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Forgive me if this is a silly question, but what are the disadvantages to using semi-sequential injection (haltech elite1500 on a 6cyl) over sequential?
I understand how semi-sequential works, but does the batch that is firing on the closed valve (assuming correct injection timing) have any real world negative effects of performance?
Is the marginally more precise fuel timing worth it on an engine that is likely not that highly stressed, given that as RPM and load increases, there is likely some fuel being squirted on a closed valve even when using sequential injection (as I understand it anyway), going to cause problems? I also understand that the injection phase starts earlier to offset this, but does it actually make 'that' much of a difference?
This is not a max effort engine. It will see mostly street driving with the occasional trip to the drag strip (trapping somewhere in the ballpark of 135-140mph at 1100kg).
Don't worry about it.
Semi, or batch, will give you the same performance.
I insist on "fully sequential" only when a vehicle has to pass an emission drive cycle (homologation procedure), to quench out the last bits of unburned carbon oxyde.
As DynoDom said, sequential is mostly just a fuel saving. You MIGHT notice a slight drop in throttle response but probably not. The other main benefit of sequential is the more precise control over timing and duration, again this is real fine tuning that most engines won't have done anyway.
As it isn't a full race engine, I shouldn't worry about it. This like getting the cam profile/timing and intake/exhaust designs right will make far more difference.