could happen as it looks like its a 1/8th track
the si, also known to many as the torqueless wonder, does not make its horsepower to well into the rpms, it makes 160 hp at 7600 rpm
with a bad launch a b16 takes a while to get up to speed

also at 70 mph the si's gearing means its in 3rd gear
with the ex cant it still be in 70, or is the gearing shorter?