XU9J4/XU10J4 OVERVIEW

XU9J4
The XU9J4 was fitted to early Mi16 and BX16V cars. It’s an alloy block with cast iron liners. The 16V head is an absolute work of art and a fantastic base for building a high output engine. Cars originally fitted with this engine had the Motronic 4.1 ECU (2 row connector). It was designed to run on leaded (or unleaded) fuel, so it did not have a knock sensor, oxygen sensor or catylitic convertor. It was later fitted with a Motronic 1.3 ECU, including a knock sensor. It was commonly known as the 160hp (119kW) engine and designated D6C.

It had many physical similarities to the XU9J2 (and XU5) version as fitted to many Peugeots and Citroens, but many parts are unique. Features unique to the 16V engines include stronger block, ribbed liners, fully counterweighted crankshaft, full floating gudgeon pins, lighter pistons and piston oil sprayers.

XU9J4Z
A derivative of the XU9J4, the XU9J4Z was also fitted to early Mi16 and BX16 cars, in markets requiring strict emissions controls, such as USA and Australia. In addition to compression and cam timing differences, these cars were fitted with the Motronic 1.3 ECU (3 row connector) and had a knock sensor, oxygen sensor and a catylitic convertor. Power output was 108kW (145hp) and was designated DFW.

XU10J4
The XU10J4 was fitted to later model Mi16 and S16 cars. It had an iron block (no liners) and had a cylinder head almost identical to the XU9J4. So may of the tuning tips described later apply to this engine as well. Power output was 116kW (155hp).

XU9J4 / Z Differences

In addition to external sensors and the ECU , there are two main differences between these two engines.

1. Compression

This is achieved by different pistons. Whilst almost identical to the untrained eye, the flat top pistons have different compression heights. They can be identified by either a “Z” or an “X” stamped on the piston crown. The XU9J4Z piston sits a lot further down the bore.

2. Cam Timing

All these engines have the same inlet and exhaust cams. Differences in cam timing are achieved by different cam pulleys. Pulleys are stamped with either a “2”,“3” or a “4”. The #3 pulley is used on the XU9J4Z inlet cam to advance the cam timing 3 degrees (crank). This keeps the dynamic compression of the lower compression engine higher, increasing torque and driveability. Later XU9J4 engines were fitted with #4 pulley on the inlet. This advances the inlet cam by a further 5 degrees to a 106 degree centreline.

The cam timing and lift of these engines are very mild. They feature wide lobe centres to keep overlap low and give a smooth idle.

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