Subaru WRC Inlet manifold

[boyracer]

Hi all, been a while.
I've got a McKlien calendar sitting on my desk at work, current view is of the Subaru WRC engine from Japan 2006, though I think it's been carried forward to the latest model. After the intercooler there is an increase in the manifold pipe diameter for a short section before stepping back down to the same size as the rest of the system and going into the throttle body. A friend suggested that it was for dropping the air temp, though I don't see how. Every way I look at it from the gas laws I contradict myself. I think it's gotta be for reversion in the inlet as the changes in diameter are not blended so they must be causing all sorts of flow issues, though it obviously works for them ?

Any ideas ?

[GORDON STREETER]

Its difficult to actually see from a photo and and unless you could be hands on it could be anything . Also you don't know if the internal diameter is different. Is it possible there are any sensors in it that you can't see from the picture ?

[1200Datto27]

You would most likely find that there are properly radiused bellmouths inside the pipework to make the flow paths better. I remember reading somewhere that the Prodrive went back to the rearward facing throttle body as they found that there was not enough volume in the pipework with the forward facing unit. This meant that when the drivers opened the throttle the engines had a little hiccup as they couldn't breathe enough (It is difficult to increase the volume of the plenum on a EJ20) air. I would say that the bulged pipework is to add mor volume into the system for that reason as well.

[zac510]

That is correct, I have asked an engineer about it.
It is also probably in the regs that they're not allowed to modify the manifold.

[Notso Swift]

Yes they "pack" the air so when the throttle opened there is a mini boost spike, also helps with keeping the turbo spooled, the wall/pulse of air gives the turbine a little kick. They peak at over 30 psi with a 9.5:1 compression. You can't go too far as too big a volume makes the response doughy as the pressure drops back and the void has not been filled by the next lot of air.
I supose the other way to look at it is since the restrictor will only flow a fixed volume of air you may as well keep as much air moving though the hole even though the throttle is closed