[garrett]

i have a 1978 mustang mach 1. the guy that owned it before me had the engine stroked to a 347. it has a comp cam pro street, weind intake, a holley 4barrall double pumper 600cfm carb, original heads that have been ported and polished, hydrolic lifters, original exahust manifolds, and a built c-4 tranny. i have only started the motor once out of the car and it sounds way strong but i am curious how much power to expect from it any help or rough guess

 

[chesmu]

Maybe around 260-280ish. The stock heads really sucked back then, and they are a bottleneck in this application.

 

[Avigdor]

well, without any specs on the cam it'll be difficult to give any kind of definitive answer. I am curious as to why the stock heads are being used as well as the exhaust manifolds. Both pieces are very restrictive; even when ported, compared to aftermarket parts. If I had to guess...290-320 MAYBE.

 

[jakome]

Power depends on a lot of different factors.
I'd say at least 350 HP not knowing about your engine except what you posted.
My '347' type engine makes well over 500HP on a carb without N2O or any type supercharger......