Chapter 3 "Rozzer is having a problem with his differential" Part 3
Once I had the final package solution, I had to change that into a viable design. I will show you the steps now, but this actually went on concurrently with the next few chapter(s) where I will cover casting and machining the head. (I have no idea how many chapters there will be, I’m making this up as I go along.)
The manifold, as shown above, is a single piece. How could I make this? If it is too hard to make do I split it into an assembly and if so, how many parts and where do I make the split. Finally, how do I make all the separate parts.
Looking at a single part, well I could cast it but that’s one big casting and once made leaves no room for modification etc.. So, no not a casting. What about a fabrication? Well it could made from Aluminium but as I can’t weld or fabricate aluminium (my steel welding ain’t so good either!) that would be expensive but would at least be modifiable. FRP is an option, but would take a lot of work, I have never made anything that large before. So, a single piece seemed to be out of the question.
The most common way to split the system is into a plenum chamber and inlet tracts so this is the direction I chose. I decided on a split line between the two parts, keeping all of the plenum volume in one part. Much CAD and prototyping helped me to get a shape for the plenum chamber: As a general rule the plenum chamber should be about the same volume as the engine displacement for a normally aspirated 4 stroke engine. This is actually quite small and a hard target to achieve!
Initially I was going to make 4 short cast inlets Joined by a laser cut backplate. 4 velocity stacks would smooth the airflow. However, it became apparent that a single casting would be cheaper and easier to make so that was the final direction I took. One of the drivers for the multi part inlet was to aid assembly and plug changes however during the development I realised that the easiest way to get to the plugs was to remove the complete inlet assembly rather than disassembly parts of it! Yes, it’s a bit tricky to do but with all the limitations I had to work around some compromises seemed inevitable. The way I have mitigated this is to use Iridium plugs that last about 100,000 km.! I am thinking I don’t mind removing the manifold every 10 years to change the plugs!
The plenum is made from GRP; I made a 3D print of the inside of the plenum, I then overlaid it woven glass mat before adding 2 steel reinforced flanges and then a final few layers of woven mat. Once finished the 3D print was broken up and removed.
Attachment:
001.jpg
Attachment:
002.jpg
Finally, I was able to find places for the coil pack and fuel pressure regulator. These look a bit snug to the brake master cylinder but have sufficient clearance to ensure that they will not contact due to engine movement
On the dry build images there is a grey bracket that runs across the front of the engine under the plenum. There is a pin on this which locates onto the plenum. The function of this is to support the inlet system that is cantilevered off the head. While the weight is not too great; during driving the vibrations and potential resonations could cause a failure, especially of the GRP. This pin that locates onto a rubber bushed hole will absorb these. You will see this sort of design on a number of production cars. I have also found that it makes assembling the manifold a lot easier, once located onto the pin the manifold stays put while you put the 8 bolts in!
Enough I hear you cry, I will leave the chapter there!!!