There is no ‘best’ engine to use for any Subaru engine conversion. This is because different customers have different expectations or requirements. One customers’ ideal engine may be the last thing another customer would want. To be able to choose an engine spec to use, we recommend you start by deciding how many horsepower you are looking for.

Buying a particular engine because it is available, without really considering whether it suits what you need, is generally not a good idea. Many times we’ve seen customers who have bought, or are about to buy a turbo engine because it’s available, but when you speak to them more about what they actually want, a normally aspirated EJ20 would far better suit their needs. Or customers who have mad ideas like buying a turbo engine because it’s available, and attempting to remove the turbo and run it as naturally aspirated. This is insane thinking – if the objective is to have the engine run as efficiently and as reliably as Subaru intended, you need to run it as Subaru intended.

Others sometimes seem to assume that because their 50 bhp VW engine won’t pull them up a particular hill, etc without dropping down to 2nd gear, they need 200 bhp plus to make it nicer to drive. That’s absolutely not correct. In most cases 125 bhp from a normally aspirated EJ20 or 160 bhp a normally aspirated EJ25 (a 250% or 320% increase respectively) is easily more than enough to make it ‘nicer to drive’ / more economical / more reliable, if that is the objective, which it is for probably 90% of customers. It also makes the conversion considerably cheaper and easier to install than a turbo or a six cylinder.

The most commonly used engine by a very long way is the normally aspirated EJ20. Partly because they gives the balance of bhp vs economy that most customers want, and partly because they’re far more readily available than all of the other engines in most markets (they’re probably not the most readily available in the US or Australia, where EJ25’s were more common).

Yes. Engines from automatic Subaru’s do not have a flywheel or clutch so you’ll need to add them. This is the main mechanical part of converting an automatic Subaru to manual spec. There is a bit more involved for some engines if you want to do the job properly. In particular, you’ll need to fit the additional manual only cam belt guide if your Subaru engine is an EJ series from MY98 or later. You can also fit the additional cam belt guide to earlier EJ series engines, but only if you change the oil pump for an MY98 or later type.

Electrically Subaru engine management systems from autos are always different to the manual version, and you need the engine management to run as if in a manual Subaru whether in a manual or an auto VW. This means the harness work  to build an ‘engine management only’ harness for your VW is quite different if the engine has come from an auto relative to a manual, but the total amount of work is about the same, and the cost is the same. There are a small number of Subaru engine management systems which were only ever made for automatics which cannot be reconfigured to run as a manual because the ECU’s do not have the manual software. These include the EG33 and all pre CAN bus EZ30’s. All of the EJ series management systems used in European / ‘Rest of World’ spec Subarus tend to have the manual software. The same can’t be said for all Japanese  and possibly US / Canadian spec models though. Some of them are ‘auto only’ (e.g the JDM EJ204 which has AVCS (variable valve timing), as fitted to MY99 Legacy Lancasters) . These can always still be used in manual applications, but may run with error codes due to them expecting signals from the transmission controller ECU. This is not a problem, as long as you are not also using Subaru cruise control.

This is an example we recently did – a complete re-work on for a customer who sought out help after having multiple electrical problems with a camper they’d bought with a conversion already installed:Previous

You’d probably imagine this was the work of an amateur with almost no idea what they were doing, but no. The owner had paperwork documenting who did this work, not that we needed to ask. We knew whose work this was from the customer descriptions of the problems they had been having before seeing any of it. One of the best known UK ‘specialists’. We’ve seen it all (too) many times before. It was refreshing to see they’d discovered soldering by the time this one was installed – all their early work ‘featured’ neatly taped joins with wires twisted together inside!

Reworking harnesses in this kind of state is not work we really want to do, but there has always been a demand for it. It always costs more than if we’d done the job from scratch. How much more can be anywhere from not much to 50% more. We’ve done some involving re-joining harnesses which have been cut into multiple pieces before which cost far more, but turn down that kind of job these days.

Obviously we’ve picked an example from the worst offender to show here. Don’t assume that because the end result looks neater than the first pic above that the job has been done well. Wrapping harnesses neatly takes almost no skill compared to understanding the circuits inside them.

