[Experiment]

So last night, I was reading the RX-8 repair manual and decided to test how the VDI and the lack of it affects my car. On my canscan logs, nothing changed. I'm beginning to wonder if I even disabled the VDI the correct way. Basically, I went around behind the plastic intake tube and above the oil filter where three solenoids are placed. I disconnected the plug that goes into the VDI solenoid, which is the third (most bottom) plug among the three.

I only got to compare 2nd gear runs between VDI on and off last night. No changes, except that the dip (drop in airflow) at ~7250 rpm disappeared when I disconnected that solenoid plug. The spikes on airflow at the top end is still there whether VDI is on or not. The VDI was designed to supposedly cure those spikes.

[Chart]

I didn't get to log 3rd gear with VDI on except when I did my base dyno run (way before my mods). So, ignore the AFR discrepansies, I used CZ canscan and plain canscan which logs AFR differently.



[What's Next]

Now I got curious. What if I tap a wire to join the solenoid plugs for the SSV and Aux ports. That way, when the SSV opens up and fires the secondary fuel injectors, the aux ports are also open. Would it work that way? Anyone have any experience with playing with these intake ports? I know Jon from PTP did, but he's not replying to my pm.

 

I don't really see any benefit without forced induction. Without the increased airflow the bigger port opening would just decrease intake velocity, I'd think.

 

^ Well, I used to follow that rule when people used to say that tampering with the VFAD would mess up your tuning. Apparently, those theories were only good on paper and mathematical equations. In reality, the dynamics change and the only way to really find out is to test it.

 

well with the vfad "theory" we learned that we didnt understand the purpose correctly. it didnt add any HP. there is no airflow difference between the long length and the short length. the purpose of the long length is to get the same airflow at low rpms as the short length does at higher rpms but be quieter. so the vfad tunes the intake for proper flow at different rpms and for noise level but it doesnt ADD any hp.

it looks like from your chart that leaving it open got rid of the dip at 6250 when the aux ports open. am i reading the chart correctly?

 

anyone have any inputs? So many have viewed this already, yet only one replied? Ask questions or add your 2 cents. I'm just putting this up for people to discuss, since nobody here ever talks about the intake port timing. Honda people didn't leave their VTEC alone, they experimented with it. Our SDAIS is frequently compared to their VTEC.

 

Zoom44, the 6250 rpm is still there for both airflow lines. I didn't touch that yet. The VDI is responsible for the second dip in our dyno charts. If you look at the airflow lines, the fuschia line shows the dip after 7250 rpms, while the maroon one doesn't.

From the manual, it shows that the solenoid gets the signal from the ECU. When the solenoid gets a signal, it switches open something in that vacuum control box so that the VDI actuator opens up. I didn't leave it open. I disconnected the solenoid signal plug so that it remains closed at all times. At least, that's what I think is happening.

In my next quest, I would try to share the SSV solenoid signal to the Aux ports' solenoid so that they would open at the same time. This way, SSV and Aux ports all open up at 3570 rpms and above. Notice how the AFR line suddenly drops after 4000 rpms, while the airflow stays consistent?

 

am i wrong that the "maroon" line goes up to a point from 6k while the fushia basically plateaus?

thanks for the clarification i didnt read the first post closely enough

 

the pcm has a CEL for stuck open for aux ports. im not sure about vdi. perhaps they are all made to fail open and by disconnecting the wire you opened it. hoiw long did you leave it disconnected?

 

^ Uh, I don't get that either. It does go up a little higher than the stock form. I just disregard it since I know I am not changing anything there. The fuschia line was taken before my REVi + Ram Air if that helps. Regardless, the dip at that point is still there and that dip is very prevalent in RX-8 dynos. I wish I had my own dyno machine to play with. I like how the 7K rpm dip is gone, but I can't say if it added any power at all.

BTW, I placed colored vertical lines as highlighters to port changes. Those are points to note that the port area dynamics are suppose to change due to ports opening.

I unplugged it last night and took 2nd gear runs. I took a 3rd gear run this morning and I haven't connected it again. I don't know about that "left open in safemode" because from the manual, you have to apply negative vacuum using a vacuum tool to open the VDI. By default, it is closed.

 

just a thought about the fail open. doesnt sound like it does from what you say. nice to see the revi + ram difference in the airflow

 

I made a 3rd gear run last night. I have recently disconnected the ECU and so all LTFT is zero (yey!). I'm amazed how the AFR doesn't go 11:1 all the way when the LTFT is zeroed out. The run was at the same timeframe, same location, same routine. I did VDI on and VDI off.

Below, the black lines are the stock line (VDI on) while the colored ones are with VDI off:



^^^ look how the 7K rpm dip disappears and the airflow rises higher than with the VDI on. Can anyone explain why this is happening? RG? VDI is suppose to let the engine breath more and better right? Well, the dip just defeats that purpose IMO.

