IRIS valve : not too techical Q

[jsteele22]

This one shouldn't be too hard.

I'm wondering what it's like when the IRIS valve opens/closes. Can you feel a distinct change in engine behavior (power/toque, sound) ?

Also, does the valve "snap" open/shut pretty quickly, or is it a slow transition ?

[NikFu S.]

There is a distinct difference in the sound.

Lets say you are cruising in third, you push down on the throttle a bit, and you don't really accellerate quickly. The rpms rise a touch and the sound moans a little more. IRIS is closed. It's an rpm dependant system.
Push down harder, likely the auto tranny will downshift. You geet the "BWAA" sound associated with higher rpms but I think if the valve remained closed at higher rpms not only would you be going slow but it would make more of a "BVVV" or "BWOO" note.

I think the speed of the valve can vary. Under hard accelleration it is pretty quick, but driving normally you should be able to hear the note change at around 3000-3500rpm and it's more leisurely.

This is all speculation though as I have no techincal knowledge of the IRIS.

[Trevor]

Originally Posted by jsteele22

This one shouldn't be too hard.

I'm wondering what it's like when the IRIS valve opens/closes. Can you feel a distinct change in engine behavior (power/toque, sound) ?

Also, does the valve "snap" open/shut pretty quickly, or is it a slow transition ?

The valve is actuated via a solenoid valve controlled by the ECU. This valve opens or closes so as to control intake manifold pressure, subsequently applied to a diaphragm within the Induction Control Valve (Iris valve). Manifold pressure/depression is therefore the actual final motive force which moves the valve.

As I understand it, there is no progressive action and the valve is either open or closed. However as manifold pressure is involved this is open to conjecture.

I very much doubt that it is possible to notice any audible difference, given the location and nature of the inlet system.

[jsteele22]

Okay, thanks for the replies. I am really looking forward to driving this car (eventually ).

The main reason I asked about the IRIS was that I'm going to use an aftermarket ECU, and was concerned about how it might make tuning more difficult. At one particular point in the RPM/MAP table (around 4000 RPM, say) it seems like there are 2 different values of volumetric efficiency (IRIS open, IRIS closed). If the valve snaps open pretty quickly, then it's probably okay to ignore the issue and assume that over 4000 RPM the IRIS valve is always open. Anyway, this is probably a minor issue compared to all the other stuff I still have to deal with.

[Trevor]

By and large I would say that your thinking is in line.