Throttle body conversion- background information
Introduction: I have been
contemplating once again the switch to fuel injection. Much as the twin 40s give the car 'character', throttle bodies still give a nice induction noise, and you lose all of the annoyances of carbs: getting the idle mixtures set up the same on all 4 cylinders, grumpiness in cold weather, occasional popping and banging, not so great fuel consumption (although the 30mpg that I get on a regular basis is not tooooo bad...), the list goes on...
750 & 1000 from 2000-2003
600 from 2000-2003
Post-2003 600, 750 & 1000
2 - Re-use a DCOE manifold, with adapter stubs to suit. The GSXR TBs do originally come with stubs that will work, but the bolts that hold them to the head on the bike are prone to seizing, and hence they are difficult to get hold of second hand. New from a Suzuki dealer they are about £60 a set. Alternatively, you can get equivalents made:
3 - Adapt the manifold from the original EFI installation. This will vary for different engines, but normally involves chopping down the original manifold, and then either connecting the TBs direct, or welding on some additional tubes, in either case using hose to mount the TBs. In many cases you may be able to re-use the original injector location, which is normally positioned to inject onto the back of the inlet valve(s), which saves the need to use the bike injectors and associated costs with changing the fuel rail.
4 - Use the stub manifold from a Ford Focus ST170. This is obviously only appropriate to Zetec engines, and is similar to option 3 in that you can retain the Ford injectors and fuel rail, with the difference being that you don't need to cut the manifold down- it is in 2 parts already. Discard the plenum section and use the Ford rubber hoses to connect to the TBs. The TBs will still need re-spacing, and the Ford fuel rail needs modifying to add a return line. The injector locations on the TBs can be blocked. However, in my case , the downwards slope of the engine cover would clash with the TBs sitting at an upwards angle, so this method was not an option for me.
I have decided to give option 3 a try, with the theory being that I can switch to option 1 at a later date if I'm not happy with the end result. The original Ford Zetec manifold is a little awkward in that there is a 'sandwich plate' mounted to the head which contains the injector ports, and then a separate cast manifold/plenum. I considered whether I could mount the TBs direct to the sandwich plate, but this looked to be difficult. So, I got the angle grinder out and chopped the manifold roughly in 2, separating the plenum from the inlet runners. With the plenum now out of the way, I chopped back the runners further so that I had a 20mm stub protruding from the manifold face. The external webbing had to be cut away to allow a hose to be slid on to the stubs.