Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_66 ( specific_impulse__s_ INTEGER, sfc_in_lb__lbf·h_ VARCHAR, effective_exhaust_velocity__m_s_ VARCHAR )

### Question ###
what is the average specific impulse for engines that have a SFC in lb/(lbf h) of 7.95, and a Effective exhaust velocity (m/s) larger than 4,423

### Accurate SQL ###

SELECT AVG(specific_impulse__s_) FROM table_name_66 WHERE sfc_in_lb__lbf·h_ = 7.95 AND effective_exhaust_velocity__m_s_ > 4 OFFSET 423