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When you're building a modified engine you need to select every component with care. You also need to be aware that almost all aftermarket components will need some sort of modification / finishing before you can use them. This even true of some genuine VW parts, for example, I've found that the fins on genuine cylinder heads often need to be trimmed before they will fit into genuine cylinder head tins.
If you're going to build a modified road engine the crankshaft needs to be counterweighted. This is the only way to guarantee a long engine life when the engine revs are increased. Counterweighted crankshafts are available from a number of sources but most are forged in China and there are always questions marks about the quality of the materials used. I personally have nothing against Chinese manufactured products, China is where most metal components are cast now, I would bet that the crankshaft in your every day car was forged in China.
One name that keeps cropping up when sourcing a crankshaft for your VW is DPR Machining. They take a standard VW crankshaft, weld on counterweights and add material to the con-rod journals to increase the stroke as required by the customer. The material is added to the outside of the journal by welding then cut away from the inside of the journal to increase the stroke. They are so good at it that the crank I received from them still had standard sized main bearings. They will re-grind the main bearings if necessary, the crank I received measured accurately and was perfectly straight, I did check it.
If you are going to fit a counterweighted crank you might as well fit one with more stroke, with a few considerations. Standard stroke for a 1600 cc VW engine is 69mm. This was to be a modest engine making the most of my single point injection system. Strokes above 74mm are likely to require the crankcase to be clearanced for the extra stroke. If this engine were to go into production this is an extra process that would need to be performed on every engine built incurring an additional cost. Also the method DPR use to extend the stroke of the crankshaft will ultimately weaken the crankshaft, cutting away too much material from the inside of the con-rod journal will ultimately lead to weakening of the crankshaft. I decided to stick with a stroke of 74mm for longevity and to reduce operations to the case. It is essential that the crankshaft, flywheel, clutch pressure plate and crankshaft pulley are dynamically balanced before being installed in the engine.
Either a stock weight or lightened flywheel can be used. I feel there is little point running a lightened flywheel in a camper. I have had issues with cast flywheels leaking oil at the flywheel so will always try to source genuine VW flywheels for my engines. DPR will supply a genuine flywheel, 8-doweled and fully balanced to their crankshafts on request.
The crankshaft pulley is also the trigger wheel for my fuel injection system is based on a steel pulley supplied either by Gene Berg or CB performance. The pulleys are machined to create the 36-1 tooth arrangement commonly used on fuel modern injection systems. They are of superb quality and rarely need any material to be removed to balance them. A steel pulley will absorb harmonics in the crankshaft that have been found to dramatically reduce the life of your engine bearings.
With an engine of this specification a stage 1, 1700 lb clutch pressure plate is required. This will give a slightly heavier pedal than stock but it is only just noticeable. This is paired with a solid (not sprung) clutch centre plate.
Most aftermarket engines use either 90.5mm or 94mm barrels and pistons. As the piston size goes up the fins actually get shorter, the cylinders still have to fit into the same space. For this reason 94mm pistons are not recommended for installations into heavier vehicles like vans.
Cylinders of this size require machining of the case and as soon as you start machining a case you need to remove all the gallery plugs the make sure none of the swarf you’ve created has found its way into one of the oil galleries. This is time-consuming and hence expensive. One manufacturer has recently come up with a new size of barrel and pistons. The pistons measure 88mm the same as the old 1679cc kits you used to be able to buy but the’ve put them into a cylinder with the same size spigot into the cylinder head as the 90.5mm cylinder heads use. This means they have the thickest wall of any of the aftermarket cylinders – they are thicker than the standard 85.5mm 1600 cylinders. This should enable them to make a perfect seal at the cylinder head end and stop them going out of round as 92mm cylinders are prone to. The bottom spigot that goes into the case is the same as the 85.5mm cylinders so there is no need to machine the case on that side. An engine with a 74mm stroke and 88mm barrels and pistons has a capacity of almost exactly 1800cc’s and should in theory have a life equal to or greater than a standard engine thanks to its counterweighted crank and thick walled barrels.
Standard con-rods would almost certainly be strong enough for this specification of engine but with good quality I-section con-rods being available from both Scat and CB Performance it seems unwise not to take advantage of them. The use of ARP2000 rod bolts makes case clearancing almost always unnecessary. After all the failure of a con-rod will completely destroy your engine. Standard length I-section con-rods will be used on all of my 1800cc engines.
