DIY Air box "scoop"

D

davegt

Active member
 Northant's
I'd looked at couple of scoops available but wasn't really impressed with what you actually got for a starting price of around £100 so I decided to take a shot at making one, I've seen a few made of of alu sheets and fibreglass neither of which looked great. I just happened to have a lower engine tray sat in the garage (after having to replace it thanks to a low kerb). After a bit of cutting, heating and bending I ended up with this
4.jpg

I had a bit of CF effect wrap left and it finished it off ok.
5.jpg


Not a perfect finish and it's not fitted yet either, not even sure if i'll use it or not but for 45mins effort it worked out ok
 
looks good - plenty of fresh air getting in there now. did you dyno your car before fitting this? or another note how did you get the grill out?
 
The standard intake trumpet vents off an area of high pressure to start with. Ducting to the intake, assuming that the air hitting the right hand side kidney aperture is going to flow into the intake faster because of that flow of air is ok, but I'm fairly certain it will result in no benefit, and very possibly a reduction in intake efficiency :D

The real test is to measure pre-filter air-box pressure across a range of speeds before and after fitting.

Dave
 
I actually have a not disimilar device and exactly as Mr Whippy says it replaces the trumpet that sits in a high pressure zone. I've run it with and without and it makes not a jot of difference.

The trumpet is located up in the top right hand corner behind the right grille. Fastens on with a couple of bolts.
 
Mr Whippy - I've seen various for an against topics on these types of scoops, hence why i wasn't prepared to fork out £100+, there are plently of dyno result available via google, It was more about making something up as I had the materials to hand, haven't even fitted it yet but may do just out of interest.

Doofus, Grill removal - http://www.z4-forum.com/forum/viewtopic.php?f=12&t=184 - search is your friend, as for the trumpet remove the grill and look to the right you'll see it
 
It bends out of the air-box and points into the cavity in the front of the car.

As far as I can gather, the radiator and air-con condensor need a pressure gradient to operate. Ie, high pressure in front of them, and low pressure behind.

To achieve that car manufacturers stop air in front of the radiator pack. In the Z4 this is quite efficient, and the sealing around the radiator and the area ahead of it is pretty good.

If you have a duct, or an 'outlet' from this volume, then air will be literally forced out along it. The air-box feeding from this volume is essentially getting air rammed into it from the high pressure zone. Cool ambient air at high pressure. Can't beat it.

What this flap has every chance of doing is making turbulence around the entrance to the intake reducing the pressure in that area of the high pressure volume, or causing reverse flows... god knows what.


Testing is critical to making sure you are making improvements. Easy to do with a pressure tester and some logging equipment. Manometer is the piece of equipment you want :D

Dave
 
ahh yes, i already have that site bookmarked - most informative site ive found on the net to date after porn - o i mean the z4-fourm :thumbsup:
 
so does this mean there is really no point in the RPI scoop? always wondered if they were just a money stealer...
 
They may well make a difference, but no one really proves it.

They give you questionable results, but very little data that stands up to scientific scrutiny.

No one independently tests the results to prove them valid using good method.


There are very easy tests to do to prove the benefits if there are any, but surprisingly they are avoided. The main reason I haven't tested one is because I'm 99% certain it wouldn't make any difference, or at least if it did, the change would be so tiny it'd operate within a sub 0.5% range of change which is too small to measure and assure the change isn't due to statistical noise.


Considering it's a flap of plastic, hardly a fantastic 'invention', you have to question why BMW didn't fit one to start with, but instead designed a fairly interestingly shaped intake trumpet off the end of the air-box feed. Likely designed by someone with tens of years experience in fluid dynamics and engine related ancillaries etc.


Fun to have a play for free though :D

If you're buying a tuning item, for £100 you are probably best with some kind of replacement manifolds or upper exhaust parts, or saving up towards them.

Dave
 
I have the RPI scoop and installed it at the time in combination with the BMC filter. I can not therefore comment on which element provides the changes though.

- Intake noise has increased which I like.
- Fuel consumption has dropped using the same driving style (can not comment if it was the filter or scoop).
- Car tops at 175 mph so does not seem to have suffered, but I did not top it without the combo installed though.

I have not regretted the purchase though.
 
http://autospeed.com.au/cms/A_0629/article.html

Good article, read through parts 1 > 5...

Very tempted to pick up one of those gauges since all my Z4 optimisations will be based around these kind of small improvements on intake/exhaust and possibly aerodynamics... about £115 for a 10kpa gauge and some other accessories.

I can then do some baseline measurements on intake restrictions etc, and then if someone wants to lend me anything to test with, or meet up to do some testing, we can :D

I also have a G-tech Pro RR, which can sense changes of around 0.5% in acceleration runs over 3 before averaged and 3 after averaged runs... nice!


Quite excited to do some testing. Issue is the intake testing will probably generally be proving what I suspect, that it's best left alone hehe :D

Dave
 
Fantastic - nice techy thread :D

Wouldn't logging the MAF sensor on a 3rd/4th gear WOT run to the redline work in determining its effectiveness?
 
MAF might work. Issue is MAF is dependent on throttle plate opening, and that is dictated by torque maps and driver torque request (via throttle pedal), so you could easily see a change in MAF signal, or no change, and it be due to something else changing to compensate.

Logging MAF and throttle plate position would work though I think, but it's not as quantifiable and comparable. Ie, does 1% more MAF reading mean 1% reduced intake restriction?

The manometer approach is sensible, and cheap if you have a friend to take readings and make a U shaped one DIY... :D

Dave
 
To test air-intake or aerodynamic mods you need to record the pressure with something like a Magnehelic pressure gauge connected to a tube with its end located at the test zone (i.e. in the air-filter box) and use a video camera to record what happens. You can give a commentary of the speeds you're doing whilst you are recording so that when you play it back you can see how pressure changes have occurred. I also use a DashDyno SPD and I video the two devices simultaneously, as in the photo below. The actual pressure changes that you will see are relatively small, but they can make very significant differences to performance. I use Volumetric Efficiency (VE) calculations as the basis of the effectiveness, or otherwise, of any air-intake mods, and using the parameters which I am recording on the DashDyno in the photo, are all that is necessary to produce VE figures. The DashDyno saves the data which can be transferrred to PC and the figures can be used to produce a "rolling" VE graph in Excel.

You can pick up a Magnehelic pressure gauge on ebay for very little money; mine cost £5+ p&p. The scale of 5 inches of water, or equivalent, is ideal.

48Magnehelic_and_dashdyno.jpg
 
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