never adjusted from what I can tell.

If the inlet and exhaust were open at the same time I'd loose compression or if the exhaust port was open prematurely I'd loose power so maybe??

What's controlling the valves?

I swapped over to an Autronic SM4 for this build so I assume that's now controlling everything. But I'm not sure how it all works ECU's are my weaknesses

[bjk]

I'm assuming that 198hp is an estimated flywheel figure? Sounds like there's a lot more going on than just the inlet flaps though, beyond my paygrade I'll let Vectose fill you in on the details of how they work, but I'm assuming he's going to suggest that they might not be set up to function properly (might be fully open or closed). I don't know if they'd make as much difference compared to if the verniers were not right.

[d_dan]

Yea, I was wondering if I've gone turbo do I really need them maybe I could open or close them and test.

[bjk]

From my limited understanding, they're more useful in N/A applications to change air velocity over RPM; long runners for low and mid-range, short runners for top end. Much like MIVEC, there will be a point at which it is beneficial to switch from one to the other to gain torque. Not quite apples to apples, but I saw a vid semi-recently regarding this on an MX-5 (as Mazda uses the same principle in their VICS system). On the dyno with an aftermarket ECU fitted, they did one run with them shut, one with them open, and used that to determine the set point. For boosted applications though, I think people tend to remove them or fit manifolds that aren't equipped with them. Suspect it could be similar here.

I know Vectose has mentioned that a lot of ECUs don't have the capacity to properly engage both the MIVEC and butterfly system due to how the latter operates, and that usually it's easier to leave the stock ECU inline to manage the butterfly valves.

May even be worth putting the stock cam gears back on to see if that makes a difference?

[d_dan]

Yea I was reading about this last night and the GTO is a good example it's the same engine but has a NA and Turbo variant and as you suggested @bjk the NA has the butterflies but the Turbo does not so that sets the tone for removing it.

I got in touch with Autronic who said that I could control the signal for the valves and build a table with RPM Vs load and set it to one of the output connections to control the variable induction control servo. I'll need to ask can I control this and mivec at the same time if no is the answer the. The butterfly is deffenitey coming out.

Also going to remove the Verniers and start with as few changes as possible and work from there.

[d_dan]

Yea I was reading about this last night and the GTO is a good example it's the same engine but has a NA and Turbo variant and as you suggested @bjk the NA has the butterflies but the Turbo does not so that sets the tone for removing it.

I got in touch with Autronic who said that I could control the signal for the valves and build a table with RPM Vs load and set it to one of the output connections to control the variable induction control servo. I'll need to ask can I control this and mivec at the same time if no is the answer the. The butterfly is deffenitey coming out.

Also going to remove the Verniers and start with as few changes as possible and work from there there's just too many variables right now.

[spetz]

You can remove the stepper motor that controls those butterflies just to test the theory. They spring to a "naturally open" state from memory.
When you put that motor back, you need to put it on at a 90 degree angle, then rotate it to close the butterflies and then bolt it onto the plenum.

Basically they spring open, but when you attach the motor back it needs to hold them closed.
They operate at above 4,500rpm when they open up

[Tomorrowcalling]

I can confirm that the valves spring "Open" and that "Open" is where you would want it positioned at high rpm.

But the motor is not a stepper motor, it's a DC motor with an attached pulse generator.

The motor is powered by connector A-03 in the wiring diagram, Applying +12V and an earth to the terminals as shown below will open the valve. Reversing the connections will close it, the valve doesn't need to be and probably shouldn't be powered continuously

I use a Arduino to control the valve on my Stratos. The control logic is roughly as follows.

The ECU (Link) commands the Arduino to open the valve at a set rpm

The Arduino applies power to the DC motor and monitors the pulses from the pulse generator (pins 2 & 4 on connector A-02)

when the pulses stop, turn off power to the motor

Do the same with the polarity reversed to close the valve

Screenshot 2021-08-19 174124.jpg (41.26 KiB) Viewed 1857 times

[d_dan]

AHH interesting so I need to actually open and close it it's not like 12v and it opens and no power and it closes.


Has anyone any input on what it would be like if I just removed the butterflies?

[Tomorrowcalling]

AHH interesting so I need to actually open and close it it's not like 12v and it opens and no power and it closes.

Correct.

If you're turbo charged, I'd be inclined to just lock them open, or dismantle the header and remove them, even a small amount of boost will probably override the increase in volumetric efficiency that variable length inlet runners give you

A small confession - I've been driving around with them working in reverse and the car still goes pretty well!

[d_dan]

If you're lowering it via an Arduino do fix that would bit not be as simple as to just swap the jumpers around for open and closed?

Yea I've gone the route of removing the butterflies but I have an extra plenum here that I might try to control.

[Tomorrowcalling]

If you're lowering it via an Arduino do fix that would bit not be as simple as to just swap the jumpers around for open and closed?

Simpler than that, I can just change the logic in the Ardunio software , The hard part is reaching the programming port. I've got to remove a section of interior trim which is a pain in the ass, there's another job that needs to be done at the same time but I'm waiting on a part to come so reprogramming the Arduino has gone on the back burner until then. With NZ in level 4 lockdown it's not like I can go for a drive anyway