….or a history of VW engine conversions, and why Subaru engines are most commonly used:

From when they were new, rear engined VW’s were always quite widely tuned, with all sorts of carburetor swaps, capacity increases, sportier cams and supercharger kits, etc available. Until the 1980’s or 1990’s, the objective was always to increase the power output – the engines were economical enough relative to everything else at the time. The VW flat 4’s – especially the air cooled models are very tunable. Tuning them used to be relatively inexpensive up to the late 1990’s, and you can get far more power out of them than they were ever intended to make. But it’s almost always at the expense of reliability.

As VW’s flat 4’s were used for so many years with relatively few changes, by the 1990’s other more modern engine designs were getting a lot more economical, making older VW engine designs relatively uneconomical. But with the build quality of VW’s in general and the cult following meaning far more rear engined VW’s were still on the road than a lot of their contemporaries, some owners started to want a more economical engine, not just a bit more power. In fact what most want is a bit of both – a bit more power than their VW engine, with better economy too, plus better reliability without the constant need to tweak air cooled engines that they are renowned for especially as they get old and worn. This sounds like ‘having your cake and eating it’, yet thanks to other manufacturers developing their horizontally opposed engines far beyond where VW got to, this is totally achievable.

In the 1980’s and early ’90’s this lead some to experiment with converting to Alfa Romeo flat 4’s. These conversions were never very common, and seemed to largely be based on the engines from the Alfasud and the Alfa 33, which had overhead cams. The narrow range of capacities and similarity in power output to some of the VW models means their were not very advantageous, and them still using carburetors meant they didn’t provide the economy and reliability available with injection or engine management either (if that’s possible with 1980’s Italian injection!). Alfa did develop their horizontally opposed engines a bit further, with the injected versions of what were effectively the Alfa 33 engines in the 145 and 146 up to the mid 1990’s, but these hardly seem to have been used in VW conversions at all.

By the time VW stopped building flat 4 engines and rear engined models (outside the South American market) in 1992, their flat 4’s were showing their age. The last horizontally opposed car engines to be pushrod rather than overhead cam. Even the water cooled models were heavily based on design of their air cooled predecessors, which ultimately date back to the late 1930’s. Lots of other newer engine technology had come along in that 50+ years which VW never applied to the flat 4’s, which were still restricted by 2 valves per cylinder and a 3 bearing crank. If VW had continued horizontally opposed engine development, overhead cams, 4 valves per cylinder and a crank bearing between each rod journal would have been the obvious improvements, along with a built in water system rather than the wasserboxer’s external, afterthought mess of a cooling system.

Subaru had been developing their EA series of horizontally opposed engines since the 1950’s, and by the mid 1980’s, like Alfa they were ahead of VW in terms of adding newer technology. By 1984 then new EA82 engine had overhead cams, with carburetor injection or turbo variants, but still a 3 bearing crank like VW’s. All were 1781cc. These did get used in VW engine conversions, but were never very common. Like the Alfa engine conversions the narrow range of capacities and similarity in power output to some of the VW models means their were not very advantageous. Unlike VW though, Subaru were also working on the next generation of their flat 4’s, and it was a new design from scratch, superseding the EA series and with no common parts. These became the EJ series engines, introduced in 1989, for the 1990 model year. They have 5 bearing cranks, so significantly higher rpm limits, and were all overhead cam, with multiple SOHC and DOHC variants over the next 30 years. If VW had continued development of horizontally opposed engines, they would almost certainly have come up with something very similar. Subaru made EJ series engines with a very wide range of different capacities and power outputs.

Subaru’s range of horizontally opposed water cooled engines have become by far the most commonly used engines for transplanting into rear engined VW models for many years now. The first we heard of Subaru parts being used in VW’s was in 1992, with Peter Harrold’s awesome turbocharged 4wd rallycross Beetle and it’s VW engine with Subaru turbo DOHC cylinder heads. It was the late 1990’s before complete Subaru engines started being used for more conventional VW applications though, when they quickly took over from the Alfasud flat 4’s as being the most commonly installed alternative engines (at least here in the UK).

Another appealing feature of the Subaru EJ series engines is that they are still relatively easy to work on. Almost all of the subsequent horizontally opposed engines such as the Subaru EZ, EE, FA and FB series, and Porsche M96 engines (Subaru and Porsche being the only two manufacturers to stick with horizontally opposed engines after the late 1990’s), are anything but simple to work on. The early versions of both the Subaru EE series and M96 both had significant problems too, not that they required work on the engines to fix – the problems often wrote the whole engine off! (snapped cranks in the early EE series, and failed intermittent shaft bearings in the M96).

