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B6 S4 Bonnet vents ??
Posted: Fri Sep 07, 2012 8:40 am
by linkman72
I have recently fitted a filter element to my S4 ( the first minor mod ), I would prefer a CAIS but this will do for now. I know the V8 in a little engine bay means it runs warm so I was wondering if anyone has fitted vents to the bonnet and or fed a decent air filter from them.
I was planning on buying a scrap B6 bonnet and playing but if anyone has seen a decently modded one I would rather check a few designs before I crack off the grinder, I had thought about two nascar style ducts at the rear centre of the bonnet to feed directly into the 'V' but with second hand bonnets being £50 plus I dont want to make too many errors. The reason I say this is my old Sierra 24v cosworth had a similar set up with a sealed in cone filter feeding from a bonnet vent and it ran really well on a £50 green air filter
And I think a scooby vent will be a bit much ( I would rather have subtle functionality over slap ya face race mods )
And no I aint Vin Diesel and dont want a flappy carbon one before you say it ta
Re: B6 S4 Bonnet vents ??
Posted: Fri Sep 07, 2012 9:08 am
by goose
Re: B6 S4 Bonnet vents ??
Posted: Fri Sep 07, 2012 9:26 am
by adsgreen
Bonnet vents usually are not the best source to get engine air from.
All the vents I've seen are used to cool something - often on FI cars it's used to cool the chargecooler.
Subaru is actually using it as an engine feed but thats why it's as big as it is. If you want subtle then no good for direct air engine feed.
NACA ducts are often used as there is vitrually no drag penalty - developed by nasa in the piston engine aircraft days as a way of cooling engines without having to stick a massive radiator into the airstream. They work very well on cars on both top and bottom sides (RS4 has several on the undertray).
You've got really two options though - "Air in" and "air out". Things such as naca ducts, scoops etc will grab air into the engine bay. Vents and grills will let air (and heat out) - think Aston MArtin V12 vantage for a relatively extreme example.
My advice would be that if you have a specific need (such as a radiator or somthing else requiring cool air) then a naca duct with some direction is the best way forward. The downside to this is that naca ducts operate in a very specific way so they need to be oriented and positioned exactly right in order to be effective. With the RS4 they are useed in a general way and there's lots of them to get the airflowup into the engine bay (these are probably more to cool the headers and the surrounding areas).
If you don't have a specific need other than to reduce temperatures then stuffing more cold air into the bay may not work as well as you might think. Sure it will work no question but you need to consider that the extra air has to get out somewhere. This is why a vented/grilled bonnet can work wonders - the natural airflow over the top of the car will create a low pressure area so they'll be some good extraction forces at work. It also allows heat to not be trapped under the bonnet and you can also position them more freely asthetically comapared to scoops and ducts.
Re: B6 S4 Bonnet vents ??
Posted: Fri Sep 07, 2012 9:29 am
by adsgreen
IIRC the MTM one was more to get the blasted supercharger to fit
Have to say I prefer colour coded vents/scoops/ducts.
Bonnet vents are really hard to get right without looking a bit... max power chav.
Re: B6 S4 Bonnet vents ??
Posted: Fri Sep 07, 2012 9:31 am
by adsgreen
Re: B6 S4 Bonnet vents ??
Posted: Sat Sep 08, 2012 11:31 am
by linkman72
Cheers for that, those carbon flappy bonnets are a bit extreme for me I will experiment with some universal cut in subtle vents for now and look at air feed later