Try Import Car Parts . They ‘grey import’ a lot of genuine Subaru parts and sell them for less than the UK dealerships. If it’s service parts you’re after, they often stock other brands as well as the genuine parts. If it’s a Subaru thermostat you’re after, don’t buy any aftermarket brand – only use genuine Subaru ones.

If it’s a T25 / T3 Vanagon and you’re in the UK of shopping with UK suppliers, Brickwerks are generally the best supplier. They care about the quality of what they sell, so generally don’t sell some of the awful quality aftermarket parts which the competition are happy to stock.

Apparently the owners of some of the biggest UK aftermarket VW parts suppliers believe they’re ‘offering their customers more choice’, but with some of the worst quality products (for example JP Group’s non plated clutch release shaft for the 091 and 094 gearboxes 1130701000 ), they’re actually just supplying total crap which, in cases like this are regularly not fit for purpose for up to 3 reasons on the same part. When customers return them, even with clear evidence someone has been sanding the parts trying to make them fit, they just put them back into stock and sell them to someone else. If anyone high up at the UK’s two biggest VW parts suppliers should read this, if you didn’t keep buying parts like this (the worst quality aftermarket VW part we’ve ever come across), JP group would either have to stop selling them or fix their multiple quality problems. Nobody who has ever bought one of these will think you’re ‘doing them a favour’ by stocking such junk. If you want to know what’s wrong with them in detail, we can tell you. We developed our own version specifically because of the problems cause by the terribly quality of this part.

We sometimes get customers who have just finished their conversion projects getting in touch to say how pleased, or how surprised they were that ‘everything fitted’, or ‘everything worked’. On the one hand, to us it seems absurd that anyone should be surprised that what they have bought works – they should expect it to fit and work. That’s our objective as a manufacturer. On the other hand, it’s pretty easy to see why they’re surprised, especially if they’ve done any engine conversions or similar major aftermarket vehicle modification work before. The average quality of engine conversion products is pretty low, with many or even most being manufactured by amateurs with no relevant design engineering or product development experience at all, yet marketed as though they’re ideal products. This isn’t just a VW – Subaru engine conversion thing. There are a lot of crude products out there for many other engine conversions too, and in out opinion, its almost always because the outcome of amateur projects get marketed as professional products.

This issue is what got us involved in designing and developing Subaru engine conversion products in the first place. Back in 2002, the products available for installing Subaru engines into VW’s were all imported from either Germany, the US or Australia, with some reselling them (and marketing them as if they were their own products) here in the UK. After looking into all of them, it was clear that they were not what we were after in terms of quality, so we’d have to design and make everything from scratch. Achieving the expected level of quality would not be an issue with our background in vehicle design engineering.

This issue is what got us involved in designing and developing Subaru engine conversion products in the first place. Back in 2002, the products available for installing Subaru engines into VW’s were all imported from either Germany, the US or Australia, with some reselling them (and marketing them as if they were their own products) here in the UK. After looking into all of them, it was clear that they were not what we were after in terms of quality, so we’d have to design and make everything from scratch. Achieving the expected level of quality would not be an issue with our background in vehicle design engineering.

In the UK at least, almost all of the other current and historic ‘Subaru – VW engine conversion specialists’ businesses have typically been well-meaning amateurs who have stumbled into running an engine conversion business as a result of their DIY project. Practical folks, or garage businesses who have stumbled into being engine conversion parts manufacturers as a result of doing an engine installation for a customer. Either way, a significant proportion have no morals, as their businesses have typically been heavily based on copying the work of others, or in some cases claiming the work of others as their own. On the one hand this makes sense – without an engineering design background, it’s the only way they’ll ever make products. Being ignorant of either tolerancing in general or the correct tolerances tolerances to use, etc, they’ll be unaware that there is more to reverse engineering others’ products than that. But on the other hand, should they be marketing the results as tough they are professionally engineered products? Err, no, yet they do. Two have certainly not been so well meaning (repeatedly not being honest with their customers about the spec of spec of engine they have installed, and dealing with the legal consequences – we were asked to be expert witnesses by the customer’s lawyers, but they settled right before it was due to go to court), or making impossible claims about their conversions such as quoting impossibly low prices (not sure how they ever thought that could work – unsurprisingly they didn’t last). The lack of a professional engineering backgrounds amongst many making engine conversion parts for VW’s in the UK stands out to engineers. Not at the fitter / technician / fabricator sort of level (many of them are undoubtedly practical folks), but at the level of professional design engineering and automotive test and development experience. Man + welder ≠ engineer. The average customer may struggle to spot it though, which is totally understandable. Too often they get taken in by shiny marketing and a constant social media presence of the sellers, and believe they’re buying professionally engineered products, when often they’re not.

