well my car has a 600 CFM Holley Carb that loves to be adjusted every so often on top of a Edelbrock Performer Intake. it leads through the stock heads and cam and out a set of Hedman Headers. then the exhaust continues out a a pair of 2.5 inch pipes and through a set of 2 Chamber Flowmasters ( took off the 3 chambers for more boomy bass ) and out the dual exhaust tips behind the car. the gas and air is fired by a Pertronix Module in the stock distributor and an Accel Coil and 8.8mm wires. and the crowning achievement?? another cool sticker on the air cleaner.
When you think about it, an engine is just a big air pump. Air in -- air out. Anything you can do to help this along will enhance performance.
Things to do on the intake side - Less restrictive intake manifold, bigger or 4V carb, air cleaner, cold air ducting.
Things to do on the exhaust side - headers or HiPo exhaust manifolds, big exhaust tubing, balance tube in headpipe, less restrictive mufflers, no 'wrinkly bend' exhaust tubing, less bends in the exhaust tubing, gentler bends in exhaust.
Now we get to the engine itself -- The 'brain' of the engine is the camshaft. Most engines come with a compromise camshaft that will balance power with economy and smoothness. A more aggressive camshaft will allow more air-fuel mixture into the engine. If properly scavenged on the exhaust side, you might even draw air into the cylinders easier. This is why I prefer a split or dual pattern camshaft. They generally have more thought put into the profile to better balance out the flow characteristics of the heads.
Which brings up the topic of flow characteristics of the heads. Anything you can do to increase the flow will help. Larger valves, pocket porting, removing casting flash from the ports, smoothing out any radiuses, blending the valve to port juncture (no good having bigger valves if the port is restricted right below them!). Speaking of heads, not all chambers are created equal. some have a design that will promote a swirl effect which homogonizes the mixture in the cylinder. That's a good thing. You can have different combustion chamber volumes. The displacement of the piston will remain the same, but if you're squeezing that mixture into a smaller area, you'll get more power and torque. Same goes for dished vs flat top or popup pistons. Less combustion chamber volume = more power.
OK, you asked about power adders. Turbochargers, supercharers and nitrous oxide. Turbochagers and superchargers serve much the same function - to get more air into the engine. They just go about it in different ways. The turbo uses what normally would be wasted energy in the exhaust to spin a exhaust turbine which is connected to a intake compressing turbine rotor. The more exhaust energy, the faster the turbo will spin which in turn will force more intake air into the engine.
A positive displacement supercharger is usualy driven off a belt on the front of the engine, soit is really using some of the power of the engine to do its work.
Nitrous oxide. If you look at the molecular structure of Nitrous, it is comprised of Nitrogen and Oxygen. Oxygen is what makes things burn. More oxygen, more power. Our normal atmosphere is something like 70% Nitrogen and only about 25% oxygen.The more oxygen you can get into your engine, the better things will burn. However, since your carb is calibrated for the 'normal' air mixture, it will need more fuel to better take the benefit of the increased oxygen level. That's why you have to also add extra fuel when you run Nitrous.
Now that this windbag has gone on and on and on, you probably just wanted opinions, right?
Nitrous is a pain because you have to keep refilling that bottle. You'll run out or low at the most inopportune times!
Either form of supercharging raises the intake air temerature. That's just basic physics. You really need an intercooler to help lower the intake charge temp. Both a turbo and supercharger systems are very expen$sive. Probably $3Gs to do right. For that kind of money, I'd rather just build a better engine!
You can find parts all over. However make sure they are street legal in your part of the country. here is a number if you want to order a catalog that has a tonne of performance parts. 1800.345.4545 or go to www.jegs.com
street legal??? here in Cali all of the Classic Cougars are smog exempt now. and we have no inspections here. so HA HA HA, thats not a concern here as long as your car is 73 or older. as far as availability, performance parts are very plentiful for these cars. mechanical parts basically interchange between the Mustang and the engines are just basic Ford. nothing real exotic here.