Boost and VVIS

[the nsxnut]

Next Topic:

Is the Variable Volume Intake System function controlled electrically, via ECU actuated solenoids alone, or is there a necessity for vacuum to be present for it to function properly?

The relevance here is that, under NA conditions, at a certain rpm, with a certain level of vacuum present, the VVIS butterflies open up. So, if one is using FI, and boost (positive pressure inside the intake manifold) is present, would that then inhibit the function, if it relies on vacuum to operate? If yes, then, are we all running around under boost without the benefit of the VVIS, because it needs vac to function? If so, how can that be bypassed?

It is rumoured that the 'legendary' RTR NSX w/the custom Vortech setup had fully disabled the VVIS, so that the manifold had max volume fulltime.

OK, team, have at it...

 

[Lud]

VVIS is operated by manifold vacuum.

Almost a year ago I suggested one of you BBSC guys remove it and see what happens... http://www.nsxprime.com/forums/showthread.php?s=&postid=28141#post28141 I think it will improve things on any forced induction car* -- the more boost the more improvement.

VVIS is already removed when you install a CTSC since the whole manifold is replaced, otherwise I would have tried it already.

* Disclaimer: This is just my whacky theory and I'm not a mechanic or a tuner or an engineer.

 

[Larry Bastanza]

After a little looking in the service manaul, the VVIS uses vacuum as a "power source" to open the butterflies, and the ECU controls when the butterflies open. It shows it in the 1991 manual on page 11-119.

It states this provides higher torque during lower RPM operation. I think it is actually a pretty common system used in many performance engines. From discussions with Andrew at RealTime it does a good job, but when you are trying to get as much HP as possible you can sacrifice some rev range. The butterflies are an overall obstruction, so taking them out will give you more HP.

This was typical of the orignial Porsche "slider butterflies" used in their Can-Am cars that worked more like the shutter of a camera in that when they were open, they were gone, so the intake had a clear path.

Funny though, since in the case of SC's, especially centrifugal, non overdriven setups, it would seem intuitive you would want the lower torque. If you can accomplish the lower range torque by overdriving and blowing it off, then I would think taking them out may be worthwhile.

Just my $.01 Still trying to feel my way through this FI stuff.

LarryB

 

[NA1 #2853]

isnt there supposed to be a vacuum resevior with a checkvalve to provide operation to the bufferflys when vacuum isnt present in the manifold?

cause at WOT on a N/A car there is very little vacuum.

-Ray

 

[Larry Bastanza]

Ray,

If you take a look at the page I mention in the on-line service manual you will see there is.

LarryB

 

[the nsxnut]

AMAZING RESULTS

At a dyno tuning session today, I decided to get to the bottom of this. After studying the VVIS mechanism and the manual (before going to the dyno shop), it was understood how to test and disable the VVIS. I have a comrade who assists me with NSX service and tuning my BBSC (KODIAC on Prime). We learned that the vac line #3 provides the vac which operates the system, as noted above. This is one of the throttle body hard lines that turns rearward, and then goes straight down vertically next the the TCS assembly. A rubber hose joins it to the VVIS control solenoid. One can simply pull off the hose, and cap the hard line, to disconnect it. When disconnected, the VVIS butterflies are left in the OPEN postion.

We first wanted to know if the VVIS system is functioning under boost. It does not. With the vac connected (OE config), the butterflies remain in the CLOSED position throughout the rev range. Evidently, the postive pressure inhibits its function. Disconnected the vac line, now the butterflies are open, and HP increased 10% at peak output. I'm dead serious. This was done on back-to-back pulls, where the only variable changed was plugging in and unplugging this #3 vac line, causing the VVIS butterflies to remain open full time. This test also verified the VVIS function, because we see a gain in TQ below 4K rpm with the butterlies closed, but that is more than offset by the significant increase in peak HP at 8K rpm with the butterflies open. Take note, that the butterflies FOR SURE do not open under boost (at least on my car, which had in place it's complete OE VVIS, untampered with; that is, until today!). This data was verified by repeating the test on back-to-back pulls later in the session as well, after some AFR/timing adjustments were made, and we still found a 10% diff in peak HP with the vac line on/off.

I would certainly suggest anybody with FI of any type look into how your application may be affected.

I will also mention that the AFR is richer with the butterflies closed. We did all of our tuning with butterflies open, as my primary use is on the track, top 50% of the rev range, where the VVIS butterflies must be open for optimum output.

I can't emphasize enough that this is lab tested and proven, not couch conjecture.

Good Luck.

 

[Sig]

That is a tremendous contribution to FI community! I am amazed this did not get any publicity earlier. So, it sounds like you realized between 30 and 40 more rwhp. That is quite a jump.

 

[MiamieNeSeX]

After a little looking in the service manaul, the VVIS uses vacuum as a "power source" to open the butterflies, and the ECU controls when the butterflies open. It shows it in the 1991 manual on page 11-119.

It states this provides higher torque during lower RPM operation. I think it is actually a pretty common system used in many performance engines. From discussions with Andrew at RealTime it does a good job, but when you are trying to get as much HP as possible you can sacrifice some rev range. The butterflies are an overall obstruction, so taking them out will give you more HP.