Crank cases are a source of debate amongst engine builders. New cases are currently available in two materials, aluminium and magnesium. All original German engine cases were magnesium, the material was light and easy to machine. An aluminium engine case sounds like it should be an improvement on the original part. Aluminium is inherently stronger than magnesium which is presumably why VW choose to use it for the type 4 engine, the last air-cooled engine produced by VW. I’ve used an aluminium engine case on the 1800cc test engine I currently have installed in my camper. I have to say I am not impressed with the quality of that case, the finish is very poor and the material itself doesn’t seem to be as strong as the original magnesium part. So far it has held up OK and isn’t a cause for concern but I think in the future I will opt for the magnesium equivalent when they are available. Unfortunately the supply of cases is somewhat sporadic, some times only one or other material is available. At the time of writing there are shortages of both types of case. I aim to setup a direct source of supply with Autolinear, the manufacturer of all new cases to try to ensure a consistent supply of cases.
I am not against the re-use of an original German or Brazilian case but all German cases are now at least 44 years old and there are very few new cases out there. A good quality line bore can bring a old case back to usefulness but when you factor in the cost of stripping the old engine and all the processes required to return it to a useable state it doesn’t make economic sense in most instances. There might be a small cost saving to re-using an old case but there is always the risk of missing some small failure point which will ultimately lead to the failure of an engine or at the very least make it necessary to transplant all the internal components to an alternative case at some point in the future.
Cylinder heads are another area where there are multitude of options. One of the key factors in the development of this engine is that it should be a direct replacement for the original. In that sense it should allow the factory heat exchangers to be retained. Many engine tuners will tell you that if you want to keep your heat exchangers you must keep standard sized exhaust valves, at the most only increase them by 1mm from the standard size of 32mm. I have yet to confirm this but am willing to take their advice until I am able to test it for myself. The standard twin port 1600cc cylinder heads have always suffered from cracks forming between the valves and between each valve and the spark plug hole. Standard cylinder heads use spark plugs with 1/2 inch long threads. This is now pretty much unheard of in modern vehicles, most now use longer plugs. Many manufacturers now offer cylinder heads that use 3/4 inch long spark plugs for the VW air cooled engine, currently this is the best cure to cracked cylinder heads. I have found a couple of good sources for cylinder heads that meet these requirements.
Aircooled net offer a cylinder head they call an ’L3’. This head has the afore mentioned 3/4 inch spark plugs, standard sized valves but with a 3 angle valve job and heavy duty single springs. Wherever possible I am trying to source parts that require minimal modification when they are received by my business. If I have to re-work a product I have no choice but to pass that cost onto the customer. What about porting and polishing? I have no doubt that to get the very best out of any cylinder head you could improve it by porting it but at best at this level of performance you are only going to get up to a 5% improvement and there is always a down side. Opening out the ports of a cylinder head reduces air speed. You will get more ultimate power at the expense of bottom end torque. Extra power is great for discussions with your mates but for a long living engine that is nice to drive it is torque you want. What would VW do? They would specify the right part in the first place, if their customers wanted more performance they would fit larger pistons or a crankshaft with a longer stroke.
Cylinder heads I buy in will have the valves removed, if necessary the valves will be machined to remove excess material as recommended by Bob Hoover in his article , see link below.
As required any casting flash will be removed from inlet and outlet ports with the emphasis on making all ports the same rather than opening them out to their maximum. The valves can then be replaced and the volume of the cylinder head combustion chamber checked. As required the cylinder heads will be machined for the cylinders to be used and to get the compression ratio to the required number. It is critical that all combustion chambers have exactly the same volume otherwise compression ratio will vary from cylinder to cylinder and performance will be compromised. While the valves are out their valve seats should be opened up where necessary and the area around the valve opened out as far as possible to ‘de-shroud’ the valve. This will give maximum performance per pound invested.
The oil system is one area where the VW engine can definitely be improved. VW specified oil changes every 3000 miles, such short intervals was simply down to the lack of an oil filter. As oil is circulated through an engine it picks up contaminants, mostly carbon from the combustion process. With no oil filter to remove them the contaminant will build up until they prematurely wear out the engine bearings. As all new cars have an engine oil filter, in my opinion, the addition of an oil filter is mandatory on anything but a very stock engine.
