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View Full Version : My airbox tinkering



Jesus-Ninja
19-03-2012, 12:38 PM
I've done a bit of faffing recently, so I thought I'd share what I found. No pics I'm afraid, but I'll try to get something up soon. (I know, I always say that, and then never do....)

We're all fairly familiar with the standard airbox / snorkel setup. Quite a while ago, I fitted a larger rad which was a bit too big, and so the snorkel had to be scrapped. I knocked up a new 67mm one from drainpipe elbows :vogel: and routed it to the side of the rad behind the big front grill. This seemed to work, and didn't "feel" any different to the stock setup. I had measured the cross sectional area of the snorkel, particularly the narrow slot at the front end, and 67mm was greater.

Still, it didn't seem to be right that this should be more restrictive than the MAF and pipe work on the other side of the airbox. Besides, the new snorkel was lower and so collected a lot of crap - damp gritty stuff from the road all over my air filter!

So, I moved my battery to the boot, to create a bit more space in front of the fuse box, and "modified" the front half of the airbox with a 160mm elbow. Of course this then just fed from under the bonnet, but again, seemed to work "OK", but I was surprised how noticeably power seemed to be sapped once up to temps, sitting in traffic, and particularly doing a long power run / chase.

Final step was to seal off the area and feed cold air in. I used a nice 2" thick piece of foam mat with a hole cut in it. Being foam, it seals the area off very nicely. An hour with an angle grinder and dremel and there's a tastefully cut hole in the bonnet above the inlet.

The results? I am hugely surprised, although maybe I shouldn't be. The car is noticeably quicker, in so much as the power is there straight away and stays there. I understand the physics of it, but I guess I'd always put it down to being one of those things that if you can do, will have benefits, but they'll be marginal. Not so!

Now, I'm sure that there might have been other factors involved, and my test is far from empirical (time will tell if, as with all cars and mods, it feels slower after a few days!) but it certainly works as and better than expected.

I've still to try a cone filter in the same location at the end of a decent straight pipe, but this was a £5 mod. :)

pezza
19-03-2012, 02:20 PM
.... An hour with an angle grinder and dremel and there's a tastefully cut hole in the bonnet above the inlet.



This is the part that leapt out at me :-) A very brave man or was it a spare bonnet?

I had similar surprise in increase of snappiness in power and response with the downpipe and exhaust change too...

I Would be very interested in seeing pix of the work you just completed though.. Is the inlet in the same place as the evo 7 style bonnet air intake? How large is the hole?

Cheers

Jesus-Ninja
19-03-2012, 02:36 PM
A very brave man or was it a spare bonnet?

Nope, did it in situ :) I guess I'm just not that much of a polisher when it comes to cars. So long as they work. To be honest, I really didn't want to cut the bonnet. I wanted it to stay as standard as possible in terms of appearance and trim, but I couldn't find a way to achieve what I wanted. It's a very cramped engine bay. I've also recently changed to a smaller washer bottle (two infact - one in the front and one in the boot) to clear space to get some ducting to the brakes.

adaxo
19-03-2012, 09:18 PM
Looks like good project and with some good results, I'm toying with the idea of get rid that airbox completely then fit some ss pipe elbow straight on maf facing down running as possible together with BV pipe, somehow pass it trough batt tray (or remove batt) under car and fit one of that mushroom type filters between fog light and plastic mud cover, remove one of fogs (I got that rare uk spec twin separate fogs on the shelf) to feed fresh cold air to.

scott.mohekey
19-03-2012, 09:29 PM
Did you consider cutting a hole in the area beneath where the batter was, and feeding cold air in from below, rather than through the bonnet?

Jesus-Ninja
19-03-2012, 10:36 PM
under car and fit one of that mushroom type filters between fog light and plastic mud cover

Trouble is, the filter will probably get covered in crap.

Jesus-Ninja
19-03-2012, 10:37 PM
Did you consider cutting a hole in the area beneath where the batter was, and feeding cold air in from below, rather than through the bonnet?

Yes, but there won't be much air coming in there, as I am panelling the underside of under the car.

scott.mohekey
19-03-2012, 10:41 PM
Trouble is, the filter will probably get covered in crap.

Can agree with that. I had a scary moment after the earthquakes when I had my filter in this position, and I had to drive through a heap of silty water to get home. The car started idling horribly and stalling all the time. Luckily it turned out to just be the MAF covered in dust.

scott.mohekey
19-03-2012, 11:26 PM
Yes, but there won't be much air coming in there, as I am panelling the underside of under the car.

Ah good point. Very interested to see what your bonnet looks like now.

Jesus-Ninja
20-03-2012, 09:46 AM
Pics as requested :)

51996
51998
51995
51997
51999

Humpty's Revenge
20-03-2012, 11:39 AM
If that's foam I really do hope that's fire resistant?

Jesus-Ninja
20-03-2012, 11:44 AM
No idea, Steve. It came out of a kids cot at a nursery, so maybe it is, maybe it's not! It's not particularly near anything too hot (ie tubs etc) and I'll see the flames in plenty of time ;)

Humpty's Revenge
20-03-2012, 11:47 AM
I'll see the flames in plenty of time ;)/haz

Looks good bud

pezza
20-03-2012, 11:47 AM
I'll see the flames in plenty of time ;)

hahah.. i like the attitude /yes

Well done with the cutting pretty neat!!

Have you had to turn boost down or notice any difference in peak boost?

SEAN-NZ
20-03-2012, 11:55 AM
looks like a job well done, could always test flammability by trying to light some spare stuff?

Jesus-Ninja
20-03-2012, 12:21 PM
looks like a job well done, could always test flammability by trying to light some spare stuff?