This was typical of the orignial Porsche "slider butterflies" used in their Can-Am cars that worked more like the shutter of a camera in that when they were open, they were gone, so the intake had a clear path.

Funny though, since in the case of SC's, especially centrifugal, non overdriven setups, it would seem intuitive you would want the lower torque. If you can accomplish the lower range torque by overdriving and blowing it off, then I would think taking them out may be worthwhile.

Just my $.01 Still trying to feel my way through this FI stuff.

LarryB

Great job! 10% is a considrable amout of hidden HP. Is disabling the the butterfly enough or would removing it be a better fix? How much did you a/f differ after the change? Any noticable difference in lower RPM torque and throttle response?

Thanks Mark
Armando

 

[nsxlover]

This is a great post. I am going to try this on my car. Just cap off the line and that is it? Will it work the same way on turbo cars?

Rob

 

[sjs]

Well done!!!! I too am amazed that the developers of the various SC and turbo systems have not tested the VVIS under boost. Of course CT is excluded since their system eliminates it completely, but what of the others? I'll need to check my Bell TT since it's been a few years since I did the install, but I don't think anything was done with that vacuum line.

Of course, most of us spend more time at 4k than 8k so it would be nice to see complete power curves with and without the system active. For a BBSC which is a bit short on low-end grunt the best solution might be a hobs switch and valve to flip that line from vacuum to "open" as you pass though atmospheric towards boost.

 

[Lud]

Cool! I think there is more waiting if you remove the entire VVIS butterfly valve setup completely. Just speculation. Of course you lose the option of using a switch to open/close it as pressure changes, but I have a sneaking suspicion that it doesn't make a dramatic difference for low end power anyway, I think it may be mostly an emissions gimmick. Again more speculation.

Mark I'd like to see the dyno graph with it forced open. I'm guessing my <a href="http://www.nsxprime.com/forums/showthread.php?s=&postid=28141#post28141">previous theory</a> that over-riding VVIS would get rid of the "bump" around 5000RPM typical of many BBSC dynos graphs was wrong if you found it VVIS not being activated at all under boost? Oh well -- at least there was indeed a real difference in power!

 

[len3.8]

Lud, if comptech basically removed the VVIS, what did they put in to replicate its function? If anything was put in to replicate it, would CTSC cars benifit from removing comptechs replacement?
((Did that make sense?)) If it is an emmissions gimmick, would it cause a fail?

((Really trying to find my way within the FI scene))
Len

 

[Lud]

Lud, if comptech basically removed the VVIS, what did they put in to replicate its function?

Comptech's SC manifold completely eliminates anything VVIS-like. They did not attempt to replicate the function of the OEM VVIS setup.

 

[RacerX-21]

Comptech's SC manifold completely eliminates anything VVIS-like. They did not attempt to replicate the function of the OEM VVIS setup.

All you will need is shorter screws.

 

[KGP]

Re: AMAZING RESULTS

We first wanted to know if the VVIS system is functioning under boost. It does not. With the vac connected (OE config), the butterflies remain in the CLOSED position throughout the rev range. Evidently, the postive pressure inhibits its function. Disconnected the vac line, now the butterflies are open, and HP increased 10% at peak output.

Very nice contribution, Mark. I recall Lud's post from quite some time ago, and I'm suprised nobody else has tested before now and posted results. I'm also suprised that MB did not consider this. 10% is quite a lot. It will be interesting to hear results from others, as I suspect there will be a few more following suit. Hopefully 10% is the norm.

 

[the nsxnut]

Updates...

I'll be glad to answer as many ?'s as practical.

First, let me share credit with my local buddy Rob (RacerX-21). I've been thinking about this issue for a while, and, of course, Lud brought it up some time ago too. But, it was after a conversation with Rob, who is building another full race motor, that I found the means to conclusively test this. Thanks, Rob.

Is disabling the the butterfly enough or would removing it be a better fix? How much did you a/f differ after the change? Any noticable difference in lower RPM torque and throttle response?

Ultimately, if you want to permanently abandon VVIS, it would be ideal to fully remove it, as it is taking up space in the flow path of the intake. On my motor, using latest SSBB, the AFR was about .5 point richer with the butterflies closed. With them left open, I've tuned to a very reliable 11.5-12.1 range. With them closed, and no change in tuning, I saw 10's & 11's. Like all big changes we make, there is a compomise. Here, it is giving up low-end torque, which the VVIS was originally designed to enhance. From about 3500 rpm to 4500, the diff was about 20 ft-lbs until the curves cross at about 5K, and then it takes off and there's no looking back. Peak TQ comes at 7K, and is also 10% higher than with the butterflies closed. The diff in HP below 5K is insignificant, the curves almost overlay, with a few more ponies available with the butterflies closed below 5K.

I regret that I lack a scanner or dig camera and cannot post the plots.

 

[Larry Bastanza]

Mark,

Very cool stuff.

sjs,

For a BBSC which is a bit short on low-end grunt the best solution might be a hobs switch and valve to flip that line from vacuum to "open" as you pass though atmospheric towards boost.

