Airbox Fabrication

[L66TEY]

Has anyone created an airbox like the one in the image below, I'm looking to replicate it  

Hence, hoping someone would be kind enough to share the CAD Drawing for the sheet metal. 

With thanks

Chris 

[Ed White]

My only thought is thats a lot of surface area of filter to be fed through one of those little vents on the bonnet side?

[SLR No.77]

The bonnet hole is no smaller than the hose diameter downstream of the filter though.

Chris, have you not tried analogue CAD ... Cardboard Aided Design? It's not a particularly complex shape, basically an "L" with two folds.

Stu.

[Seabea23]

Intake air should be as cool as possible, I would have thought it could get very warm in that confined box. All the best with the project though. Chris

[aerobod - near CYYC]

Re #4, a bit of insulation on the walls of the "box" would help with heat soak, but the airflow around the filter will keep the overall temperature in the area lower, too. I don't have an intake hole on the side of the bonnet, but I used to have the filter partitioned off and intake air coming in via 1/3 of the bonnet louvres, this dropped the intake air temperature about 10C in lower speed use, as indicated by Easimap.

The only problem with my louvre intake was that it was fine with the windscreen on due to stalled air in front of the glass, but with an aeroscreen at higher speeds I could see the mixture getting too rich (with Easimap logging), presumably due to lower air pressure from the suction effect of air flowing over the rearward facing louvres. This variability of mixture seemed to offset any gains due reduced intake air temperature, so I took out the partition and went back to the filter taking air directly from the engine compartment.

The louvre intake did generally eliminate heat soak effects (such as lethargic throttle response or stumbling when pulling away) from the car idling or moving slowly in traffic at high ambient temperatures (especially above 30C), but running at normal speeds for 5 mins or high speeds for a couple of mins cleared the effects anyway.

[L66TEY]

Thank you all for your comments. 

I've since established that Arch have not made this type of airbox, however Boss Racing have - hence I've contacted Rob. 


Though you are quite right Stu, it just needs a bit of analogue CAD attention. 

In regards to the inlet, as I have no side holes of my bonnet (2010 R300D), id be looking to adding the Caterham NACA Duct that the 485 model features. 

Though it will mean bravely cutting a hole tricky shaped hole in the bonnet. 

[Toughie]

You do have a bit of a 'thing' for NACA ducts, don't you, Chris.

[L66TEY]

You know me too well Al  

Can never have enough Carbon, and hence I intend on adding not one but two Carbon NACA ducts 

One for footwell cooling, and one to feed cooler air to the air filter/plenum 

[simon_h]

I wouldn’t get too excited about the caterham naca ducts if you are hoping to put one on either side. They are quite heavily curved to suit the LHS of the bonnet only. 

[L66TEY]

Yes, its quite an awkward shape, however the one on the RHS for the Drivers footwell venting will be facing "backwards" so as to draw air out.

I started another thread on this some time back, ref;

NACA duct installation advise | Caterham and Lotus Seven Club (caterhamlotus7.club) 
https://www.caterhamlotus7.club/forum/techtalk/naca-duct-installation-advise

Chris

[simon_h]

Ok, good luck. I don’t think it will fit upside down and back to front either. It was a long time ago I did the first one so I can’t remember exactly, but it’s shaped in every direction wrong for the other side from what little memory I have of it 

[L66TEY]

Hi Simon,

Now I'm intrigued, when did you fit one (or more) of these?

As I'm about to embark on cutting the hole, having established that Arch Motors don't cut it when the manufacture the bonnet. Instead, I've understood the NACA duct hole is cut at Caterham Cars. 

Do you have any insight on this?

Having eyed up a NACA duct against the RHS the contour works - albeit need to be careful about where along the bonnet it is positioned as the radius of the bonnet front to back is not constant. 

All help/input v much appreciated. 

Chris 

[simon_h]

Back in 2012 ish when we did the 485 development at CTI. We just offered ours up and cut it out. The flange allowed a little bit of error.

If you get hold of one I'd get someone with a 485 to measure distances from rear and bottom bonnet flanges and see what happens. The other side, you are on your own really as it wasnt intended for that side and I still think it wont work.

[L66TEY]

Hi Simon,
Ah, that explains it, great to know we've got an ex CTI'r amongst us. 
I've got the NACA Duct and also access to a 485 bonnet. 
This has confirmed that there is symmetry across the two sides, but only if installed at the same distance from the bulkhead. 

