I understand the purpose of VDI on the n/a motor what with the intake pulse scavenging at rpm, but on a boosted engine is its effect nullified by the pressure in the intake?

I wired mine open initially, but I feel the idle quality and MAP values (at idle) are being compromised. Thinking I'm better off wired shut, Opinions?

**I could've operated all the solenoids with the haltech but chose not to for simplicity. The vacuum chamber is gone.**

 

After running both ways the major difference seems not so much in total vac at at idle. Both run between -.60 and -.70kpa total at idle. The big difference is when you blip the throttle from idle, with VDI open it will go 0kpa very easily and stumble (if using a MAP load based setup). VDI closed blips tend to hit -.20kpa instead. Not sure exactly why. Obviously the stumble created some drive-ability issues, especially for hill starts so glad that's sorted.

This was all done with the SSV wired open.

 

I don't have an answer for you except that I found interesting and relevant:
https://www.rx8club.com/series-i-maj...-turbo-164021/

 

I don't know if you'll get the same benefit with forced induction as the air dynamics are different under positive pressure as opposed to in N/A form where the manifold pressure is near zero or at a vacuum. I'd suggest tuning with it shut, get everything dialed in, then lock it open and do a pull to see if there is a cross-over RPM where it has a benefit. If there is a benefit, set the actuation RPM 200RPM earlier and re-dyno. Otherwise, disabled it permanently.

The SSV and Aux Ports may still offer a tuning benefit depending upon how much RPM is required to spool your turbo; they'd have to be tested like the VDI to determine if more torque could be gained down low. Mazda historically has simplified their induction on forced-induction rotaries, omitting the intake valve setups they use on the N/A motors, but also going with larger 2 ports per rotor instead of the 3 port design of the N/A engines..

 

I'm basically looking at it/operating it like an FC T2 style with no intake valving. I have blocked off the aux ports to simplify the intake for quicker removal. So now for the future I will be going VDI closed as I don't see any benefit for intake flow. It really is some crazy mazda engineering to pull the last few hp out of the NA motor.

I'm not doing a big power build so I'm pretty confident the main ports will be enough. Also way more simple.

 

Yep ... lock the VDI closed . That's what I do .
If you block off the aux ports you will seriously diminish the power capability of a 6 port engine . The primary + secondary ports are way too small to make the engine efficient at high rpm.
Leaving the SSV functional is a good thing as well ... helps with low rpm spoolup and driveability. I actually open mine later than stock .

 

If the secondary injectors are firing and the SSV is closed is that fuel drawn over into the main port?

 

No , it will puddle and run lean if injectors are firing and SSV is closed.<br /><br />around 4300rpm in a turbo ....

 

It's a shame about the spoolup but I'm running a pretty small turbo (t04e) so I'm just gonna stick with always open for now. My secondaries fire based on primary duty cycle so defining that rpm point might be difficult as that's also load based. I find the driveability with the turbo spooling seems to negate the torque issues I had with an open SSV n/a. To some extent anyway.

That said I'm still on the base fuel map with only some basic cruise tuning. It's pretty bush league so I don't want to speak to much to the finer characteristics yet. Got it booked on the dyno on the 25th.

 

What ECU are you tuning with ?

 

Haltech elite 1500, you can setup in the fuel settings you can set max duty for the primaries and minimum on duty for the secondaries. The haltech then uses its volumetric efficiency calculation to determine how much fuel total to inject. The fuel map is in VE values, the ecu figures when to fire the secondaries based on need/load.

Fuel wise I'm running stock yellows for primaries. Secondaries are decapped Subaru injectors that should be about 1100cc at 58 psi. I modified the mounts of my secondary rail to take the shorter length injectors.