With this idea the butterflies would open when the vacuum line is "open"?? You lost me. (Probably because I do not understand what a "hobs" switch is)

Thanks,
LarryB

 

[KGP]

Re: AMAZING RESULTS

I would certainly suggest anybody with FI of any type look into how your application may be affected.

I will also mention that the AFR is richer with the butterflies closed.

Might be wise for the BBSCr's to check their current fuel pump flow (assuming OEM) before messing with this.

 

[the nsxnut]

Yes, if you have a *marginal* AFR (12.6+) on an OE pump, and then make this change, if it is effective on your motor, then AFR will probably go into the 13's right away...

 

[sjs]

I think it's probably "Hobbs", but it is a simple on/off switch triggered by pressure/vacuum. (then again, I may have the wrong term entirely). In any case, I was thinking that the switch would in turn operate a solenoid valve. Under vacuum the valve would leave the pluming stock (routed to the VVIS), then at the switch point (atmospheric pressure) it would be switched to the equivalent of what nsxnut has suggested.

Frankly I'm not sure I understand how it doesn't "work" as-s since it sounds like the lack of vacuum at WOT is what signals it to switch already and boost is just an extension of no vacuum. But there must be more to it so I figure it might work to mechanically switch the vacuum line under the appropriate conditions. Just "thinking out loud", but it seems to make sense. Of course, BZ can probably come up with a cool electronic solution. Perhaps the AEM can be programmed to control this.

 

[Larry Bastanza]

I think the vacuum really is the power source to open the butterflies. The ECU controls a selonoid to open the vacuum line to get the butterflies to open. There is also a vacumm reservoir w/check valve to keep the vacuum source when WOT occurs.

Thanks,
LarryB

 

[Factor X Motorsports]

Well done!!!! I too am amazed that the developers of the various SC and turbo systems have not tested the VVIS under boost. Of course CT is excluded since their system eliminates it completely, but what of the others? I'll need to check my Bell TT since it's been a few years since I did the install, but I don't think anything was done with that vacuum line.

Of course, most of us spend more time at 4k than 8k so it would be nice to see complete power curves with and without the system active. For a BBSC which is a bit short on low-end grunt the best solution might be a hobs switch and valve to flip that line from vacuum to "open" as you pass though atmospheric towards boost.

Sjs,

We actually remove the butterflies completely on our FI motor builds. This was brought to our attention about a year ago by former forum member NSXTC. The results have been fantastic. In regards to your Bell TT. We just finished building a motor for Speed Demon, the motor build included the butterflies being removed. On just a little over 5psi she put down close to 400rwhp on the Dynapacks. This is much higher than the previous Bell’s we have had on the dyno. For those interested we have a new Phenolic spacer being made. Once tests are complete we will post the results.

 

[ncdogdoc]

You want longer runners to improve low rpm power, and shorter to improve high rpm breathing. The VVIS gives both, with the low setting created by the valves being closed creating a long runner setup, improving low end torque and drivability. When they swing open, then the air has a straight(er) shot to the intake valve without any "velocity" tuning to help manage the airflow at low cfm's.

I think a simple electric switch tied to rpm would be better than trying to mess with vacuum in FI. You could use any rpm monitor such as Bryan Z's chip to create a voltage at a certain rpm, triggering a relay and solenoid or motor to swing the plates. In the long run, it is probably not necessary with large cfm FI setups as even at lower rpm there is enough air pushing through that "tuning" the airflow for proper atomiztion and swirl with a longer runner may just be a moot point. Then again what do I know, I run NA

 

[RacerX-21]

You want longer runners to improve low rpm power, and shorter to improve high rpm breathing. The VVIS gives both, with the low setting created by the valves being closed creating a long runner setup, improving low end torque and drivability. When they swing open, then the air has a straight(er) shot to the intake valve without any "velocity" tuning to help manage the airflow at low cfm's.

I think a simple electric switch tied to rpm would be better than trying to mess with vacuum in FI. You could use any rpm monitor such as Bryan Z's chip to create a voltage at a certain rpm, triggering a relay and solenoid or motor to swing the plates. In the long run, it is probably not necessary with large cfm FI setups as even at lower rpm there is enough air pushing through that "tuning" the airflow for proper atomiztion and swirl with a longer runner may just be a moot point. Then again what do I know, I run NA

Your theory is correct, but these butterflies were designed for a stock engine and may limit flow numbers for modified engines. Testing is always the best way to know for sure. The ultimate would be to have variable length runners, but they may need to be a different size. The spacer is also a good thing to try. My guess is that for some a different intake would be warranted…

I think that Mark said that he lost a small amount of low end power by not using the system, but the overall hp warranted leaning towards the high RPM range. I think he will find that eliminating the system, he will improve everywhere.

I think Mark failed to mention his peak HP and TQ results… Whats that all about?

 

[BryanZublin]

I can't offer much more than has already been stated, other than to add this comment: The Mk1 Toyota MR2 added a supercharger in 1987. At that time, they eliminated their version of VVIS for the SC model because of (presumably) no performance benefit. The SC was positive displacement type (boost available at low RPM).