However, the dept of the NACA Duct in that position on the RHS won't work - as the pedal box means there is not enough space for the NACA Duct. 

So as far as I see it, I have two options;

1) Risk trying to fit the NACA Duct further away from the bulkhead - albeit the curve of the bonnet reduces along its length, hence may not be a good fit. 
2) Seek to reduce the size of the pedal box - ideally flat as per the LHD Caterhams (eg 485). 

Hence, any input on this also appreciated, eg why is the pedal box "flat" on LHD, yet "boxed" on RHD. 

With thanks

Chris 

[L66TEY]

Simon,

Another point....

In relation to cutting the awkward shaped hole in the bonnet - being a novice at this - what tool is best to use?

[simon_h]

It would play on my mind if it were my car and I had the ducts not the same both sides?  

No idea why the LHD pedal box is lowered. Probably to miss something that had to sit there irrespective of drive side at some point in the past. Probably the airboxes when they went to the proper airbox after the aftermarket K&N style.

[simon_h]

We would have used the tool of choice for anything like that, a death wheel.

[L66TEY]

Yes Simon,

Ive had the same thought train about having the NACA Ducts positioned symmetrically to each other - but have decided "function over form" will apply. 

I believe you are spot on re LHD and the flat pedal box is due to needing the space for the airbox. 

I suggest this approach could also be applied to RHD, but I guess Caterham have not applied this change as there is no requirement to do so - apart from me wanting the space for a back to front NACA Duct 

As it happens my Caterham has the "aftermarket K&N" approach.

Thank you for the tip on the "death wheel", was thinking of using a Dremel or Fein Multi-Master. 

Either way, I'm going to need a bucket load of luck 

I've not cut any metal, but have "placed" the NACA duct in its likely position. 
 

[simon_h]

They never did a low rhd pedal box as far as I know. If you have metric then it’s all unboltable anyway so if you got a lhd one I’m sure it could be made to fit.

That duct will only extract under bonnet air like that? Not going to send anything into the footwell?

[O.G.]

Chris,

I would counsel against fitting a NACA Duct the wrong way round.

Such is the vagaries of aerodynamics I don't expect you will get any appreciable air movement out of it. NACA Ducts hardly work at all when fitted the right way round at vehicle speeds. They are there to look cool.......

O.G.

 

 

[L66TEY]

Reply to #19

It seems a extreme to "redesign" the pedal box to flat - but have to admit I'm tempted. 
And now wondering how I can get my hand on a LHD version. Though expect a RHD version would need to be folded the opposite to the LHD. 

In regards to the airflow - once I've got the NACA Duct in-situ I'll then design a duct to link the NACA back to the footwell and have it 3D printed. 
 

[L66TEY]

Reply to #20

Hi O.G.

Am conscious not everyone is a fan/convinced by NACA ducts (which ever way round fitted). 

Lots of knowledgeable opinions on a relating thread, ref

https://www.caterhamlotus7.club/forum/techtalk/naca-duct-installation-advise

I'd suggest this video confirms the principle of NACA ducts work in reverse;

Admittedly this thread has near enough turned into a continuation of the other thread. 

Albeit, I do still intend on fitting two - one each side, and each with a different purpose. 

As always, all opinions and input appreciated. 

Chris

[SLR No.77]

Chris, just an observation, but do you not think a NACA duct fitted backwards will look very odd, despite the intended purpose?

Also, if your intended use of the duct is to remove warm air from the footwell you need to be absolutely sure that a zero or positive pressure exists in the footwell rather than negative. Without doing testing my gut feeling is that due to the open cockpit, as speed increases the pressure within the cockpit will fall (Venturi effect?) in which case the reversed NACA duct will then be fighting an opposing pressure, and may well have no effect.

Stu.

[L66TEY]

Hi Stu,

On the appearance aspect - I'm not concerned. 

Though there does seem to be a fair amount of evidence/opinions that this won't work as I am hoping. 

As it stands, it's a risk I'm willing to take 

I'll press ahead

[Jonathan Kay]

"In regards to the airflow - once I've got the NACA Duct in-situ I'll then design a duct to link the NACA back to the footwell and have it 3D printed."

I'm not sure how you're planning to seal it but it needs to protect the footwell from a fire in the engine bay.

Jonathan