V40 Airbox

[Daf-T]

I have a 1.8i V40 (non-turbo, non-GDi). On this web-site, under Induction Tuning, it mentions that on smaller engines, replacing the airbox for a competition filter or Cold Air Induction Kit can actually LOOSE you power.

Why is this?

Why does this only happen to smaller engines?

ChipTuning (Volvo tuners) also told me that replacing the airbox will loose me power, but they won't reply to my enquiries about WHY this is the case.

I have modified a scrap airbox base, taking out the hot/cold air flap and replacing the induction 'flute' tip with a larger bore duct (in both cases to reduce any restrictions in the airflow). In the light of the potential power losses mentioned previously, I can't help feeling that I'm again loosing power!

Can someone tell me why / how smaller engines loose power when they have their OEM airbox replaced, when larger ones positively benefit from it.

Thank you, fine Volvo Peeps.

 

[obi_waynne]

Hi Daf-T nice to have you along. We seem to be getting quite popular with Volvo owners now. This is one of those urban legends that everyone repeats and no-one really knows or bothers to find out why. Rather than give a really techy answer here is my take:-

The thing you notice the most when driving is Torque, just as losing back pressure will rob you of low down Torque so will freeing up the air intake. This is really noticable on smaller engines which do not have much low down torque to start with. It's worth noting that all engines will get more top end power from an induction kit in the upper part of the rev range.

I'd be interested if this idea works for you :- try fitting a butterfly flap to the intake pipe to create a restriction at low revs and then at full revs the flap will be forced fully open :twisted: this might be the thing that gives you the best of both worlds! There can also be a fuel starvation issue coming in to play as well so it is worth trying larger injectors if you are starting to run lean - try an emissions test and see if it starts to run lean when the airbox is removed.

The makers also spend millions on airbox design - the total length of the induction line also has an effect on power. The induction kits that suck in warm air from the bonnet also lose a lot of power.

 

[only_happy]

I think the problem you would face is air velocity.

The engine sucks in 'x cu ft of air per minute. a small pipe will cause too much resistance and not allow enough air to enter the engine, but the air that is passing through will be travelling very fast. as you increase the bore diameter of the pipe the amount of air that can pass though is increased, until the engine is sucking as much as it can in. at that optimum point if you increase the bore diameter again, instead of more air passing through, the same amount does but at a slower speed, therefore not as much air rushes in to the cylinders due to the slower velocity - reducing your power.

out of all my Volvo's -
440 1.7 carb
440 turbo 1.7 inj
480 1.7inj.
4601.8 inj.
240 2.0 inj
760 2.8 v6
and my current s40 2.0 turbo

all i've ever been advised (by pipercross and K&N) is to change the panel filter. the air boxes already have a cold air intake (on the 400 series it fed from the side of the front grille - still looking from where on the s40), the pipe diameters are optimum and normally take a very direct route.

Only if you start to uprate other components would you need to worry about induction, but then you'd have to probably have forced induction.

Hope this answers your question.