Also, the EJ series engines fall into a very nice ‘sweet spot’ in terms of the engine management used. On all of the pre CAN bus models, it is sophisticated enough to give the reliability and economy that many considering changing their VW engine for something more modern desire, but also easily separated from the rest of the car (i.e. not reliant on being connected to many other systems which will not be in the VW. It is not impossible to use some of the CAN bus engine management systems in VW’s, however you should put considerable thought into this before purchasing one. It is considerably more complex and expensive than using a pre CAN bus model, and often comes with a lot of mechanical complications which don’t exist with the earlier engines too

We have been involved with Subaru powered VW’s since 2002 – longer than anyone else except one company in the UK. There are quite a few ways that Subaru engines can be installed in VW’s, some better than others. Our objective has always been to make products to do the job to the highest standard possible. There have been plenty of others out there with the rather opposite objective of investing the absolute minimum about of money in making a Subaru engine run in a VW, cutting every corner you can imagine (plus plenty that few would ever imagine), while charging an awful lot for them. Therefore not all Subaru engine conversions are the same. A lot are installed to very very low standards. The worst ones in the UK at least are generally not amateur DIY attempts, but the work of ‘specialists’. So do your homework up front if you’re looking for someone to do installation work for you in the UK.

If you’re looking for products to install Subaru engines into VW’s which have been continuously developed by professional engineers for over 20 years, you’re at the right place.

Love your classic rear engined VW, but don’t love it’s fuel economy, engine reliability, the constant tweaking that old VW engines require, or it’s lack of power as much? Whether it originally had an air cooled Type 1, Type 4, wasserboxer or a horrendously under-powered diesel that just can’t keep up in modern traffic, the number of owners who see constantly tinkering with engines as a part of their hobby is decreasing. Many younger owners have grown used to more modern vehicles which just work year after year with minimal maintenance, and for many older owners who still drive classics the appeal of doing so isn’t exactly because they crave having to carry a tool kit around and tweak carburetor linkages, etc constantly!

Then add in the fact that as the original VW engines get older, the amount of top quality parts available for them decreases. Even many of the OEM brands who could be totally relied on say 20 years ago to provide you with the exact same parts that they supplied to VW have now moved production to where labour us cheaper, and quality standards are not as high a priority. The result is that it continuously gets harder and more expensive to build and maintain VW’s older engines (in particularly the horizontally opposed ‘flat 4’s’) to the sort of standard which used to be normal.

The days of always having a choice of good used VW engines, or inexpensive rebuilt engines have ended, and it can cost many thousands of pounds to rebuild a standard VW engine to a reasonable quality. Even if you manage to get all new old stock parts, so end up with a genuinely ‘as new’ engine, how happy will you be with what that investment gets you? If you want a bit more power too, yes a lot of the VW engines are quite tuneable, but doing so gets very expensive very quickly, and always comes at the expense of reliability. Will you be happy with:

  • the low 20’s UK mpg ( mid teens US mpg or L/100 km) that is the best economy that you can expect from many of them
  • the inability of some models to pull up steep hills when moderately laden without dropping down to 2nd gear
  • the constant need to mess with the timing, carburetor(s), etc that anyone familiar with especially the air cooled models will know well

If your answer is not very happy, then you should consider swapping to a more modern engine. Even a lot of people who used to be die hard VW originality types have come around to see that the original VW engines are not always the best option these days. All it usually takes is travelling with friends with who have more modern engines in their classic VW’s, or one too many expensive failures of rebuilt or tuned VW engines. We hear stories like these all the time when new customers enquire about parts for an engine conversion project.

All of the rear engined VW models were originally designed for flat 4 engines. Yes, some of them can sort of fit some other engine configurations in them, such as the inline 4 diesel T25 / T3 / Vanagon models or the water cooled South American built inline 4 petrol T2c models, but they never look right. With all of them even the inline engine installations done by VW look like a compromise – they’ve had to move things around such as tilting the engine over at a large angle to get them to fit. Very few engines can ‘look right’ in a rear engined VW engine compartment. Some don’t care what it looks like, but others do.

VW ended their horizontally opposed engines with the last of the rear engined VW models in 1992 for European production. If they had continued, the obvious changes to make would be to make the crank 5 bearing instead of 3, and to make the cylinder heard overhead cam. Technology which was being applied to pretty much all new engines back in the late ’80’s / early ’90’s. That’s pretty much exactly what Subaru introduced 2 years earlier with their EJ series engines. They were also the next development of an older water cooled flat 4 design which was originally a pushrod engine – the EA series which they’d made since 1966, and the later versions of which had already gone to overhead cams. Within a few years there was a wide range of capacites and power outputs available, in the sort of range which would appeal to many wanting to do VW transplants. Previously Alfasud engines were sometimes transplanted into VW”s but they had a very limited range of capacities and power outputs, from a 1.2 to a 105 bhp 1.5. OK in a Beetle maybe, but not what many would want in a heavier bus.

Subaru’s EJ series engines come in 1.5, 1.6, 1.8, 2.0. 2.2,and 2.5 litre sizes, normally aspirates and turbocharged, with many different power outputs from 90 bhp to 300 bhp as standard. They can look very ‘right’ in VW engine compartments, especially when installed using well designed products – a badly done engine conversion can make any engine look a mess!

