[ehall]

The three most noticeable changes I've made to my 4.1 are advanced timing, Borla muffler, and Accel 8.8 wires (bought to fix a buzz but improved line response surprisingly). At some point after I finish working on my Jeep I'm planning to swap a 4.9 block under my 4.1 TBI intake.

Performance tuning of a four-stroke engine is pretty much universal. The first down stroke has the cylinder suck air and fuel into the combustion chamber, the next upstroke compresses it, then the spark ignites the mixture and pushes the cylinder down, then the next upstroke expunges the exhaust. Only one of these strokes produce power, while the other three consume power.

Most bolt-on mods simply aim to reduce the amount of power that is consumed as waste, and do not actually produce a better power stroke. IE, better airflow in and out of the engine results in less energy being consumed on sucking air into the chamber and expunging gasses exhaust out, which in turn allows a larger remainder of the existing power stroke that can then be used by the drivetrain. High flow is key to this, but don't confuse "bigger" with "better" on exhaust--you need to manage back-pressure in the exhaust for scavenging to work right and you will have to use a size that is appropriate for maximum torque at a specific RPM band.

You can also do some simple things to improve your power stroke. IE, better ignition parts will produce a more consistent explosion which yields a less ragged power stroke, while an earlier ignition will produce a longer power stroke that produces more power.

You can also do some things to the drivetrain, such as regearing for lower torque, although this will negatively restrict top-end capability.

In the end there is no replacement for displacement, and if you really want to burn the rubber off your wheels you will need much more combustion.