Cold air intake for an NB & aerodynamics.

poison · Post by **poison** » Thu Feb 14, 2008 5:36 pm

Has anyone seen some good idea’s for cold air intakes on an NB? We’ve all seen the headlight duct on the NA which IMHO looks great. But what about the NB. Some people also claim this to be a ‘low pressure’ zone so very little air gets taken in (I don’t agree) but don’t actually know.

In about the same place as the NA I have a K&N Tube style filter, but this is only 300mm away from the turbo. I can’t go down through the flat panel behind the lights as this is where my IC pipes run, so I really need to get cold air into this spot. Has anyone seen a tasteful/subtle bonnet scoop anywhere I could maybe copy? Also has anyone read any reviews on this sort of thing? Come on JIF, this is all about you…..

I have just got a couple of small bonnet vents from a WRX that I am “thinking” of putting in the mid-upper sides of the bonnet (a little further back than they would be on a WRX – see pic below – or I could even move them right forward). Does anyone know if this would in-fact allow air in or out of the bonnet? I ask this as I don’t want additional engine fumes while toodling along. There was an MX5 NA bonnet in black I think on TradeMe recently with these WRX grills in it, and they looked good, quite subtle.

Post by **jif** » Thu Feb 14, 2008 5:52 pm

ok, i'll bite ... it's not so much that the headlights are low-pressure, but they are low-ER than the engine bay at speed. On an NA you can have the headlights up at speed and see the raindrops deflecting fwds as you drive !

How about a Loch / Randall style cowl intake (thru firewall) ?

The bonnet vents seem like a good idea, tho I haven't done that. Still procrastinating on that one!

one other thing, my intake moved from in the nose to behind the radiator (hot!) but intake temps haven't noticeably changed. That would be the intercooler doing it's thing...

... so err.. if you're intercooled I wouldn't worry about (turbo) intake temp. Only the temps before it enters the engine.

Post by **zorruno** » Thu Feb 14, 2008 8:30 pm

You could keep a bit of tradition alive and look toward the 80's Group A Mazdas...

Post by **zorruno** » Thu Feb 14, 2008 8:34 pm

Or how about this to say 'I have real heat issues...'. I've seen a few GTX/R 323s and Familias with setups similar to this over the years

Post by **zorruno** » Thu Feb 14, 2008 8:51 pm

poison wrote:Some people also claim this to be a ‘low pressure’ zone so very little air gets taken in (I don’t agree) but don’t actually know.

I think you will find that the above Mazda ones are designed for low pressure extract... the Subaru one will be intake as I presume the intercoolers are on top. These Mazda ones were always to quickly extract air flowing though the front mounted radiators/intercoolers.

I believe there have been a number of people that have measured the bonnet areas on the MX5 and they all found higher pressures at the base of the windshield (good for cowl mounted intakes) and lower pressures across the bonnet (good for extracting hot air). Sorry - can't find any actual www evidence for you at the mo though...

poison · Post by **poison** » Thu Feb 14, 2008 9:08 pm

Actually, maybe I should do a little experimenting, I'll use a Differential Pressure Sensor and pipe one side under the bonnet and the other on top at a few points across the bonnet and see what I get. I'll need a wingman to take readings for this one, Jif lets catch up soon and play. Sorry Z this is analogue tech stuff, not Security - Bonnet is open - Bonnet is closed - or even a video of the bonnet open and closed... lol

petercristina · Post by **petercristina** » Thu Feb 14, 2008 9:13 pm

We had an air scoop under the front of the car with about a 10cm diameter tube running up by the engine pointing to the KN filter.

Post by **jif** » Thu Feb 14, 2008 9:18 pm

there's some articles like that on autospeed.com (got the URL right this time). It's under aero or wool-tuft testing... something like that...

poison · Post by **poison** » Thu Feb 14, 2008 11:25 pm

petercristina wrote:We had an air scoop under the front of the car with about a 10cm diameter tube running up by the engine pointing to the KN filter.

This is the kind of thing I wanted to do but how did you get it into the engine bay? If it went underneath the radiator it would be too low. I can't find any obvious places to run one.

petercristina · Post by **petercristina** » Fri Feb 15, 2008 12:59 am

The scoop is under the radiator.The opening is wide but flat. I did have to replace the plastic ties once after rubbing on a raised parking barrier.

petercristina · Post by **petercristina** » Fri Feb 22, 2008 11:12 pm

http://www.eautoworks.com/html/ape-auto ... ~Scoop.htm

brownie · Post by **brownie** » Tue Apr 01, 2008 10:33 pm

check the setup on my car ,suitable ?,Came in from Japan that way ,lovures either side of the hump and inlet over the top of the HKS filter ,Similair design might work ,Still uses the alloy bonnet and can't see any marks where they cut it,done very tidy.
The challenge would be finding something to suit ,Pluming supplier maybe?

Habanero666 · Post by **Habanero666** » Mon Apr 14, 2008 7:37 pm

This could help you decide between, excessive engineering or simplicity.

