kirby wrote:
How different is the stock spi/mpi injection set up to your aftermarket injection set up jb007?
Good question; hope I can answer it... (I'm not an expert in these things)
SPi is more like mine, only one injector is used, hence the term Single Point Injection. My TBI uses a wideband O2 sensor compared to the narrowband used by SPi & MPi. My setup is using the SU HIF44 as a throttle body, whilst the SPI/MPI have dedicated throttle bodies. Difference in airflow... don't know but I do know that a HIF44 has more than enough flow capacity for my state of tune.
The MPi is the most advanced in that it was conceived to overcome the Siamese port problem of charge robbing between the outer and inner cylinders. To achieve this they use 2 very large flow rate injectors (roughly 4 times the flow rate required) and a camshaft sensor so that they can precisely time the injection window to coincide with the opening of the inlet valves. The large injector size is required because the intake window is very small, hence a very short large charge load is required. With a 'wet manifold' system eg TBi and SPi, fuel can be left in the manifold just waiting for the next inlet event.
I have no first hand experience with the SPi or MPi systems, so I cant say what benefits they provide in practice over mine, but I know my setup has transformed my car.
Hope this has answered your question?
Edit: Sorry that last sentence sounds a bit rude.
What I meant to say was; I hope I have answered your question.
). I rebuilt the motor, gave it a mild cam (SPi grind from Steve at Brickworx, now rare I'm tipping), a set of extractors and all new sensors and a proper tune. It generally ran at about 6-6.5 litres per 100kms, and whilst I don't thrash my cars (race car excepted), I am not really light on the right foot either. It was my daily drive for 2 years, and I really miss it. Would do it again if I had the time. Good luck.