To design and manufacture products for engine conversions to as close OEM standards as is practical in low volume manufacturing requires professional design engineering background, ideally an automotive one, like we have. Many competitors seem to subcontract this to engineering companies who make things for them – i.e. machinists and fabricators, but that is really missing the point. Without the detailed understanding of the systems that they are working on that only a professional engineering background will give them, they will never be able to specify exactly what it is they need their supplier to do in sufficient detail to be able to end up with a range of good products. This really shows with a lot of the products and services offered by competitors. A very high percentage of them are very amateur products, of the type typically made by enthusiastic DIYers doing their own conversions at home, but marketed as if they are properly researched and developed by professional engineers.

Without a suitable background engineering or product development, those with backgrounds in other industries attempting to manufacture products for the engine conversion world often seem oblivious that what they have come up with isn’t even remotely close OEM standards, because they don’t understand what product development is. We have seen examples of new products being offered for sale where if you search hard enough, the manufacturers themselves have already documented having never done any kind of testing at all. They were effectively charging all of their early customers to unwittingly participate in their product development program. When some products for Subaru gearboxes appeared on the market, overnight being pushed on all of the major engine conversion forums in the world, a read of a (then) 30 page thread on thesamba.com showed that they had never been used in a running vehicle at that point. Yet the marketing conveniently did not mention this.

A shiny, yet often suspiciously anonymous web site with little or no technical information, yet a near constant social media presence is very far from a guarantee that you’ll be getting professionally engineered products in this industry, unfortunately. Those with a professional automotive engineering background approach the design and development of products from a completely different level of attention to detail than those who have stumbled into the Subaru engine conversion products manufacturing world from another background. Garage owners, etc. are always practical folks, but they’re not professional engineers. Unless they studied engineering and have relevant professional experience working on something similar, they’re amateur engineers, and it really shows.

See below for examples of the worst work we’ve seen:

Examples of the unbelievably bad quality work we have seen from long standing, mostly UK businesses who promote themselves (often very heavily) as ‘Subaru engine conversion specialists’. None are the work of amateurs – all are from those who promote themselves as professional specialists. If you have any knowledge of engines or engineering, you’ll probably be shocked and / or amused by many of these, but they’re all real, and not one offs:

