I am wondering whether my wonderful 1.8 dohc lump has any variable timing on it, just for interest. I'm in the opinion that it might, because at about 4.5-5k revs, it lets off this wonderful high-pitched whine, which changes to an insane whine at 6/7k revs. It might just be the noise the engine makes, but i'm interested to know exactly what it's doing under there...certainly other cars i've been sat in that have variable timing systems (vtec, variocam etc) do start whining too.....

No variable valve system but I'm pretty sure the 1.8 has VICS (Variable Inertia Control System). This changes the length of the intake manifold.

How does it change the length of it? Surely its a fixed piece of metal to each cylinder's intake?

Does the V6 have VICS too Robbie...?

Don't you just love acronyms? The Japs certainly do....

I've a feeling the BGs had the VICS system, but as far as I can see, there's no way the BA's intake length can be changed dynamically. The early 1.8 BA's have a small resonator box between the airbox and throttle body.

Mark

Yep, 1.8 DOHC engines from the BG's have VICS - havent driven one without it so ive no idea what it does

It works by a series of shutter valves (look like throttle valves) in the intake manifold. They just direct the air along a different route. It is similar to the dynamic chamber thing Mark mentioned. The V6 has this also. A lot of Mazdas used the VICS system, the high power RX-8 has about 3 different intake manifold "tracks" depending on engine speed and the number of injectors it's firing.

edited to say... It's actually called VIRS on the V6, don't know what that stands for though Variable Intake Routing System maybe?

I guess these are ECU controlled are they?


Mark

Yep, the acutator valve looks like a distributor vaccum advance unit fixed to the inlet manifold. Follow the pipe and it should lead to a control valve with a 2 pin connector on it and another rubber pipe. The control valve is open & shut by the PCM as required.

That all sounds really cool....guess its the different air paths that make the whistle/whine.

The different air paths tune the intake tract to deliver greater than 100% intake volume at more than one rpm band.


Mark