Saturday, 21 April 2012

SECRETS OF CYLINDER HEADS

Cylinder Heads



              One of the most confusing parts of learning about the tuning of the Type 4 is the cylinder head. In general, most Type 4 cylinder heads are interchangible with most other cylinder heads. This part of the tour you will learn about the different cylinder heads (or commonly referred to as just 'heads') and what makes each model unique.

                          All Type 4 heads feature longer valves than the Type 1, along with longer valve springs. All of these heads feature dual intake ports, in a similar location to the Type 1. The exhaust ports exit through the bottom of the head and the exhaust manifolds travels between the pushrod tubes.
                      Inside the rocker area, you'll notice that there are four studs per head. The rocker assemblies are paired, one assembly for one cylinder. Each stud holds that side of the rocker assembly together.
Well, let's get started with the heads from the . . . . .
 





                     The first cylinder head was basically the foundation for all of the forthcoming engines. What makes the 1.7 head unique is the 39.3mm intake valves, the 33mm exhaust valves, small intake ports, and smaller cylinder bore opening. The small intake ports can limit performance of any engine built with these heads, but simple portwork can fix that. The small cylinder bore openings can create sealing issues, especially with higher than stock compression ratios.
               Flycutting the heads and using later model cylinders (and pistons) from a 1.8 can give you 100cc of displacement and better sealing.
                         The picture on the bottom is detailed enough that you can see the part number that is stamped into the head. This is the easiest way to quickly identify the heads. Armed with this number, you can than look up the number on "Cylinder head" .




The top left picture is of the bottom of the 1.7 cylinder head. You can see the unique position of the exhaust ports and how they are buried in amongst the cooling fins. The same description could be said of the spark plugs on the top of the head. In the middle photo you can see that the spark is angled towards the middle of the cylinders.
In the combustion chamber we see the unique shape of the 1.7 head and the 39.3x33 valves. Compare the combustion chamber shape with the chambers from the other heads; they are all similiar, but each model is unique. It's been said that some tuners like the 1.7 heads for the combustion chamber size and they report that they are stronger, but realize this is only heresay.





A few improvements were incorporated into the 1.8 cylinder head. These improvements included larger intake ports, larger valve combination ( 41mm intake and 34mm exhaust ), larger cylinder bore (which would stay this size for the remainder of the Type 4 engine's existance), and a revised combustion chamber shape.




                                 This particular 1.8 head came from a '74 Bus (AW case code) and featured air injection for emissions control. On the top left picture, you see a large hole immediately adjacent to the left most intake stud. That hole is for injecting air in to the intake ports. If this head is to be used without this injector, this hole must be sealed somehow.
                               The middle photo shows that besides the enlarged intake ports, the heads from this angle are essentially the same. The exhaust ports didn't change either, as the right photo showcases.





                                 These shots show us the combustion chambers and the 41x34 valves. Compare these combustion chambers with the 1.7s and you'll the rather small changes in shape.
                              Also not as readily apparent from these pictures is the fact that the cylinder opening of the head has been increased. The top of the 93mm cylinder was increased in diameter, so the new head was changed appropriately. This increased the sealing of the cylinders to the head and solved the intake leak problem with the 1.7.

914/912E 2.0





            When Porsche introduced the 2.0L Type 4 engine in 1973, it featured a unique head design that was only used on 2.0 914/4s and the 1976 912E. This cylinder head features a unique spark plug location, the largest valve combination (42mm intake, 36mm exhaust), and a unique combustion chamber shape.

         The quickest and easiest way to distinguish a 914/912E 2.0 head is by the three intake manifold studs; all other Type 4 heads had 4 intake studs. These studs are readily visible in both of these pictures. Another item to note is the angle of the spark plug and how it differs from the other Type 4 heads.





                    Here we see the largest valve combination from either VW or Porsche. It's generally been accepted that the Porsche 2.0 head flows the best and makes the best power of all of the Type 4 heads. It's also been reported that this head suffers from cracking in the exhaust ports.
                     This head commands a higher sale value on the street, so before paying a lot of money for a set, make sure that you check the exhaust ports for cracking. If cracking exists, it can be fixed, but be aware of this extra cost and use it to bargain the price down.


Bus 2.0





                        The Bus 2.0 is essentially the same head as the 1.8 head. The Bus 2.0 head has the same intake ports and spark plug location. The reason that most people don't use the Bus 2.0 heads is because they have lived a long and tough life, pushing around a large, unaerodynamic bread box, with drivers who generally drive at too low a rpm range. Careful inspection of a set of these can yield a good set of heads for a mild driver.





                      This is the last cylinder head to utilize this style of exhaust port. Since VW used the same port design through most of the Type 4 engine life, exhaust systems and cylinder heads are interchangible. The picture on the right shows the details of the port. You can see the sharp bend and how it's buried into the head.





                        These shots illustrate the smallest valve combination in the Type 4 series, 37.5mm intake and 33mm exhaust. Once again, the combustion chamber was changed in an effort to make the most power and lowest emissions for use in a Bus. You'll notice that the spark plug almost points straight down, in between the valves.


Vanagon 2.0





                   The "Vanagon 2.0" head, called this because it was used almost exclusively on the 80-83 Vanagons. It was also used on the '79 Transporter, but most still refer to it as the Vanagon head. The Vanagon head is basically identical to the Bus 2.0 head. The noticable difference are the exhaust ports.





                      Compare these photos with the ones of the Bus 2.0 combustion chambers and you'll see for the first time VW did not change the chamber shape. It could be because they didn't change the valves and that the engine was pretty much identical.
 
 








                      This photo basically sums up the difference in the Vanagon 2.0 head and all the rest. The exhaust port design was changed with the '79 Transporter to this type of design. It was this design change that makes the Vanagon head different the from the earlier Bus 2.0.

                       One reason for this change in exhaust port design was for installing exhaust manifolds. The earlier ports utiliized a copper ring that had to sit on top of the manifold, whereas this new design used a conventional gasket that didn't slip off when you mated the two pieces.

                           Because of the exhaust port change, earlier exhaust systems can not be retrofitted to this head. There are some aftermarket exhausts for this head, but the selection is very limited. Hopefully as the Type 4 gains popularity, more exhausts will be made with these ports in mind.


Type 1 1600cc dual port








                        For those of you that are not familiar with the Type 1 1600cc cylinder head, I've included a pictures of a head I had laying around. This particular head was originally off of a Type 3 1600cc engine but are basically identical to those used on the Bug and the current production aftermarket units. The dual port heads all feature 35.5mm x 32mm valves, exhaust ports that exit to the front and the rear of the car and closely placed intake ports.

                       This series of heads has a problem with cracking between the valves or between valve and spark plug hole. The closely spaced intake ports makes increasing the intake port difficult, as care has to be taken to not make the wall between the ports too thin. The intake ports also feature a sharp bend from the port opening to the valve seat. This bend can be straightened a bit by porting the intake port closer to the exhaust port.

I'd like to thank Phillip Sparta (1.7), Steven Jenkinson(914/912E 2.0), Matthew Bulley(Vanagon 2.0), and everyone else who made photographic contributions. All lot of people were generous enough to contribute their time to take some great photos to share with everyone. Thanks guys!!