Originally Posted by plastic penguin
The only way to gain an appreciable improvement is by fitting a bigger engine or, if the car is suitable, have a turbo unit fitted.
I look at performance filters in the same way as having the ECU remapped: If the engine size is below 2 ltr, you're probably wasting money.
Agree some what with what you are saying. But not about the engine size.
Thing is an engine to make more power needs as much air coming into and leaving the engine as fast as possible. No if's no but's no coconuts!
If the ratio ideally is 14.7:1 for an optimized fuel burn on a petrol you need as much air in each cylinder fill.
This is why remapping Turbo car's works far better. You can just increase the turbo spool. Thus getting the engine more air and thus more power.
Similar with diesels but they just chuck more fuel in and the ECU does the rest.
The only way to get increased power from a Naturally Aspirated engine is to physically change items in said engine :-
Camshafts (More aggressive)
Better / Larger intake (getting more air in)
Better / Cleaner Exhaust
No Cat Converters (Restrictions)
Lowering Inertia weight of parts (Crank / Fly Wheel / Pulleys / Valves)
Using Thinner weight oil (Less drag)
Improved intake (Air again)
Increasing Rev's. The higher the Revs the more air is being sucked through the engine (Generally)
Air intakes can help. It removes a restriction. How good they are depends on the original design over stock. How its positioned. How many bends. Pipe diameter.
It might increase peak power but might reduce it else where.
All tuning is a trade off.