All oil filter installations will require the use of an aftermarket oil filter mount. Most filter installations are fairly horrible with the filter mounted to the left hand bumper hanger. Flexible lines then connect the oil pump to the filter and the filter back to the engine case. I’ve done this myself with bespoke stainless braided hoses. Within a few weeks the whole thing is inevitably dripping with oil, the stainless lines are impossible to clean. The oil pipes run through exactly where the heat exchanger connector tube to the fan housing should be, it’s a horrible messy compromise. One of the main sources of leaks is the tapered fitting most installations use to feed the oil back to the case. Because they use a tapered thread you can never fully tighten them, the fitting comes loose then once the oil is under pressure it finds a gap and runs down the oil lines then drips onto your driveway and garage floor.
I’ve developed a bracket that replaces the left hand tin that normally goes behind cylinder no. 4. A rigid pipe connects between the oil pump cover plate and the oil filter mount. A short straight pipe then connects between the filter mount and the return tapping in the case. The case is tapped behind the crank pulley in the usual way. The filter doesn’t encroach on the space required by the left hand heat exchanger and can easily be changed without making a mess or removing the rear valance of a van. Because everything is contained within the confines of the engine it should fit any aircooled application be it a van, Beetle, Type 3 or Trekker. Some installation may require a head shield to be fitted between the oil filter and the exhaust. Where this is required it will be supplied with the engine.
If you do use your VW in cold weather there is something else you should consider. When the oil is very cold it will be very thick and even the standard oil pump can easily generate more than 100 psi. The thick oil won’t pass through the filter so easily, in some cases filters and oil coolers have been known to explode, usually this is because the rubber seal has been forced out by the oil pressure. It makes a huge mess and can empty your sump of oil in a few seconds. One possible fix is to use the expensive and fairly large Fram oil filters but even these can have the seal blow out. Gene Berg has been selling an oil pump cover which incorporates an oil pressure release valve for many years. When the oil pressure reaches a predetermined value, usually around 60 PSI a valve in the pump cover opens and returns excess oil harmlessly to the oil sump. Since fitting one of these covers I have not had any issues with exploding oil filters. Oil pump cover plates incorporating pressure release valves are now available from a number of suppliers. All the ones I have tested have worked perfectly. My test engines are fitted with an oil pressure sensor so I can constantly monitor oil pressure.
There are a number of oil pumps available for the VW air cooled engine. The standard pump used 22mm long gears and was all a stock engine needed. In a modified engine we are using more revs so a slightly larger oil pump is always a good idea. It has been demonstrated many times that pumps with 30mm gears are unnecessary and in most cases will over pressurise the oil system leading to blown oil coolers and puddles of oil on your garage floor. I always fit aluminium, Shadek oil pumps to my engines with 26mm gears, never a cast iron or steel pump. Cast iron doesn’t expand at the same rate as the engine case so is likely to feed oil back into the engine case rather than to your bearings. All engines will be fitted with an oil pressure release oil pump cover.
Something that has come to light in recent years is occasionally valve rockers and cam followers have been known to wear prematurely. I’ve disassembled rockers to find tell tale marks that indicate a lack of oil. This is almost always to the rockers on the right hand side of the engine (cylinders 1 & 2). The cause of these issues is a lack of oil getting to the right hand case half. All of the oil system apart from the pickup tube is in the left hand case half. Oil only gets to the right hand case half by passing through a tiny channel around the back of the middle camshaft bearing. A 10mm oil gallery leads to this bearing and another 10mm gallery goes from it to the cam followers in the right hand case half but the channel around the bearing only measures about 3mm x 4mm. In all modified engines it is highly recommended to improve the oiling to the right hand case half. The simplest way to do this is by widening the channel behind the centre cam bearing being careful not to make it any deeper. There is very little material around the channel and when the case halves come together we need to create a passageway for oil to travel across without escaping into the sump. Bob Hoover has written a lengthy article on this subject. He goes as far as to drill a second oil gallery in the rear cam bearing. This is risky as it is possible to destroy a new engine case and unnecessary unless you expect to spend many hours sat with your engine doing more than 5000 RPM. Bob calls these mods HVX mods, please take a look at his article via the link below
The final area to be improved is also detailed in Bob’s article. He recommends a number of modifications to the valve rockers to guarantee sufficient oil reaches the rockers and cylinder heads. This can be done to stock items but as the rocker shafts will be replaced with bolt together ones it makes sense to use parts already modified in this way. These are available from the usual parts suppliers if you know which parts to look for. All my engines will be fitted with bolt together rocker shafts and rockers modified to give a better supply of oil.
