Dave East

Hi all

Just about to fit a K&N induction kit to my classic turbo. Just wondering what people have doen in regards to the bonnet vent.

Obviously removing the covering plate will increase the flow of good ol cold air, but the filter stands the rsik of getting wet. Have people overcome this problem? I was thinking perhaps of a 'stepped' air flow.Thus allowing the air to flow but stopping the majority opf water ingress.

Any ideas would be great guys! Also, hjas anyone itegrated the bonnet vent into a cold air box? Justa thought.

All the best

dave.

Triple X

iTrader: (1)

Just refit the blank if weather gets bad. 2 mins of a job

Mo

I'd want to monitor the temps with and without to confirm your thoughts before worrying about water ingress.

Aztec Performance Ltd

iTrader: (234)

Opening the vent may draw the warm air towards the filter, which is the opposite of what you are trying to achieve.


Bob

Peanuts

iTrader: (15)

ah, the old Chimney effect.
good point, well made/

Jolly Green Monster

iTrader: (4)

yep tried it with temp gauge and it got hotter!

Triple X

iTrader: (1)

What about a mini scoop?

Nick Read

I did quite a lot of research into this with my old car, especially modding intakes and airboxes etc, and as someone else pointed out above, it doesn't necessarily follow that opening up a hole in the bonnet will increase airflow - or at least not in the way that you want. Mini-scoops are ok but even these will not necessarily get any airflow IN to the bonnet, even if they look like they will. What you need to do is get an idea of the pressure differentials in different places across the bonnet and under it. Make yourself a water manometer out of a length of wood and a load of fish tank tubing, with one open end inside the car and the other open end at the place where you want to measure pressure. Take the blanking panel out of the vent and measure air pressure on the outside and inside of this area. Higher pressure outside than inside indicates that air will naturally flow into the vent. Vice versa means that air will naturally flow outwards.

I reckon it is more likely that air would be flowing out through this area as the top side of the bonnet half way along its length is likely to be a fairly low pressure area and inside the top of the engine bay is almost certainly a relatively high pressure area. This would explain why people have noted higher filter temps. Obviously, I'd have to test it to be sure, which I will do at some stage.

At standstill or very low speeds, without any significant air pressure issues either under or above the bonnet, heat will be the deciding factor and in this case an opened vent will definitely flow air outwards and upwards, conveniently warming up your air filter nicely as all the engine heat rises past, towards the only exit that it's got.

I guess the moral is, with aerodynamics, don't assume anything.

Scoobynodd

iTrader: (1)

hiya fella,

Don't want to sound like i'm trying to pee on ur bonfire, but if ur car's turbo set up is the same as mine (mine's an early 96, with a 'top entry' turbo, NOT front entry) then i hope u hav'nt purchased the same K & N kit tht the monkey of a previous owner installed in my vehicle bcos to b quiet honest, its shiiiiiiiiiiiiiite!

I'm saying this bcos my version has a little bracket arrangement that attaches to the end of the cone, and secures it to the inner wing! - WHAT A WET IDEA!!! Bcos whats happened now is, bcos the cone and air intake pipe are secured in place (bear in mind ur engine from time to time, vibrates from left to right!), the inside corner of the 90 degree elbow has been weekend and split, and also the cone itself has (i'm guessing, over time) developed a crease around it (so it just looks a bit daft now). My thoughts are, simply, don't secure it to the inner wing using tht daft bracket, just leave it be (hanging) and see how u get on, or maybe fashion urself another way of securing/supporting the inlet, after the cone.

My next wee job is to purchase the HKS green mushroom item (jap stuff in my experience, has just always been farrrrrr better on jap cars, than british stuff i.e. K&N) simply bcos its a far better kit (altho weighing in at around £155) its mushroom has a far bigger surface area than the K&N cone, dos'nt take uphalf the room under the bonnet as the elongated K&N jobbie, is'nt secured to the inner wing, (<<eventually 'folding' stuff), and is instead support on 'legs' underneath, bolted into the original airbox holes.

If u like, drop me a PM with email, and i'll send u some piccies of whats going on under my bonnet, to better explain.

Ohh an another idea - the same monky who fitted tht item, also installed a cold feed tube, from under the frikken radiator (so right at the bottom of the car, which looked daft from the outside - a tube pointing at ya lol!), up the back of the radiator and terminated pointing at the cone, not a bad idea in theory, but!, THT low down to the road, at this time of year, is only gonna pull in spray, muck, moisture, road film, and other offending substances straight from the road surface, so don't go 'donw' tht route, or tht low lol, stick with ur bonnet area idea, nice n high up, at least tht way, u may only catch the odd fly ;-)

Dave East

Cheers for the advice guys! Excellent as always.

Gonna have to investigate some of the issues that have been raised. I think I will fabrictae a cold air box, with an external supply from somewhere cool and dry!

Scoobynod - thanks for the advice buddy! My car's a MY99, but as far as I can tell, the mounting brackery is the same old lame piece of monkey metal!! Luckily, I am an engineer! So I have plans to weld up some custom struts to completely remove any vibrations (esp. as I have the dreaded MY99 chocolate MAF!!)

Once i get everything fitted I'll post some pics.

Also, if anyone needs any brackets made up, if you supply a drawing I can pretty well make up most things (Stainless Steel or aluminium). And I'm nice, so I won't charge you much!!!!

All the best

Dave.

Nick Read

Well, a cold air box WILL probably work pretty good with a mini-scoop. Fab up a box with an open top with its top edges covered in pipe lagging/draft excluder etc so that when the bonnet comes down it seals to the underside of the bonnet and creates a closed air box. THe only opening will then be the scoop which will then work properly, because the airbox underneath it will be in vacuum most of the time. No need to start trying to sort out convoluted air hose here there and everywhere, the cold air's there for the taking, you just need to know how to get it flowing where you want it.

To be perfectly blunt all these engine bays you see with a damn great hose running from the bumper or under the rad, or inside the wing, they're just pissing in the wind - literally. The effect of the pressure differentials under the bonnet means that most 'cold air feeds' just contain a small amount of stalled, useless air that dribble out a feeble trickle of cold air, somewhere near the induction kit. That's fine if you haven't got an engine, gearbox, exhaust and turbo giving off huge amount of convected and radiant heat, not to mention a bloody great radiator, intercooler and possibly aircon doing a great job of making lovely hot air inside the engine bay!

BTW I'm not totally dumping on open induction kits. They have their uses and for high power turbo applications I have no doubt that big induction cones are the only practical way to get serious amounts of airflow through a turbo. Where hefty intercooler/chargecooler capacity and effective engine bay heat management is a given, then big cones make sense because inlet temp before the turbo isn't the major issue. For standard and mildly tuned road cars the charge temp that enters the filter is the most important consideration, because in general whatever the filter is, it's likely to be doing the job adequately in terms of flow.