Modify it in the constants.ini file but dont go over 450......you can also adjust the engine output like my "my_super_01"
[Engine
nickname = my_super_01
ids_name = 263697
ids_info = 264697
volume = 0.000000
mass = 10
max_force = 500000
linear_drag = 333.333
power_usage = 0
reverse_fraction = 0.200000
flame_effect = gf_rh_smallengine03_fire
trail_effect = gf_rh_smallengine03_trail
trail_effect_player = gf_rh_smallengine03_playtrail
cruise_charge_time = .5
cruise_power_usage = 5
character_start_sound = engine_rh_fighter_start
character_loop_sound = engine_rh_fighter_loop
character_pitch_range = -50, 25
rumble_sound = rumble_h_fighter
rumble_atten_range = -5, 0
rumble_pitch_range = -25, 25
engine_kill_sound = engine_rh_fighter_kill
cruise_start_sound = engine_rh_cruise_start
cruise_loop_sound = engine_rh_cruise_loop
cruise_stop_sound = engine_rh_cruise_stop
cruise_disrupt_sound = cruise_disrupt
cruise_backfire_sound = cruise_backfire
indestructible = true
outside_cone_attenuation = -3
inside_sound_cone = 60
outside_sound_cone = 180

in the engine_equip.ini .....My ships max flight speed is 2500.

"Live Fast Die Young, For this is the only way a Freelance Merc. Can Survive the universe."

*HSDS*VINDICATOR Nomad Hunter

constants ini edited

[Constants
COLLISION_DAMAGE_FACTOR = 0.500000
MUSIC_CROSS_FADE_DELAY = 10.000000
MUZZLE_CONE_ANGLE = 40
PLAYER_COLLISION_GROUP_HIT_PTS_SCALE = 3
PLAYER_ATTACHED_EQUIP_HIT_PTS_SCALE = 5
MAX_PLAYER_AMMO = 9999 ;add this line set this to what you want

[EngineEquipConsts
CRUISE_DISRUPT_TIME = 5 ;sets time to reach cruising speed lower is faster
MAX_DELTA_FX_THROTTLE = 0.250000
THROTTLE_STEADY_TIME = 0.500000
THROTTLE_ATTEN_MOD_RANGE = 8.000000
DELTA_THROTTLE_ATTEN_MOD_CHANGING = 8.000000
DELTA_THROTTLE_ATTEN_MOD_STEADY = -1.000000
CRUISE_STEADY_TIME = 2.000000
DELTA_CRUISE_ATTEN_MOD_STEADY = -1.000000
CRUISE_ATTEN_MOD_RANGE = 8.000000
CRUISING_SPEED = 2500 ;add this line set = to what you want

cruising speed is set on this line crusing _speed =

if you want to set CRUISING_SPEED above 990, eg 2000, you have to add another line, which would be ANOM_LIMITS_MAX_VELOCITY = 2000 under the [PhySysConsts section.