  1. The idle speed control airflow blocked off totally on the Phase I engines by holding a coin in the hose to the valve with a hose clip. Then jacking the throttle valve stop screw open to allow air into the engine so it can sort of idle (the screw never needs adjusting under any circumstances on any Subaru engine, unless someone tries to use it and an alternative to the idle speed control system which they have disabled for no apparent reason)
  2. Removing all wiring for the cold start circuit for many years, and trying to fob off customers with excuses when they cannot start their VW in freezing temperatures. We flattened the usual battery plus a tractor sized battery unsuccessfully trying to start a local guy’s dodgy conversion in which the cold start circuit they had removed. We later got so fed up with their customers getting in touch wanting us to fix this incomprehensible error that we published how to do it on a forum the company owner frequented.
  3. Solid core (i.e. not flexible) domestic mains wiring used within Subaru engine management wiring
  4. Consistently very neatly taped joins where wiring harness modifications have been made, which always contained wires just twisted together, never soldered or crimped.
  5. Subaru wiring harnesses which have clearly been chopped into multiple parts by someone who couldn’t be bothered to remove them intact, then joined back together using only the awful ‘pre insulated’ red / blue crimp terminals, all exposed to the weather
  6. Consistently never fitting vehicle speed sensors for many many years, then trying to fob off all customers who complain about the symptoms which this unavoidably causes (which can be so annoying as to make certain engine management systems virtually undriveable) with total nonsense excuses
  7. Consistently removing the thermostats because they had no understanding of how the cooling system worked of the need for a heater bypass, and this was the only way they could get the coolant to circulate
  8. Impreza and Legacy ECU’s which are not remotely weatherproof (they’re a PCB in a perforated steel box) regularly mounted on the ‘shelf’ by the battery in bay window buses and T25 / T3 / Vanagons – directly below the vent behind the rear window, which rain can and does enter through
  9. Coolant plumbing to the front mounted radiator in Beetles made from numerous sections of used, rusty exhaust pipes welded together (yes, really – we’ve only seen one example of this, but the owner had had the whole conversion installed by one of the regular offenders)
  10. Systematic removal of all diagnostic features on Subaru engine management systems
  11. 1700 or 1800 type 4 bus clutches installed for Subaru turbo engine conversions using adaptor plate / flywheel kits to join them to the VW gearbox  – they don’t have anywhere near the required torque capacity for even the normally aspirated EJ20 and EJ25 engines, so can’t last 5 minutes with a turbo
  12. Adaptor plates which hold the engine and gearbox out of alignment by 14 (yes, fourteen) times the maximum engine to gearbox alignment tolerance we use on our bell housings. Not surprisingly, this causes big problems
  13. Consistent major problems with the power supply wiring to Subaru engine management, including no fuses, seemingly random fuse assignment, and drawing all of the power for the engine management through the VW ignition switch (VW ignition switches are not rated for anywhere near that much current, and quickly fail as a result)
  14. Regular incorrect connection of the memory backup wire of some Subaru engine management systems to an ignition switched power source. This means that every time the engine management is off for more than about a day, the ECU loses all of learned ignition map, so always starts from the most retarded map settings, reducing performance and fuel economy. Given that it takes more than a tank of fuel for the ignition map to adapt fully to the fuel you use, the map will never fully adapt, as it gets reset every time you don’t run the engine for a few hours
  15. Exhaust systems where the entire weight of the system is hung from the plastic cam belt covers via their M6 screws. Unsurprisingly the cam belt covers don’t like that much, and the first time we came across a customer of this system the mounting system had already failed. Probably the most blatant example of design by somebody with no clue what they are doing that we have ever seen.
  16. Engine mounting sub frames in VW buses made from a chopped up Subaru front sub frame, plus over 10 pieces of random, mismatched angle iron and box section (clearly scrap metal) stacked to fill the gaps between it and the chassis rails, then all welded together (including to the chassis). Most of the contraptions built on Scrapheap Challenge / Junkyard Wars would be much better built than these.
  17. Engine mounting sub frames in VW buses made from a chopped up Subaru front sub frame, plus over 10 pieces of random, mismatched angle iron and box section (clearly scrap metal) stacked to fill the gaps between it and the chassis rails, then all welded together (including to the chassis). Most of the contraptions built on Scrapheap Challenge / Junkyard Wars would be much better built than these.
  18. A cooling system which has zero chance of cooling at motorway speeds in the summer without being entirely reliant on the fans being on all the time. ‘Featuring’ attempts to cover their work in terms of warranty regarding overheating by hiding maximum temperature tell tales on the engine. Then when the next customer tries to claim warranty because their engine seized, they can uncover the tell tale, and ‘prove that the customer has allowed it to overheat’.
  19. Offering fabrications such as engine mount crossmembers for sale, but when a customer tries to order one, they’re asked to deliver their VW to them so they can fabricate it in situ! Clearly no understanding of fabrication or fixturing at all….. but that would maybe be a bit much to ask from the same company who have previously made cooling plumbing from scrap exhausts, and bridged the gap between a Subaru sub frame and VW chassis rails by filling it with random crap welded together.
  20. Consistently never putting antifreeze in the cooling system of their conversions. The cooing system that the offending company fits into all of their air cooled VW bus models cannot work without relying in fans, so after much struggling their customers often get in touch with us wanting a system which works. We frequently end up modifying their Subaru coolant manifold to fit in reverse as part of the solution, and the original installers work is immediately identifiable because of a couple of strange things they do to the coolant manifolds. Pretty much without fail the inside of the aluminium casting is entirely rust coloured – a sure sign it’s been running with no antifreeze.