 

VDI is marketed as a resonance feature to increase both torque and HP.
However, resonance schemes are always tied to reduced NVH programs implemented by the bean counters. At least, that has been my experience with Mazda.
The KL motors had VRIS which was supposed to do the same thing, but it mostly just cut intake roar. Most people just blocked their's open.

What the VDI seems to do, IMHO, is disrupt aiflow in a way that is difficult for the PCM to compensate.
I'd like to see runs with it pinned open.

 

^ You've played with the RX-8 ECU, so let me ask you then. To keep the VDI open, do I just ground the wire that goes into the ECU for the VDI solenoid? From the manual, it seems that the VDI solenoid, along with other solenoids, receive constant voltage from a relay. The ECU provides ground to activate the solenoids. The APV, however, is getting voltage from the ECU directly.

 

I wonder what effect it has on a turbo'd car. I think someone here needs to do some dyno runs. I'd pitch in $10 toward that dyno chart to see it.

 

The VDI should probably be wired open.
Just put a ZIP tie across the actuator. I don't think those solenoids are designed to have anything over a 60% duty cycle, so grounding one open will probably burn it up.

Turbo is a whole different story since the resonance effect is completely ruined.
I'm thinking of connecting the APV to the VTEC output on the E-Manage to open it under boost and then just wire the SSV and VDI open.

 

If I read Xyntax's plot correctly VDI open resulted in more torque, less hp.

It's been suggested that for a turbo it's better to keep VDI closed.
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Harmed By Nexium

 

You can do that?! I was thinking of using CZ to control the APV, but I'm not sure which module in Emanage to use to trigger it. If you can do this, then a DIY would be nice. Watch out though, the APV motor has a warning about not supplying voltage for more than 3 seconds because it could burn out the motor. I still can't figure out a way around that.

 

ps. After looking at the initial graph I posted and the one I just did today, it looks like my Aux ports did not open at all. Just look at 6500 rpm. The initial graph has a sudden jump up to 200+ gm/sec. My latest graph didn't have that at all.

PUR NRG, how could you tell TQ and HP from the graphs I posted? All I have is airflow, ignition and AFR. Also, isn't TQ directly related to HP via RPM?

 

A DIY would be possible, though it would require a dongle like the one supplied in the Greddy turbo kit.
Basically, it is an electronic switch that is turned on or off at pre-selected load points based on boost and RPM. In the Greddy kit (and my system) it spoofs the temp sensor circuit down to 140°F or so to put the motor in open-loop. The same type of circuit could just tie the solenoid to ground and be controlled by the same MAP.
The EMU could do more than one of these if required.

 

I was looking at the orange line; I'm used to seeing two lines (hp and torque) in graphs and didn't stop to think about the shape of the line itself. Nevermind.
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Marijuana strains

 

That is interesting that with VDI open the line stayed higher. Can't quite figure that one out unless maybe someone messed up when designing it. It's weird though that there is no difference anywhere else lower in the range. Typically when something is tuned it also has effects at the harmonics of the tuning point. On the RX-7's that had VDI it was noticable when it opened and you did lose low end when it was open full time. You'll have to play with this some more.

The VDI is nothing more than a vacuum actuator. You can just zip tie it open. The mechanical part comes into play as there is a little electric valve that opens or closes to allow air to this solenoid. Don't worry about it. Just wire open the valve.

 

RG, the VDI was left closed not open, which made the line stay high and not make a dip. Well, that's how I think happened when I disconnected that VDI solenoid wire plug. I'll probably have time to tie open the actuator this Thursday night. Thanks for the tips! I'll make sure I log it.

I'm still concerned about my Aux ports now. The graph didn't have that 6.5K rpm jump anymore. Any way I could test whether my Aux ports are really opening or not? Problem is that it's motorized and I've tried looking for that motor from the diagram. It seems like it's tucked away beneath the alternator area.

 

I meant to say closed not open. You should still try a run each way for a comparison.

The motor for the auxiliary ports is located on the lower manifold. You can see it from the passenger side of the car. It doesn't mean you can necessarily get your hands in there easily but that's where it is.

 

If these results are repeatable, then it's kind of depressing that the other ports are so ineffectively tuned.

But it kind of gets me thinking. I may be talking out of my *** here, but bear with me for a second.

It appears that the ports have nothing to do with tuning N/A airflow, because when opened they seem to produce little effect on total airflow, except some negatively affecting eddy currents at high rpms, quite feasable. But this does seem to say that this engine was built for FI, because while the ports may have a negative effect on N/A flow, a pressurized system could make very effective use out of the extra ports as a more efficient way to deliver available PSI.

Kind of reminds me of Hymee's SC dynos, loss of air velocity at the top end.

 

I wouldnt do it... leave it the way that it is, and be happy with it, that is, if you like your warranty.... either way... customer pay is way better than warranty work :P