I’ve fitted my test engines with an oil pressure sensor after the oil filter. I drill out one of the case plugs and tap a thread to enable the sensor to be connected. The sensor is wired to a spare input of the ECU. The oil pressure gauge can then be added as an additional device on the gauges screen. If you want to connect a laptop or tablet to the ECU you can have oil pressure as a gauge for a modest additional cost.
Camshaft selection is critical in the design of any engine. The stock camshaft is very restrictive and limits maximum RPM to about 4800. By that point you are well beyond the point of maximum power, about 4000 RPM. As the engine uses stock sized valves there is little point fitting anything that’s designed to rev above 5500 RPM so the choice is really between an Engle 100 and and Engle 110. In a heavy vehicle like a camper you want torque rather than power so the 100 would be a good choice. In a lighter vehicle like a beetle, trekker or type 3 the 110 would work better. I always use cam followers from Scat or Engle. The quality of those made in Brazil is awful, the surface finish being very poor.
Any engine that runs more RPM than stock needs stronger valve springs, these will necessitate the use of stronger pushrods. The standard length, 5/16” chromoly pushrods sold by Scat work well in this engine. They are a little noisier than stock pushrods but are necessary when using stronger springs and an aftermarket camshaft. When using chromoly pushrods the valve clearances can be reduced. I set them to 0.05mm rather than 0.15mm specified by VW.
For those people that want a completely maintenance free engine a hydraulic cam followers can be installed. A kit containing all the parts required is available from Mofoco. Installation of hydraulic tappets negates the requirement to check your engine’s valve clearances. Once they are setup they never require adjustment. Hydraulic tappets have got a bad rap in VW circles as there have been issues with those fitted to type 4 engines. If they are going to work properly it is essential to use an oil filter and to make the improvements to the case oil galleries described in the oil system section above. Mofoco have been selling hydraulic cam follower kits since the 1970’s and are extremely confident in their product.
It has to be said, the cooling system of the aircooled VW engine is a bit special. We say it is air cooled but actually a lot of the cooling is done by the oil. Having said that, try taking off the fan belt and see how long it takes for the cylinder head temperature to reach 150C, you’ll do well to get to 5 minutes even at idle. There is no doubt that the ‘dog house’ oil cooler is the best solution VW came up with, I haven’t seen an oil cooler setup that works better. We call it a dog house as it sits outside of the fan housing. When VW changed to the dog-house cooler they changed the cooler material from steel to aluminium, aluminium being a much better material for dissipating heat. This necessitated the installation of a second pressure release valve in the case. The function of the second valve is to allow oil to bypass the oil cooler when it is thick and cold.
VW bolted a small piece of metal to the back of the dog house oil cooler to fill a gap between the fan housing and the oil cooler, these are often omitted. Bob Hoover claims that the addition of this bit of metal can lower the oil temperature by up to 20 degrees. People have started calling the piece of metal the ‘Hoover bit’ as a result. He has a point, without that part there is a huge gap between the fan housing and the oil cooler. There needs to be some gap or you would never get the fan housing over the oil cooler but it is huge. I recently experimented by adding a strip of metal to the fan housing to reduce the gap. I immediately noticed a significant reduction in cylinder head temperature as a result. I plan to carry out this modification on all the engines I build.
I’ve used Scat tinwear on my latest development engine as I was told it is the best available. Out of the box, I’d say it’s OK, but there were various areas where I felt it needed to be reshaped and trimmed to fit properly. There were a couple of areas where it was a bit short and could have done with the addition of some of extra material. The cylinder head tins VW manufactured have a bit of metal welded to them to cover the gap between the cylinder pairs, I haven’t found any aftermarket cylinder tins that incorporate this feature. You can bet there was a reason VW added these extra pieces. There is nothing quite like the original VW tinwear it fits better than any of the aftermarket stuff and will undoubtably give the best life to your engine. If you are able to source a complete set I would be happy to have it powder coated and fit it to your engine. Otherwise I will source the best parts currently available.