All but a few of these are examples of the work of one UK company, and are things we’ve seen multiple times (except where it says so above). We don’t go looking for this stuff (we don’t work on customers vehicles at all). All of this finds us when the unfortunate customers of awful products and workmanship go looking for solutions to the problems with their conversions. For many the above, there is no possible other explanation other than an absolute lack of understanding of the systems being worked on, combined with total contempt for their customers in the case of the main culprits. The lack of engineering knowledge required to achieve pretty much all of the above is beyond shocking – anyone doing work at this level has no business manufacturing anything.

We were asked to be expert witnesses for the defence in a court case against the main purveyor of this crap once, when they’d installed a totally different spec engine to what they had told their customer they were fitting. We declined, not wanting any involvement with them or their terrible work. The case settled out of court involving quite a lot of compensation, and we provided quite a few products to to owner so he could re-do the work properly. Multiple others have taken legal action against the same company apparently. Given the many many years the above examples have been seen over, an absolute lack of learning from their numerous mistakes seems to be involved too. Hopefully you’ll agree that most of the above are so bad you couldn’t make them up? More than once we couldn’t believe that many of them could possibly be the work of a business, until we discussed them with the vehicle owners, and later seen the same bodges multiple times with the same stories behind the work done.

The company responsible for most of the above is still going. It’s not difficult to find out who they are – scratch beneath the surface and they have an exceptionally bad reputation (deservedly so) which is very easy to find. Yet they still manage to find customers to con into spending vast amounts on beyond awful work with them. Shop very carefully if you are looking to have a Subaru conversion installed. We have never done business with them, not wanting anything to do with this level of workmanship.

Overall, their work is an interesting insight into both the power of advertising, and how little homework many people are prepared to do before choosing who to spend a lot of money with.

This applies not only to the Subaru engine conversion world, but the entire rear engine VW modification world, and I suspect many other car ‘scenes’ too. Examples would be well over half of the suspension, power steering and brake conversion products which we see being made for the VW scene in the UK and marketed at VW shows, etc. Fabricated dropped spindles on which the welds are cracked before they have even been installed, or electric power steering conversion kits which remove all of the collapsibility which VW designed into the steering column anybody? No thank you.

We have product liability insurance covering all of our products (except sales to the US). It’s more than clear that the purveyors of most, probably all of the awfully engineered products we’ve mentioned in this article have no comprehension of what product liability is. Product liability cover as a small business manufacturing components for vehicles which will be used on the road is exceptionally hard to get. Most business insurers won’t touch it, and with the crap mentioned above being churned out by self-proclaimed ‘specialists’ with no backgrounds in engineering design and products development, it is not hard to see why.

The moral of this story is do your homework before choosing a company to install a Subaru conversion for you in the UK. Look deeper than whoever is constantly on Facebook promoting themselves, and at least Google them followed by ‘reputation’

If ‘waterless coolants’ were as amazing as their manufacturers claim, they would publish the specific heat capacity data for their products, as this would be the best marketing possible.

