Is the BMW M50B25 a 1JZ we didn't know about?
It shouldn't come as a surprise that prices of our hero cars from the 1990s have sky-rocketed as the era of Hypercolor, rap-rock, and CD-ROMs was more than two whole decades past. This has meant prices for some of our favourite engines has also risen sharply, making engine swaps a spicier burrito to unwrap today.
Years ago it seemed we Australians were swimming in an unending supply of Japanese performance motors, ready and stocked at import yards as complete engine packages or full front-cuts, which we could verily yeet into all manner of many and varied nuggets. But today those $1000 (Aus) engines are now five times that price (or more), are often difficult to find, and most will need an expensive rebuild before pumping out the kinds of hosepower we are used to.
So this brings us to engines we previously walked past while there were cheaper, easier options at hand - like BMW's M50, and specifically the M50B25. Some JDM snobs will turn their noses up at the thought of a European engine, but these are cheaper than many people realise, and with modern fuels (E85 enters the chat), turbochargers and engine management systems (g'day Haltech!) these engines could be a great option for engine swappers wanting to do something different from an LS or Honda K-series.
So what's the deal with the M50? It is an in-line six-cylinder offered in a variety of capacities, from 2.0-litres, up to 2.5-litres, and it was a significant upgrade over the previous M20 six.
The M20B25 it replaced, most commonly found in E30s, is a near-ancient 125kW SOHC 12-valve engine that uses a timing belt which needs to be replaced every 50k kilometres (when driven enthusiastically) and requires regular valve adjustments. When the M50 came along in 1990 it did away with all of that old nonsense in favour of a beaut alloy twin-cam, 24-valve cylinder head, coil-on-plug ignition (fairly advanced for 1990), and a plastic intake manifold.
Getting down to the nitty-gritty, the M50B25 spans a 2494cc capacity, with an 84mm bore and 75mm stroke, a 10:1 compression ratio (10.5 in the TU), and around 141kW (189hp) in stock, aspirated form. While later M52 and M54 sibling engines used aluminium blocks, the M50 rocks tried-and-true iron, and this with the 10.5 comp ratio means (with a good ECU, ARP head studs and E85) people have made up to 600rwhp with stock rods and pistons.
In 1993 BMW introduced the world to VANOS and this meant the M50B25TU (Technical Update) replaced the original, simpler M50. VANOS is BMW's variable engine timing system and the 93-on M50s featured it on the intake camshaft with two positions - the valves open later at low-RPM for smoother running, and switch to opening earlier at high-RPM for improved performance.
M50s were found in the E36 3-series and E34 5-series cars, with the 3-series running a rear-hump sump and the 5er running a front-hump (making it perfect for E30 swaps). These engines have been incredibly popular swaps into E30s for nearly 20 years now, and there are plenty of outlets selling boost-friendly pistons, con rods, cams, intake and exhaust manifolds for punters wanting to slap a stout six-banger in their project.
The all-aluminium, OBD2 M52-series replaced the M50 in 1996, and featured a new 2.8-litre top-spec variant for non-M cars. In 1998 the M52 was again treated to a comprehensive mid-cycle refresh as BMW brought out the M52TU featuring dual-VANOS.
There is a wealth of information on the Internet regarding these M5x motors as people have been playing with them since they first came out, and there is an epic aftermarket to support them, too. Did I mention these twin-cam BMW sixes sound great?
We see a lot of people complaining online about wanting to see something new. So, before you give up on a project because you can't afford $7k for a complete 1JZ, maybe have a look around at other engine options.