This is plagarised from the Clio 16v tuning guide on the main site:
The first item on most modders checklist is the air filter. On a Clio 16v, as on most cars, the actual filter is inside an airbox. The airbox is attached to the inlet manifold via the throttle body, and when you press the accelerator, the throttle plate opens wide, sucking air into the manifold and from there into the engine. But where does the airbox get its air from? Well this comes from a plastic pipe that leads down to the nearside front of the engine bay, at the bottom. The air is sucked from a space behind the foglight which is relatively cold and remote from the engine block.
So thats the layout, why would you want to change it? Well it depends on what you want from your car. The standard airbox and filter work pretty well but its construction means that it doesnt flow as much air in as the engine can actually handle, therefore restricting potential power. So why not get rid of the airbox/filter and put in something less restrictive? Well this is exactly the principle behind an induction kit.
An induction kit comprises a filter body, usually in the shape of a truncated cone, which is a complete unit - the filter media (generally pleated cotton or foam) is a permanent part of the body (usually some combination of plastic, rubber or metal). Therefore an induction kit doesnt need replacing every service; it just needs removing and cleaning occasionally. The other part of the kit is some form of ducting to get cold air to the cone.
The idea of an induction kit is to increase airflow and a secondary effect is that it makes an induction roar, which basically happens because you no longer have the airbox acting as a silencer. An induction kit can increase horsepower (not by a lot - ignore any claims over 2 or 3 bhp for an induction kit on its own) because it is capable of flowing as much air as the engine could ever require, especially when the engine is highly tuned. But it is also highly likely that you will lose power if you do a lot of driving in town or at low speed. The reason for this is that it is not just the amount of air going into the engine that matters, but also the density of it.
When the engine sucks in air, it uses the oxygen to start combustion. Cold air is denser, thus contains more oxygen. Hot air contains less. So even though an induction kit may flow a lot more air than the original airbox, if this is hot air that has been circulating around the engine bay (caused by radiant heat from the exhaust manifold, engine block, cylinder head, radiator or coolant pipes), you are pretty likely to be supplying the engine less oxygen than it is expecting! As you will know, a Clio 16v gets very hot under the bonnet even after a 10 minute run, and this is the problem induction kit manufacturers have not addressed. The throttle body is very close to the main sources of heat on a 16v engine and the airbox bolts straight onto it, as does any induction kit. The airbox acts as a heatshield on the standard car, and sucks fairly cold air from a void in the bumper.
An induction kit however, will suck whatever sort of air it can find into the inlet manifold, whether hot or cold. Unless you can give it any reason to pull in cold air, it will suck the hot air that is all around it, under the bonnet. To get cold air flowing over the filter which will also help to push away any hot air in the vicinity, it is not enough simply to use the orignial airbox duct as a cold air channel. There is no air being forced into that cold void behind the foglight, so there is no reason for any cold air to come up the pipe and onto the filter. Even worse is leaving the induction cone with no pipe at all. This is guaranteed to lose you power in every situation.
A K&N induction kit comes with a measly pipe that you have to poke through the radiator surround, which allegedly ducts the cold air to the filter. It may well do, but the cold flow through this pipe is insignificant compared to the hot air all around the filter and thus only at high speed does this system even have a chance of working. Even then hot air will be sucked in from the opposite side of the cone. Green and JR induction kits work in exactly the same way as K&N, they just look a bit different. Pipercross and Ramair make foam filters which use the same principle as the rest: point an air pipe roughly in the direction of the cone and hope for the best - maybe the induction roar will convince you that your car is more powerful!
The reason why none of these induction kits do the job they should be doing is that on a Clio 16v they need heatshielding and they need a big bore pipe which will direct pressurised cold air all around and close to the filter body, enough pressure to blow away any hot air under the bonnet. If youve got this far you might be wondering why anyone ever gets rid of the airbox in the first place - it is the perfect tool for the job, keeping heat out and not requiring a pressurised air supply because it is a sealed system.
Anyway to get to the point, there are three options I recommend for your Clio 16v, one of which is obviously stupid - can you spot it?
Get a Hill Power Ramair induction kit, fit it and connect up the bottom pipe to the original airbox connection, then knock out the blanking plate next to the foglight to allow air to be rammed in at almost any speed. Behind this new hole, the cold air has nowhere to go except up the pipe, into the bottom of the heatshield bucket and then around the entire body of the filter. Any cold air which is not actually sucked into the filter body is ducted up and out, thus keeping any surrounding hot air at bay. Even at standstill or low speed, the fact that heat rises means that it is not easy for any stray hot air to get down into the bucket. Results = a few extra bhp at speed, no significant losses at standstill or in slow traffic, loud induction roar, no filter to replace at each service.
Keep your original airbox, take out the Renault filter media and stick an aftermarket filter element in there. I dont think it really matters what brand you choose. Pipercross, Ramair, K&N etc, they all do the same job. Results = It will flow air better than the original and will not need replacing at each service, noise level will remain the same and power should be slightly up at any speed.
Buy a flashy induction kit, find that your car actually feels slower, then go to all the trouble of fabricating a custom heatshield and through-the-bumper ducting, only to find that it still isnt keeping the heat out as well as youd like. Althernatively leave the kit as standard and find that the cone (not Pipercross) may melt on hot days in traffic. Results = Very slightly more power at speed, power losses at slow to medium speed, loud induction roar, no filter to replace at each service.
With all the facts in front of you, you can see which is the stupid option. I dont believe that modders are stupid, I just think that many magazines, tuners and filter manufacturers perpertuate the idea of and induction kit as an essential first step without considering all the points I have raised here (more likely is that they realise all of this but keeping quiet sells more induction kits!) That is why a large proportion of modded Clios have gone for option 3!
Dont fall into this trap - I myself started on option 3, ditched my melted K&N for option 1, and have had no trouble since, and respectable power gains - I personally recommend the Hill Power kit (see picture on left) but make sure you open the duct in the bumper as well! If I just used my Clio around town I would definitely go for option 2, it is the best for reliable power. By the way, drilling holes in your airbox to allegedly give more power and induction roar is one of the most ridiculous things I have ever heard. All this does is mess up the one advantage that an airbox does have, ie. it is sealed and draws cold air in. The box itself is not the restriction to airflow, it is the filter media inside it that is restrictive, but you wouldnt put holes in the filter media, would you?
For those of you still not convinced, if you simply must fit a standard induction kit to your Clio and are going to ignore my advice, at least get a Pipercross - it looks decent and is well built - it wont melt, you get a lot more for your money... : )
