i know the 87's hp is about 140. some will say 120 but i think that is only the 318 in cars that is 120 and the trucks are about 140. When they went to TBI the HP went up and the torque went down slightly. So 150 hp sounds right but i think the torque was a tad higher. In 1991 the hp on a 318 jumped up to 175. Not sure why though.
Now adding headers your hp and torque would be higher. Every engine is different on how much they add. but i would say 10 hp and 10 ft-lbs of torque is about right for the 318's mild state of tune.
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