The fan in your engine is a robust part, personally I have never had one fail. The issue with using a mechanical fan is that as the fan speed increases, the power it takes to drive it increases dramatically. The power required to drive any fan is proportional to the fan speed ‘squared’, put simply if it takes 4 horsepower to drive the fan at 3000 RPM you might could be excused for thinking it would take 8 horsepower to drive it at 6000 RPM, it actually takes 16 horsepower. This energy is being transferred to the fan blades via the fan belt and alternator. There is a speed at which the fan blades will fail due to the load on then we need to make sure we aren’t any where near that speed. The ratio of the crank pulley to the alternator pulley means the fan turns at approximately 1.5 times engine speed, at 5000 RPM it is turning at 7500 RPM this should be fine for our purpose. If you are running a full race cam and running the engine at 7000 RPM the fan is doing 10500 RPM. This is the point where you should be thinking about fitting a smaller crank pulley (AKA power pulley) to reduce the speed of your engine fan. I wouldn’t recommend a power pulley for road use though.
You might be wondering why we don’t just bin the mechanical fan and replace it with an electric fan like water-cooled engines have. Firstly the radiator in a water-cooled car is cooled by airflow going through it when the vehicle is moving forward, the electric fan should only come on when the vehicle is stationary. The cooling requirements of an engine that is idling are far lower than when it is driving under load. To cool an engine at full load (3000 RPM) you really do need a 4 horsepower fan. One horsepower is equivalent to 746 Watts so four horsepower is 2984 Watts. The standard Bosch alternator fitted to our vehicles can deliver 55 amps at 14 volts, that’s 770 Watts so you would need four alternators running at full power just to drive the fan, then another to power the rest of the car. That’s going to make for a very cramped engine bay. Secondly that is a lot of stuff running at full load all of the time, it’s just a matter of time before something goes wrong. The standard fan is about as simple as automotive components get.
The subject of which oil you should put in you air-cooled engine is a big one, I am no expert in engine oil technology but I will share what I know. In recent years there have been many instances of camshafts going ‘flat’ and of cam followers failing very early in life, in some instances after just a few thousand miles. John Maher has written an interesting article on the subject and thinks he has discovered the cause of the issue. When VW designed their engine, oil contained an additive called ZDDP (Zink dialkyldithiophos-phate) the function of which is to coat sliding surfaces in an engine (like cam followers) with a friction reducing coating. Unfortunately ZDDP was found to be incompatible with modern catalytic converters so oil manufacturers have been reducing the ZDDP content in their oils, modern engines don’t have sliding surfaces within them any more. It seems ZDDP is essential to the long life of your air cooled engine especially in the first few thousand miles. Unfortunately oil manufacturers don’t want us to know what they put in their oil so it can be difficult to know which ones contain the correct additives. Millers oils market an oil they call Pistoneeze that contains ZDDP. I use their Competition Running in Oil (CRO) for the first 500 miles then switch to their Pistoneeze oil in 10W30 weight.
DPR counterweighted, 74mm stroke crankshaft.
Full weight or lightened VW flywheel please specify which you prefer.
Stage 1, 1700 lb clutch pressure plate.
Solid clutch centre plate.
Steel crank pulley machined for 36-1 trigger wheel
Full engine balance of complete rotating assembly (crank, flywheel, clutch & crank pulley).
New aluminium or magnesium engine case. Please state if you have a preference.
Quality set of 8mm cylinder head studs.
Engine case drilled for full flow oil return and oil pressure sensor.
Case clearanced as necessary and machined for extra oil flow to RH case half.
Engle 100 or 110 camshaft, please specify. Matched to bolt on cam gear.
Scat or Engle solid cam followers or Mofoco hydraulic cam followers at customer request.
Bolt up rocker shafts with modified rockers for improved lubrication.
Oil filter, bracket and all necessary pipework and fittings for oil filter installation.
26mm Shadek aluminium oil pump, plugged for full flow.
Oil pump cover incorporating oil outlet and oil pressure relief valve.
Matched set of thick wall 88mm barrels and pistons, balanced to within 1 gram.
Shims as required to give correct piston deck height.
Cylinder heads with stock sized valves, single heavy duty springs and 3/4” spark plugs, chromoly valve spring retainers and keepers. Valves machined for improved air flow.
Full set of Scat or similar tinwear modified as necessary to fit properly, powder coated in black or your choice of colour at additional cost.
Clip on valve covers just like VW intended.
All of the other bits and pieces that are necessary to assemble an engine.