Specific heat capacity is a direct measure of the ability of a substance to move heat to move heat (a measurement of the energy required to change the temperature of a given amount by a given temperature), and water has one of the highest values of any common substance which is suitable for engine cooling. The antifreeze / corrosion inhibitor products required to make water into a suitable engine coolant have lower specific heat capacities than water, so the actual specific heat capacity of a water / antifreeze mix depends on the mix ratio. However, the mix ratios usually used don’t decrease the figures too much, as shown below:

Water / Ethylene Glycol antifreeze coolant mixture specific heat capacity and typical use in engines:

Ethylene Glycol Antifreeze % by weight:Specific Heat Capacity, cp (kJ/(kg oC)), at 80 oC:Typical usage:
04.19 
104.14 
204.05 
303.93Minimum ratio, moderate climate
403.80 
503.66Most climates
603.49Maximum ratio, very cold climate
703.31 
803.12 
902.90 
1002.68 

So called ‘waterless coolant’ products are based on almost pure ethylene glycol or propylene glycol, and have a specific heat capacity of just 65 – 70% of that of a typical water / antifreeze mix. Interestingly they have both also been banned in a lot of motorsport, for multiple reasons. They are flammable, and many times more slippery than water or normal water mixes when spilled on a road or track. Some have even banned all coolants when mixed with water due to the latter, meaning only water is allowed as a coolant on their tracks.

There are plenty of other concerns about ‘waterless coolants’ if you delve deeper into the subject. They include  the effects of the considerably higher viscosity on cooling systems not designed for them, and increased engine temperatures.

If you are wondering why we have an opinion on this, it is down to a customer having used the most common waterless coolant brand in his bay window bus conversion which used our under floor radiator system. By then the radiator system had been on sale for many years, and was well proven to cool way in excess of a normally aspirated EJ25 engine in a UK climate without relying on the fans coming on any more frequently than you would expect them to in a production car. The customer with the waterless coolant had constant problems with coolant temperature right from the start, and we quickly came to the conclusion that everything was plumbed correctly. He had followed the filling procedure, had a genuine Subaru thermostat which we had proven worked correctly.

Effectively, we’d eliminated all the other variables except the coolant, and recommended that the customer replacing it with conventional coolant was the only way he would find out whether the coolant was the cause with certainty. He was very reluctant to do this, having spent many hundreds of pounds on the coolant and the flushing chemicals sold by the waterless coolant supplier to clean the system out prior to filling. What finally convinced him to try what we’d been suggesting was interesting. He’d fabricated something and wanted to cool it quickly immediately after welding. Anyone who fabricates or otherwise heats steel parts regularly soon gets a feel for how effective water is at cooling them fast. The first thing that came to have for him to cool the part was a jar of left over waterless coolant. He plunged the part into it, stirred it around for a couple of seconds, and then burned himself on the still very hot part, knowing that water would have cooled it to a safe temperature in that time.

He drained the waterless coolant from his bus, replaced it with water, and it cooled as it should right away. An expensive lesson learned, and very interesting feedback for us.

If you’re still tempted by the marketing hype / BS from the purveyors of waterless coolant, try looking up the prices of the base chemicals which they’re based on (they’re readily available online), and then ask yourself how they justify the insane prices. You’ll see 15 litres of ethylene glycol is about £60 – £75 including VAT and shipping (2022 prices) – they’re not particularly expensive chemicals. ‘Waterless’ coolants for modern cars are ‘snake oil’ products, dependant on hype and marketing to sell unsuitable products to the unsuspecting. Follow the science, not the hype. If they were so superior for engine cooling, why are the manufacturers of hypercars, etc, where no expense is spared manufacturers not using them, and why have the biggest OEM’s who have the biggest R&D budgets not switched to them? Some of them kind of have their industrial applications, for example where ethylene glycol can’t be used because of its toxicity (food industry, etc, environmentally sensitive applications, etc), propylene glycol is used. However, it’s not usually used pure or near pure, but significantly watered down because the water massively increases the specific heat capacity in all applications which allow it.

Since our research for the above, which was many years ago, when nobody seemed to have measured the specific heat capacity of these ‘waterless coolants’, they now have. We based our ’60 – 70% of that of water’ on what their ingredients are, but now a company called No-Rosion have published their test results. They also make an alternative engine coolant, but theirs is, unsurprisingly, water based. See the No-Rosion Waterless Coolant test results – they confirm out assumptions as being correct (64 – 68% of the specific heat capacity of water), but go into far more detail.