IceY2K1

iTrader: (3)

Can someone please explain what changes to cause this?

I understand that there are different length intake runners and that the air flow changes from long to short(or short to long) at 5200(or 5600?)rpms. Cam position? VVT? If so, what causes them to change and is it something WE could play with like the VTEC controllers do to change at a certain time?

I'm just not sure if something mechanically or electrically controls this or some physics of fluids is behind it.


Thanks!

SteVTEC

My understanding is that on the 00-01's the valve timing is static (non-variable), as is the cam phasing (non-variable). The variable intake manifold opens up a second shorter-path set of runners at 5000rpm. You probably wouldn't want to play around with this x-over point as it's pre-optimized by Nissan. I'm not even sure how it's optimized, but no, a VTEC controller wouldn't help you.

I believe the 02's have variable cam phasing and it's continuously variable. The 02's also have the variable intake manifold but I forget where the x-over point is. I think it's 3600rpm or something around there. I forget.

UMD_MaxSE

iTrader: (1)

i think that intake manifold runner switch is vacuum controlled

madmax2k

I believe that the runner switchover is accomplished by using engine vacuum as the motivational force, but the ECU actually tells the solenoid when to apply vacuum to the flapper, thus making the changeover. It seems to always occur at precisely 5000 rpm when at WOT.

2K2DEMAX

iTrader: (1)

From the Maxima ESM........

When the engine is running at low or medium speed, the power
valve is fully closed. Under this condition, the effective suction port length is equivalent to the total length of the intake manifold collector’s suction port including the intake valve. This long suction port provides increased air intake which results in improved suction efficiency and higher torque generation.
The surge tank and one-way valve are provided. When engine is
running at high speed, the ECM sends the signal to the VIAS control
solenoid valve. This signal introduces the intake manifold
vacuum into the power valve actuator and therefore opens the
power valve to two suction passages together in the collector.
Under this condition, the effective port length is equivalent to the
length of the suction port provided independently for each cylinder.
This shortened port length results in enhanced engine output with
reduced suction resistance under high speeds.

So it's

ECM signal at 5k RPMs->solenoid valve->power valve actuator->power valve ->which opens the port to the shorter runners. As Steve said, I wouldn't try to tamper with this as it seems that Nissan did indeed optimize it.

Peace....

Keven97SE

The 5100 rpm switchover point is already optimized. It "kicks in" right when the engine needs it...right when the torque starts dropping off. You wouldn't even want to bother with changing that point.

The intake manifold works by opening an internal valve inside the plenum at 5100 rpm. The valve increases the effective plenum volume. The intake runners do not change (no second set of runners). The larger plenum volume increases the resonance frequency of the intake charge to optimize cylinder filling at higher rpms. Intake resonance can provide a supercharging effect when the engine is operating within a certain (narrow) rpm range. With just the low-rpm setup (similar to the 4th gens), the engine is optimized only at low- to mid-range rpms. The 4th gen torque is choked off past 5000 rpms because of this. By switching the resonance frequency, the 5th gen intake manifold "gives life" to the engine past 5000, decreasing the torque falloff and greatly increasing HP.

IceY2K1

iTrader: (3)

Thanks for the info guys. Let me ponder/absorb some of this.

I don't think it would be beneficial to change the switchover point on a STOCK N/A Maxima, but what about if you run a SC, turbo, or NOS?

I'm wondering if the switchover occured sooner(i.e. <5000rpms) and you provided MORE Air/Fuel, if you could get more useable area under the "Power Curve" by causing the hp curve to intersect with the tq curve earlier.

Nissan engineers optimized the intake/intake manifold/ECU/exhaust system for STOCK engines, while under MANY constraints about noise, fuel efficiency, smoothness, reliability, etc..

I know it's theoretical, but I'm just wondering if you can enhance what Nissan already designed into the engine to have a synergy between increasing air flow with aftermarket parts.

Again, THANKS!

Keven97SE

If you add supercharging or turbocharging, then yes there may be some very slight benefit in changing the intake manifold swithover point. HOWEVER, it's not that the high-rpm setting on the manifold just "flows more air". That is not at all correct. It flows more air at 5500 rpm vs the low-rpm setup (non-activated). If you were to use the high-rpm setting (activated) at 4000 rpm, you would almost certainly flow less air than with the low-rpm setting.

Whether or not the high-rpm setting flows more air is completely rpm-dependent.

But, since I don't think I'm getting my point across re: functionality of the manifold, there is no gain in tweaking the switchover point on a n/a car, and I doubt very very much that there is any gain on a SC/TC car also.