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Originally Posted by mustangiighia  The best and easiest thing to do is get some better flowing heads. The stock heads suck. Then get a new better flowing intake manifold and carb. Just look in summit or jegs or any site that sells parts for a Ford 302 and you'll find what you need. |
The Mustang II's stock heads are fine for 200-250hp.
The problem is the stock pistons.
If you look in the High Performance Ford Parts Interchange (a book you can buy at most Autozone and Barnes and Noble stores), you'll see that the Ford heads from 1977-1995 were basically the same. Very small differences in overall design, but had the same sized ports, valves, and combustion chambers.
The stock pistons in a Mustang II, however, are deeply dished for low compression, where as the stock 5.0 HO pistons were flat-tops with valve relieves cut into them. That, and the more aggressive camshaft, are where the 5.0HO gets its power from.
The easiest bolt on power for a Mustang II is a 4-bbl carb and intake, followed by headers and exhaust. That'll put you in the 150-200hp range depending on choices in parts, condition of your engine, and other factors such as timing, what kind of fuel, what altitude, whether you're running full accessories, and what kind of fan you're running.
Rebuilding the bottom end with a more aggressive cam and flat-top pistons puts you in the 200-240hp range, again depending on parts selection and other factors.
For 300hp, you will need to replace the stock heads, but if you're doing your buildup gradually, they're the last thing you'll need to replace.
A 302 with a moderate cam, flat-top pistons, GT40 or better heads, an Edelbrock Performer RPM or Weiand Stealth intake, a decent pair of headers, and a 2 1/2" performance exhaust and a good ignition system should see roughly 275-300hp at the flywheel, give or take.
Car Craft Magazine got 400hp out of a stock 5.0HO short block with AFR 185 heads, a 4-bbl intake, 625cfm Demon carb, and tri-Y headers on it. That engine even had the stock cam still in it. (though the valvetrain was upgraded with 1.7 rockers and a few other pieces).
1978 Mustang2 Ghia. Looking for more power. 
