Volumetric Efficiency and VVIS Elimination

[M-P]

I am trying to choose a turbo for my car, but am running into one issue while trying to find mass air flows. I have found this chart showing the NSX's volumetric efficiency through the entire RPM range (pretty impressive if accurate).

However, I am assuming this is with VVIS installed. Since I am going turbo, I was planning on eliminating the VVIS system and am not sure how to change the volumetric efficiencies with VVIS removed. Would it change at all at the top end (VVIS completely open?) and only change in the bottom/middle end? Or is the VVIS much more complicated than that?

Any input is appreciated...but please no "just get X turbo...you'll be fine"

Thanks.

 

[Mac Attack]

You can get an idea from this plot on a N/A application:

From about 3250 RPM to about 4750 RPM (a 1500 RPM window), it looks like VVIS added ~10 ft-lbs, or about 5.5% increase in torque.

That's a cool plot - one I'd never seen before. After seeing it, I don't think it considers VVIS. Comparing these two figures leads me to believe that the Honda engineers specifically targeted this RPM range in which to implement the VVIS sytem after choosing cam profiles and crossover RPM to "make the curve more linear."

I'd like to hear greenberet's viewpoint on this too!

Of course, I think a disclaimer should be on the plot above that (I think) the OEM ECU was used for these runs. It doesn't show the timing and AFR's. That can cause a slight difference too as the car is probably running slightly richer in that RPM range with the VVIS disabled and also causing a slight loss of power.


Wow - VE and mass airflows... Are you using a turbo sizing calculator like BW's Matchbot? If so, I'd use the VE's from the VE plot above as they are, assuming you'll completely delete the VVIS assembly.

Dave

 

[M-P]

Thanks...that plot is interesting. It partially confirms my assumption that the VVIS does little to nothing at upper rpms and is mainly used to level out the torque curve when vtec isn't used. I do wish there was one plot with VVIS eliminated and stock ports, but you can't have everything I guess.

Wow - VE and mass airflows... Are you using a turbo sizing calculator like BW's Matchbot? If so, I'd use the VE's from the VE plot above as they are, assuming you'll completely delete the VVIS assembly.

I am using a couple of methods...BW's Matchbot is one of them...the other is making good old fashion excel plots and manually comparing them to compressor maps.

Right now I have my eye on a few turbos in particular (couple of garrett turbos and couple of borgwarner turbos), but it's harder to compare compressor maps when you are looking at pressure ratios below 2.00 which is why I'm so interested in making sure mass flow is as accurate as possible.

 

[M-P]

I decided to just choose my turbo a bit conservatively because those VE numbers are probably pretty optimistic. I'm just going to take that chart and knock 5% off each value I take each 1000rpm. So for use in something like borgwarners matchbot program...

RPM VE %
3000 90
4000 93
5000 95
6000 102
7000 107
8000 103