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Old 10-17-2011, 08:14 PM
oab_au oab_au is offline
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Re: Vacuum leak and the IRIS valve

Quote:
Originally Posted by Huskymaniac View Post
From what I have read, the IRIS valve opens at 4000 RPMs. Below this, the two halves of the intake manifold are isolated. If the vacuum line between the pressure regulator and the nipple on the right/passenger side of the intake manifold were to leak, would that cause the air/fuel ratio to be too high on that bank and only on that bank (below 4000 RPMs) and the ECU to adjust fuel trim up to compensate?

What other vacuum lines are connected in a way that could cause an imbalance between the banks when the IRIS is closed?
If the fuel pressure regulator's sensor pipe has a leak in it ,then the fuel pressure will be higher, to all cylinders. The O2 sensors will then reduce the pulse width to reduce the fuel within its available range.

The IRIS opening will have no effect on the vacuum level that they work from.

Quote:
Originally Posted by david_12121 View Post
i don't get this either...how can that valve increase air flow when both the sides are coming from the same intake!
if it acted like a 6 cylinder (6 different timings for 6 cylinders) it would matter but on a double 3 cylinder it won't
. The system has been perfected to utilize the length of the tract from the face of the throttle bodies to the end of the log section that the three tracts run off. This section acts as a Helmholtz chamber that develops an oscillating air pressure wave that is generated by the three cylinders sucking air in turns, one after the other 240* apart.

As the piston in the first cylinder starts from a standstill at the top of the cylinder, accelerates to maximum speed about half way down, to slow to a stop at the bottom. It accelerates the air in the chamber to produce a sine wave of pressure to force the air into the cylinder as the pistol is rising on the compression stroke. The inlet valve is then closed as the pressure is at its max to force more air into the cylinder, virtually supercharging the cylinder. The pressure in the chamber then reduces, but then the next cylinder valve opens to start the air acceleration process again.

This then has the air in the chamber pulsing back and forwards at a rate that is set by the length and volume of the chamber, and the frequency of the inductions. In the EG33 this peaks at about 3000 rpm. If we try to increase the effect by lengthing the chamber, it will reduce the rpm that it maxes at. If we try to increase the engine rpm that it occurs at, we have to reduce the length of the chamber, and that will reduce the mass of air and the developed pressure. If we try to increase the inlet duration by even 10*, it will mean that when the pressure is acting on the first cylinder to force the air in before the valve closes, the next cylinder’s inlet valve will open 10* before it closes, to rob the air pressure from the first cylinder that would fill it. Even the lift and the valve size are chosen to maximize the air velocity at this rpm, which produces the good combustion that it has now at that speed.


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