why do you need more lsa for a fuel injected engine? and what are the perks of a lower lsa?

 

Do you possibly mean "why do you need more LSA for a forced induction engine?". With a blower, or nitrous, you want to minimize overlap to prevent the charge from blowing through the open exhaust valve, while allowing you to increase the exhuast duration to handle the larger volume of gasses generated by the nitrous or boost.

A wider LSA will generate more idle vacuum, and generate less emissions, so you will often find wider LSA's in newer, emissions controlled engines, which also happen to have fuel injection. In very general terms, reducing the LSA will raise the peak power level and rpm.