Why did volvo remove the variable intake manifold?

[dikidera]

For a while now I have studied why the P2 platform NA engines had this weird torque dip around 2000-3000rpm. I started to speculate it's either something related to emissions and is related to valve overlap between intake or exhaust(this cannot be cured without a different exhaust) OR it had to do with intake resonance.

Then after googling it became apparent that the 850 20v NA engines had a variable intake manifold, my god, and this eliminated that exact torque dip perhaps confirming it was indeed the problem of intake resonance.




I mean why would they remove this beautiful thing. And also, does the 850 intake manifold fit P2 cars(after 2000)?

[abscate]

Because turbo.....

[dikidera]

I doubt that was the sole reason. The NA engines were produced up to 2007 or even 2009. But the torque dip remained

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But since I am fascinated, I found a cheap VVIS manifold I will explore. Might be useful or it might sit and gather dust. But at $10 it is very cheap.

[abscate]

The P2 platform has VVT which allows some control of manifold flow. My 2005 NA has intake VVT and incredibly flat torque , you can actually start the car in third gear and drive it up to 60 mpg , all in third

[dikidera]

Indeed it does, but the flat spot is still there and at 3k rpm the power comes back. This is not fixed by VVT, at least not measurably so at 2100-3000rpm, but it does help between 1000 and 2000rpm.

I will also try to gather some data.

[454cid]

The P2 platform has VVT which allows some control of manifold flow. My 2005 NA has intake VVT and incredibly flat torque , you can actually start the car in third gear and drive it up to 60 mpg , all in third

Isn't that essentially what the "winter" shift program is, in the 850s?

[abscate]

It is, but my P2 is an M56

[volvolugnut]

My 2001 Mercedes E320 has variable length intake manifold. The system is hidden under a cover between the two cylinder banks. It works quite well to give low end torque. I have read about failure of the switching system resulting in very noticeable loss of power.
volvolugnut

[dikidera]

I kind of want it on my 2.4i, one thing I read is that the VVIS manifold holes are physically larger than the later heads without VVIS. Just the torque difference between 1000 and 3000 rpm is worth investigating how it might fit. I read some articles suggesting one uses something like JB weld to slightly reshape the manifold ports to make them smaller.

Though on the old 850's the torque starts to taper off at 3500rpm, but I guess it's possible to control it over there. Also, I am sure nobody saw it, but the 2.9 NA engine had a huge huge and very cool intake manifold which also provided this very nice torque curve, it normally does not fit 5 cylinders, normally.

[dikidera]

I would like to say that the VVIS manifold intake holes are nearly the same size as the facelift P2 NA head ports. Maybe slightly smaller mostly and maybe just maybe 1mm bigger near the roof where the curves start.

A slight difference can be noted to the right of the manifold in the picture where the ear of the manifold is opposite the gasket. It may need welding of an ear there if there is no bolt hole.

Bore size for throttle body and bolt holes spacing are not yet examined. Vacuum sources are lacking, on the facelift P2 NA manifolds, there are 3 or 4 sources. MAP sensor, brake booster vacuum sources, EVAP and for BIFUEL models, there is a vacuum source for the CNG pressure reducer. On this manifold there are only for brake booster I think.

On the front of the manifold, it lacks the small ear where the dip stick is bolted.

On the left side there is a plug, removable, for the installation of the PCV vacuum hose and PTC preheater. However it lacks bolt holes and I have yet to examine its diameter.

Fuel rail fitment is still unclear, but if P2 fuel rail(with the metal feed pipe not plastic) fits, I would say that it is mostly 90% compatible. Still, it is unclear how much this percentage will drop.

Around the TB area, there is a very large gaping hole, most likely for an IAC valve, which you know does not exist in most facelift models. It can be plugged easily, the problem is of course that around the TB area there would be this small cavity which may or may not affect flow characteristics.
Speaking of flow characteristics, I would imagine that the plenum volume between VVIS and a modern manifold is lower. The facelift manifolds look like they have either longer or much wider intake runners, increasing volume and thus low end torque.
Volume of either manifolds can be measured by plugging all holes and filling with water. So potentially with the VIS manifold it may very well lose some low end torque. Still for $15 and some light porting and modifications, it's worth the test.