1991 525I Engine

Just to clarify, you are wanting to put an non vanos engine into a vanos equiped car?

Despite Andyboys lack of tact I think he has a point. The engine itself will probably be a straight swap but fitting the vanos unit onto the non vanos engine is a total no go. On top of this you will, at the very least, need the ecu from the a non vanos car and probably the wiring loom. If the loom isn't compatible with the vanos car then it is going to get very expensive. Either way it probably isn't worth the hassle.

Swapping bits from 1 model year to another model year is rarely that simple in the BMW world due to the associated electronics.

The Vanos unit sits in the cylinder head and is fed by oil pressure from a small electric solenoid valve, also in the cylinder head.

This valve controls the oil pressure to the Vanos, so needs a control unit for it to work properly, hence the extra wiring going into the main engine harness on Vanos models from this valve.

Non-Vanos models won't have either this extra wiring or the Vanos control unit, so I doubt very much it's a straight swap.

Even if you managed to make it physically fit, where are you going to connect the Vanos electrical connections to on a non-Vanos car?

The main engine ECU setting will most likely be different too, as the fuelling and ignition maps for Vanos cars will be necessarily different for non-Vanos models.

At the very least you'll have to swap the ECU, and find out how to wire in the Vanos unit to a non-Vanos car's wiring harness etc.

Andyboy's right I'm afraid-Vanos didn't come out for another couple of years and the cylinder head's completely different, as that's where the Vanos unit lives.

Even if you sourced a Vanos head you'll need the control unit for the Vanos and the associated wiring harness modifications etc. Also, the main ECU will be different to the non-Vanos engines.

So it's no and no I'm afraid