Air density drops 3.3% for every 10*C rise in temp. FACT

It's hard to fathom a difference of more than 30*C under the bonnet above ambient air temp for a moving car (this is when the car will make power...not at idle).

This represents an air density drop of 9.9%. FACT

Ok, if say a POD filter flows 9.9% more air than a COLD AIR DUCT system, the pod wins. And guess what? it will. The pod will win even more convincingly if the temperature of the intake air is less than 30*C!

Dont believe me?

PV=nRT

Where,
P= pressure in Bar
V= No. of molecules in gram molecules (aka density)
R= universal gas constant (= 0.0821)
T= temperature in degreesK =degrees C + 273

Rearrange the equation to put temp and density on opposite sides... this now gives us,
n=PV/RT

We are after all concerned with intake temps which is occuring at 1 bar constant ( at sea level), the volume is taken as 1 cylinder full ( for example my 1.6L engine divided by 4 = 0.4L/ cylinder).

Ha ha ha ha! but could be anything due to forced induction or differences in Volumetric efficiency ie cylinder fill etc! but this will show you roughly how it works

Alrighty! now we can solve the mystery at 0*C,

n= 1x0.4L / 0.0821 x 273
= 0.4L / 22.4133
= 0.01784 gram molecules/cylinder

Again for 30*C

n= 1 x 0.4L/ 0.0821 x 303
= 0.4L / 24.8763
= 0.01607 gram molecules/cylinder

so... the difference between the air density at 0*C and 30*C is,

100-(0.01607/0.01784x100)=9.9%

What this proves, is that the relationship between temp and density is linear within normal driving limits.

So therefore it applies to the % difference between 20*C and 50*C.

Pods win

???

Habanero666 · Post by **Habanero666** » Mon Apr 14, 2008 7:54 pm

RE: Jif :
one other thing, my intake moved from in the nose to behind the radiator (hot!) but intake temps haven't noticeably changed. That would be the intercooler doing it's thing...

... so err.. if you're intercooled I wouldn't worry about (turbo) intake temp. Only the temps before it enters the engine.

I have the same result......so thats why it pays to stay at school!!

[/quote]

Post by **jif** » Mon Apr 14, 2008 11:13 pm

confession time... actually the filter got moved back into the nose (from behind the radiator) cos I did notice that power was down quite a bit with the hot air intake. I can only theorise

(as I didn't datalog) that it was because of the less dense compressor-intake air causing the compressor to flow less... like being at high altitude I theenk...

lesson learned !

Habanero666 · Post by **Habanero666** » Tue Apr 15, 2008 8:43 am

[quote="jif"]confession time... actually the filter got moved back into the nose (from behind the radiator) cos I did notice that power was down quite a bit with the hot air intake. I can only theorise

(as I didn't datalog) that it was because of the less dense compressor-intake air causing the compressor to flow less... like being at high altitude I theenk...

Aha! You have a confession!

I have noticed a difference of about 6*C intake air temp, if I have a cold air pipe blowing onto my pod set up. The pod resides on the end of the turbo facing forward and the pipe collects air from the front of the radiator. This works very well, without having to transform the intake of the turbo into an elephants trunk with all the associated restrictions!

I have noticed with the FM link software, the temperature- map adjustments are very accurate and that if for any mechanical reason, the system should see an oddity ( temp spike/ boost spike etc ) it will not even go close to knocksville.

I have a confession also!

A Monster intercooler water sprayer will decrease the intake temps at 12psi boost down from 30*C to 22*C ( short blasts on boost to get the temps up) with a highly efficient FMI selected.

At 14psi boost it will only control the temp rise by 4*C ( this test was conducted over two seperate days of roughly the same ambient temps of 22-24*C), Also I have noted the td04 turbo I am using is running with double hinged knees at these boost levels!! Which will effect the systems thermal effeciency a considerable degree.

So obviously boost has an effect on engine intake temps and would additionaly effect the underbonnet temps.

I can only assume that by placing a cold air intake on a turbo system, you will, depending on the set up, achieve an overall lower operating temp of the entire system. Turbo, intercooler pipes, intercooler, throttle body, manifold, engine,exhaust.......Start with lower temps....finish with lower temps.

Ahhhh... the simple recipe for power

Post by **jif** » Tue Apr 15, 2008 9:15 am

sounds right - I've noticed before that the EGT (exhaust gas temp) will rise with the coolant temp too.

SLYDIT · Post by **SLYDIT** » Wed Apr 16, 2008 1:47 pm

have a look at my cold air box system on my car.(click link on my sig) reduces air intake temps significantly as measeured by my k type thermo couple meters.

Gravelben · Post by **Gravelben** » Wed Apr 16, 2008 3:09 pm

petercristina wrote:We had an air scoop under the front of the car with about a 10cm diameter tube running up by the engine pointing to the KN filter.

The thing to be careful of with a setup like that is water - heard an unfortunate story about a 300ZX getting its engine hydraulic'd by hitting a deep puddle with an intake too low to the ground.