About Subaru Engines:
Subaru engines come in a wide range of capacities from about 1.1 to 3.3 litres. Ignoring the very small (inline 3 cylinder) versions, they are all of the horizontally opposed flat 4 or 6 cylinder configuration, water cooled, and of all aluminium construction. All of the capacities of flat fours are of similar dimensions to the VW flat fours. The more modern 3.0 litre sixes are also of a very compact design, much smaller than the previous 2.7 and 3.3’s, and Porsche flat sixes. In fact they are only slightly ‘longer’ than the four cylinders, as the belt driven cams drives have been replaced with more compact chain drives. It is possible to fit the three litre six into split screen or bay window busses, Karmann Ghia’s or Type 3’s, and maybe even Beetles. The physically larger 2.7 and 3.3’s are limited the type 25 / Vanagon models (and possibly Karmann Ghia’s?), with their enormous engine bays (it’s very tight though). The 2.7 and 3.3’s are very old designs compared with the later (1990 -->) models though, and have never been sold in the UK.
Subaru engines look very much at home in the engine bay of a VW, unlike most of the other modern engines used in transplants – like they’re meant to be there. However, they are 30 - 50 years ahead of the VW engine in terms of engine technology. If VW had continued the development of the horizontally opposed four cylinder engine, they would probably have come up with something very similar to the modern Subaru units.
Subaru engines from Legacy’s. Impreza’s, Forrester’s, etc. are all suitable for use in VW conversions. In many cases, identical engines are used in multiple models. Differences will be limited to harness routing and ECU mapping, and maybe emissions control equipment,
Subaru horizontally opposed engines:
- really look ‘at home’ in a VW engine bay.
- are available in a huge range of capacities / horsepower ratings, in both four and six cylinder versions.
- are capable of very high mileages when looked after properly. Many don’t consider 130000 mile engines to be too old to use in a conversion.
- are of a modern, all alloy construction.
- are economical in comparison to any VW horizontally opposed engine.
- all have 4 valves per cylinder.
- run very smoothly compared to inline four cylinder engines, as the horizontally opposed design inherently cancels out a lot of the vibration. This especially affects larger capacity four cylinder engines. Most in line 2.5 four cylinder engines have to have balance shafts fitted to control the vibration, making them bulky, expensive, and heavy.
- have five bearing cranks on the 4 cylinder overhead cam designs. This eliminates the crank flexing problems which always limit maximum rpm of the three bearing VW design – even some of the basic model Subaru engines red line at 6500 rpm.
- are modern enough to make a sensible upgrade.
- spin the right way.
- suit all budgets - you can get one for next to nothing, or spend many thousands, depending on what you want.
- are very self contained for a modern engine
- mostly feature a common bellhousing flange design, so one adaptor suits nearly all engine types
- are widely available,
The overhead cam flat fours (1990 ->) are widely available in capacities of 1.6, 1.8, 2.0, 2.2, and 2.5 litres, with all but the two smallest capacities available as naturally aspirated or turbocharged versions, (although not necessarily in all countries). Power outputs range from about 80 to 280 bhp as standard, and 500 bhp engines are available ‘off the shelf’ from tuning specialists (for those with enough money), so there’s one to suit everybody! Some Subaru engines can be very high tech if you go for one of the more recent, higher performance models, with features such as variable valve lift and timing.
The more suitable donor models are all 16 valve, single over head cam (SOHC) and double over head cam (DOHC) designs. They all feature five bearing cranks, and so are not prone crank flexing like VW’s flat fours. This results in a much higher red line rev limit than VW engines. Even the more basic Subaru engines red line at about 6250 rpm – much higher than you’ll get out of a VW engine reliably (without spending many times as much as a typical Subaru engine). They are very high quality, well made engines, and the naturally aspirated ones are surprisingly ‘self contained’ for a modern, water cooled engine (you don’t need an engine compartment with lots of separate bits bolted on everywhere to make them work – most of it is mounted on the engine itself).
One of the biggest advantages of using a Subaru engine is that they are relatively cheap. Low mileage ones complete with all the ancillary parts needed can cost less that an exchange reconditioned VW flat four to buy (although there are also the costs of the conversion parts to be included). The finished conversion should give you 60% to 500% of the power of your original engine, depending on what you want, and will be very much more fuel efficient and drivable than a tuned VW engine of equivalent power. This is mainly due to the modern engine management system, and four valve per cylinder ‘heads.
A Subaru engine is the ideal way to modernise the performance of your VW.