R26 Air box

Exactly that Geoff, cut the ram pipe off then enlarge that hole, some people drill large holes across the strip at the top in that side of the box too.

 

That must have taken a while! I did what Poppaboost did and removed the foam from inside the box.

 

I’m intrigued, what benefit do these air box mods bring?

 

This is an interesting topic and idea. The same kind of mod comes up on almost all car forums where people are looking to gain a few horsepower or allow more airflow because of a remap, bigger turbo or the like.

I've been involved in and watching close the performance tuning industry for ~13 years and what strikes me odd is I have never seen an actual dynamometer comparison regarding this mod alone. It sure would be interesting.

What I have seen tough, in case of many popular cars being tuned, that the factory airboxes have huge headroom for other engine mods. For example, a Golf mk4 was once dyno tested with around 400 hp (1.8T) using the factory airbox unmodified, and when compared directly to a cone filter and trumpet intake, there was virtually no difference in power output, showing that the factory intake was coping without problem even if power output had been more than doubled.

Obviously there are big differences between makes and models of car, but it would be very interesting to hear about actual test results of this mod.

One thing to consider is the fact that depending on make and model, doing the "add holes" or "enlargening the port" mods to the airbox, this could easily end up increasing the intake air temperature, if one is ditching the cold air feed pipe from the system or introducing additional holes to it. Now then, very often I see people make the argument that small increases in intake air temperature do not matter in a turbo engine because of how the turbo heats up the air anyway plus having an intercooler etc. This argument, however, is invalid. A cold air feed will always improve performance of the whole intake/induction setup. (this is a proven fact further explaining why racing engineers will strive to build cold air feed systems on their engines whether or not they have forced induction or not)

So then, the question becomes if the added airflow capacity can overcome the effect of extra heat on the intake.

Anyone have test results on this? This would be very interesting indeed.

 

the idea of a big big hole done to the existing airbox was told by a megane tuner who has cone for the megane to sell to me at that time, so i would think he was being honest to me then.


this was something i have done to me Mi205, i couldn't really feel any difference between my home brew cold air intake slam panel and a normal slam panel. mentally feel better.

 

actually it took me about 2 hours of work, drill first then dremel

 

To build on this post to which I very much agree with what you've said... In any car, turbo or otherwise, power is gained by reducing the work the engine / turbo has to do to drag air into it. Using a turbo car as the example, the best way to do this is to have the turbo mounted at the front of the car with an inlet designed in such a way that it sits in an area of high pressure - much the same principle as why car radiators sit in a recess behind a duct (grill mouth). Take a look at some of the turbo locations in drag cars.

So obviously the issue here being that we have to run a filter which creates a pretty substantial restriction in the air intake. Two things will affect the restriction, surface area of the filter and the pore size. Larger pores = less restriction, but worse filtration. Larger surface area = less restriction, but more space required in the bay. Manufacturers of aftermarket filters spend lots of money using more complex methods to reduce the restriction ( pressure drop) but maintain filtration capabilities (multilayers, oil sprays etc).

So, assuming that your filter is the biggest air intake restriction (it will be) the intake design becomes negligible in terms of restrictions, so long as the inlet to your filter is at least the same cross-sectional area as the pipework into the turbo. Increasing the size pre-filter is going to make no difference, and something which may not have been considered is that the standard setup with a pipe leading to the airbox may actually be helping to pressurise the air on the filter inlet, thus reducing the work the turbo has to do.

It goes without saying that the colder the inlet air, the better the engine performance, but in this scenario, the filter location is not changing, nor has a separate air feed been considered.

I can understand why people drill / cut air boxes for additional noise, but would imagine that it is actually giving a negative effect (albeit pretty minimal) on performance.

 

@Geoff230F1
I'm 99% sure I've still got an already modified airbox sitting taking up space in my garage if you're interested? Saves you having to cut yours up?

 

One thing to consider also, is the shape and location of the factory inlet pipe (to the airbox). There's often a clear effort by the factory designers to manage the path and angle of the air entering the airbox. In some cases the inlet "trumpet" - which it often resembles - is made to continue some way inside the airbox and the end part is then angled so that the middle of the filter panel is the closest to where the trumpet ends. That way the shortest distance for the air to travel from the carefully shaped trumpet is to the middle of the filter, so there can be more uniform division of airflow to the filter panel - and the straight path through the filter into the turbo inlet pipe or intake manifold on a N/A motor is then the shortest one possible.

About the shape of the inlet trumpet, I use that word because we often see the bell-shape (or trumpet) of some sort where the air duct begins at the front of the car. The principle is the same as you see on throttle bodies or performance carburettors when no filters are present - the trumpet shape can help increase the airflow beyond what could normally be achieved by the pipe diameter alone. In the other end of the pipe, some shapes can also be seen. In case of the Renault airbox shown in the picture above, we clearly see the inlet pipe ending has been built to have smooth and round transitions to the airbox, again, to help the airflow and its wanted direction and division.

The point made above by james.moseley is very true; if the turbo inlet pipe has a certain diameter, then having a cold air feed into the air box of a larger diameter, it would not increase total air flow by itself. What it possibly could do though, is create a ram-air effect IF you had a large and well placed "funnel" of the trumpet shape in the front of the car, then that connected into the cold air feed and have it all sealed, then a ram-air effect could be achieved by "overpressuring" the airbox. But I've not seen actual comparisons in dyno tests of this either.

 

Yes, the foam works as sound deadening, but thing is Renault accounted for the foam when designing the airbox. So the shapes and sizes for the pipework, the size and angle of the filter panel - and that foam - all come together in how the complete airbox was designed to work. So if you'd really want to optimize everything in a big way, you'd have to test the intake with and without the foam. Might well be you'd find there to be no difference in performance. Might be you'd get a modest gain. But the problem with mods like this is always that without proper testing none of us really know the effects. When bigger changes are made to an intake system, for example, then you might gain some top end power, but lose mid range torque at the same time.

One thing that's easy enough to do is to test whether or not the intake system needs any improvement in any given car. On a turbo engine like your Megane this is simple. You can measure the negative pressure present between the air filter and the turbo compressor inlet at peak load. If there's significant negative pressure present, then your filter or your intake system is creating too much restriction for the engine to perform at 100% capacity. Unfortunately I don't have the tables at hand where the limits of said negative pressure are laid down, but I'll see if I can find that old book somewhere that had these great guideline values.

In any case, it's highly unlikely the stock intake system is causing much resistance on a stock engine, and even with a normal remap it should be very adequate. And like others said before, it's the filter, not the intake system itself that will be causing the greatest resistance when the limit of the stock system is reached in a more highly tuned engine.

I could be wrong, but my experience would indicate that an improved ram air function feeding into the stock air box - well sealed - would be the most likely way you could try to improve the intake system on your car. But is it worth the hassle? We'll never know without a dyno test before and after

 

I would imagine you’re right about the foam, it is just there for sound deadening and won’t have any tangible effect on how the airbox performs.

I run a stock intake system and stock airbox, but the car is only stage 1 mapped. I have no need for anything more than that!


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I replaced mine with K&N air filter, noticed it possibly revs a bit quicker pulls slightly harder at the top of the Rev range.

 

My Engine is standard, showed 269bhp on Dyno, that was with the standard air filter.

 

Modified my airbox but that was really just for improved sound if I am honest. Didn't notice any drop in performance. Now have an induction kit and properfekt recirc valve but again, mostly for noise and with the battery now in the boot, to make access easier to things like the fuse box.