A Subaru engine can give what most customers are after out of their engine conversion project. Modern car levels of reliability with no need to tweak things all the time, with significantly better fuel economy than any of the VW engines can give at either a similar or an increased power output.

The percentage of classic VW owners who have the budget to commission or DIY install an EV conversion is very small, at least here in the UK. Old VW’s are not like some of the old Porsche and Ferrari models that get EV converted, where the engine and transmission that you are taking out are so valuable that if you sell them, that will pay for most or all of an EV conversion. Most are owned by people who don’t have a Ferrari or Porsche owners budget, or anywhere remotely close to it.

Also the current wave of interest in converting classic cars to EV is very likely to be a passing trend, as a lot of the expectations, in the classic VW world at least, are not realistic. It’s all happened before with other power trains. A deluge of internet hype and apparent high amounts of interest in a particular ‘new’ idea, where every man and his dog seemed to believe this is the winning combination that will give them 50+ (UK) mpg in their diesel T25 / T3 / Vanagon. Remember how the internet would have you believe (briefly) that by trying just about every VAG diesel connected to a Porsche 996 or upside down Passat gearbox, one would be found which was insanely efficient, or that the Subaru EE20 diesel flat 4 was hyped as the magic combination that everyone has been waiting for, that would achieve intergalactic fuel economy? Very few of either ever got built, and it’s real easy, as an engineer, to see why. These conversions were based heavily on unrealistic expectations. With the Subaru EE20, that unrealistic expectation was cost. The engines very very highly sought after by Subaru owners, due to the first year or two’s production regularly breaking crank shafts, and writing off the whole engine. That kept prices high, and installing one in a VW for less than £10,000 just wasn’t possible. Plus they ave so much trque that any VW gearbox won’t last 5 minutes. Changing the powertrain doesn’t change the laws of physics. The fact that you’re still pushing a brick with a Cd of between 0.4 and 0.55 (T25 / T3 / Vanagon) through the air. Typical modern EV’s have a drag coefficient between 0.2 and 0.35, with even the huge Rivian R1T being just 0.3. Add in the fact that many owners also want to be able to drive at modern motorway speeds, which tend to be higher than when their classic VW was new. Drag does up with the square of vehicle speed. To achieve the sort of economy that modern vehicles get, you need the drag coefficient of a modern vehicle, but if you modified your classic VW enough to achieve that, it would no longer resemble a classic VW!

Or think of it in terms of speed if you want your VW to go a bit faster. As an example, imagine you have a 1.6 CS non turbo diesel or 1.6 CT petrol T25 / T3 / Vangon. The notoriously under-powered models in which VW fiddled with the gearing to make them pull acceptably up to about 55mph, but in which that 55 mph was also flat out. Using all of their power was essential – they were both only 50 bhp! You swap its powertrain for any with enough extra power and suitable gearing so it’ll run efficiently at 70mph – a very realistic and achievable goal easily met by even the moderately powerful standard models. That’s 27% faster. Therefore the drag will increase by 1.272 = 1.61, or 61%. You will need a 61% increase in power to 1.61 x 50 bhp = 80.5 bhp required to just overcome the drag to be able to get to 70 mph. Or at 70mph 100 x (1 – (100/161)) = 38% of the energy you’re using is just moving air relative to going at 55 mph in the same vehicle. But you’ll get there 21% faster.

Then factor in that most of those who think they have found some magical ultra economical powertrain for their T25 / T3 / Vanagon won’t be wanting to compromise its ability to carry heavy loads and / or tow…… They’re dreamers, seeking something which can’t exist, but who have a seemingly limitless amount of time to discuss why it must be possible on internet forums.

Back to EV converted classic VW’s. At least not until mass produced EV’s are common enough that supply of good, very low mileage, suitable used batteries and powertrains outweighs demand, so the prices drop significantly, the cost of doing such conversions will remain too high for all but a small percentage of VW owners at least here in the UK. Just the amount of bespoke engineered products needed for such conversions plus the large amount of work to install them (to a high standard) means they will cost multiple times what it costs to convert to a better, more modern internal combustion engine for the foreseeable future.

The future of well done, affordable EV conversions for classic cars won’t be in the sort of conversion businesses who get TV series features, etc, converting whatever turns up with no specialist knowledge at all about the majority of the models they work on. Electrically they’re probably OK, but mechanically they’re very much ‘chop shop’ type conversions, where the quality of the work done can not be much higher than Scrapheap Challenge / Junkyerd Wars. This is because for a one off, there can be no budget to properly engineer and develop the conversion to fit well, never mind research the variants of the model so they know that what they come up with will fit all of them equally well (anyone see the Porsche 914 episode where they built the battery frame by welding angle iron all over the engine compartment? – total crap). It’ll be with specialists who concentrate on a very small number of models and go to great lengths to make the conversion bolt in. It’s no different with IC engine conversions.