It all depends on how much you want.
engine programmer can be a good bang for the buck
cold air intake
under drive pullies or replacing clutch fan with a electric fan
tri-y or full length 4 into 1, shorties are a waste
cat back exhaust, but newer cars don't pick up as much as older cars
from there on it gets expensive, involved....
turboes
superchargers
cam/intake/rr
ported heads/hi-po heads
stroker kits
Alf Engen was born in 1909.
Alf Engen died in 1997.
Whitney Engen was born in 1987.
Engen brothers died in 1997.
Engen brothers was born in 1909.
Corey Engen was born in 1916.
Corey Engen died in 2006.
Asbjørn Engen died in 1985.
Stig Engen was born in 1959.
Svein Engen was born in 1953.
Hans Engen was born in 1912.
Sverre Engen was born in 1911.