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Throttle Body Injections


Perfect Power Articles.


A throttle body injection (single-point, SP) uses one (or more) injector at a central point before the gas is getting to the cylinders via the inlet manifold. A multi-point (MP) injection system uses one injector per cylinder; the injector is located at the end of the inlet manifold or the head.


The prime difference between the two systems is:

The SP system has a small hesitation between gear changes. This is the result of the manifold going "dry" when the throttle is taken back. This hesitation can be eliminated with a "throttle damper": A device which doesn't allow the throttle to close completely during gear changes.


The SP system is much cheaper, because it uses only one or two injectors.


The SP system can't compensate for difference in gas flow to the individual cylinders. The MP method, driven by a sequential injection system (such as XMS), can compensate for gas flow differences. Each cylinder can be tuned separately. Monitoring the exhaust gas temperature on all cylinders, and then tuning the fuel to achieve equal temperatures do this. The tuning process is manual, and only warranted for high performance engines.


A controversial issue: The SP system is supposed to give better performance, because the fuel has more time to mix with the air in the long runners. We have experienced better Hydro Carbon (HC) on SP systems.