That's a good idea :)

Jesus-Ninja
20-03-2012, 12:26 PM
Well done with the cutting pretty neat!!

Cheers - angle grinder with a VERY thin disc (0.8mm) for the straight edges, and then a dremel for the corners. Finally touched up around the lip with some paint.


Have you had to turn boost down or notice any difference in peak boost?

Funny you should mention that. I have three settings on my EBC: 1 is stock, 2 is set to be just short of fuel cut, and 3 is set to be quite high. I always got fuel cut at some point on 3, but not on 2. Now I get it on 2, so I guess things are working better :)

Would be interesting to do some back to back RR tests with this and then with a cone filter.

Jesus-Ninja
20-03-2012, 02:22 PM
Looks good bud

I'm thinking I might cut back the reinforcement that is visible through the hole in the top skin. It looks better for being black, compared with the primer colour it was, but would probably be better if it wasn't there at all. I don't think it's obstructing flow particularly, but it seems odd to have cut a hole and then leave something blocking it.

Davezj
20-03-2012, 02:47 PM
to be perfectly honest, i would have thought air would have been sucked out of that hole rather than go in to the hole.
however, there is a slight angle to the bonnet so that may be enough to force it in.

i make this comment, purely because if you put a straw in a in a glass of water and blow asross the top of it, water will rise up the staws length.
i would have through you would need something to guide air downwards to make it go in to the hole like a scoope.
i am not saying it would be beneficial to guide the into the hole, just pointing out what is probably happening.


the only real way to be sure is to attach a few bits of cotton of light wool to the grill of the vent and go for a drive and see which way the strand blow. if they stik to the grill you can bet the air is going in and if they flutter about off the suface of the grill then it is probably out.
it would be interesting to know one way or the other.

but i would have thought you were waiting for this comment to raise its ugly head at some point, Sorry.

Jesus-Ninja
20-03-2012, 02:56 PM
Dave - I tested this in my S14 (see avatar), the air went in. That said, there's no harm in testing it on this as well. It's possibly worth putting a raised lip on the rear edge to stall the air flow over the bonnet.

EDIT: The better method is to use a manometer with one end on each side of the vent, to measure the pressure differential. A tuft test will just show you which direction the air is flowing. The air could be going out the hole and back, or it could be going in. The tuft would look the same. Tuft tests are better for seeing the air flow over a flat surface. Additionally, the drawing effect of passing air over an aperture at 90 degrees is fairly inconsequential compared to a pair of turbos at WOT.

Fundamentally, the car feels more responsive. It may be that for some other reason it might not be "better" (eg peak power, peak torque, 0-60) but at this end of the wedge, driving pleasure is more important.

I could do a back to back test and cover the hole if I was really worried about it.

WOODY72
20-03-2012, 03:02 PM
What you need is a pipe attached to one of the vent pipes behind the dash going through the bulkhead into the air intake. Want to go faster, switch on the aircon!!!!!! :idea2::idea2::leer::thumbsup:/woot2:rolleyes4:huh2:

Jesus-Ninja
20-03-2012, 03:29 PM
Joking aside - the "aircon cold feed" question has been floating around for a while - there's simply not enough cooling capacity. The amount of air flowing through the dash vents on a hot day is tiny compared to what a turbo charged engine is drawing in on full chat. :)

miller
20-03-2012, 03:40 PM
Nice tinkering....it looks very like the same size air intake 'hole' on my Evo 1 bonnet....it just managed to make it onto this photo

Jesus-Ninja
20-03-2012, 03:41 PM
Nice hole :)

adaxo
20-03-2012, 04:40 PM
I'm thinking I might cut back the reinforcement that is visible through the hole in the top skin. It looks better for being black, compared with the primer colour it was, but would probably be better if it wasn't there at all. I don't think it's obstructing flow particularly, but it seems odd to have cut a hole and then leave something blocking it.

I was wondering what that its and here we go , that above comment explain that all

Very nicely cut hole must admit, I was expecting something more 'bare' tbh, but now I'm well impress

This could be worth to read I think http://autospeed.com/cms/title_Undertrays-Spoilers-Bonnet-Vents-Part-1/A_2159/article.html

pezza
20-03-2012, 05:01 PM
This could be worth to read I think http://autospeed.com/cms/title_Undertrays-Spoilers-Bonnet-Vents-Part-1/A_2159/article.html

Interesting read /yes

The cowl induction hood worked wonders for my old 90s camaro but its not something that suits the galant... /Hmmm

ex-derv
20-03-2012, 05:54 PM
The amount of air flowing through the dash vents on a hot day is tiny compared to what a turbo charged engine is drawing in on full chat. :)

It's sentences like this that make me love my VR4 all the more :evil2:

Jesus-Ninja
20-03-2012, 06:05 PM
my old 90s camaro

3rd gen F body?

Jesus-Ninja
20-03-2012, 06:10 PM
Right, Dave's got me thinking now, so I'm going to test pressures properly and report back :)

Davezj
20-03-2012, 06:27 PM
i am sure the vent will work just as well eitrher way, it was just a thought.

and i forgot to congratulate you on you fine cutting of the bonnet. looks very nice.
I still have my original bonnet with the rust on it so would be a fine candidate for hole cutting.

I am not quite sure what you could use for flow measurement apart from a proper manomiter (i think that is what you call them), mamaybe mounted on the under side of the grill to see which way the flow goes. maybe it would give a positive or negative reading depend on flow direction.
but there i go again rambling!

pezza
20-03-2012, 06:40 PM
3rd gen F body?

Aye, twas /yes

I think that there was an 8g for sale with cowl hood not too long ago :-)

VR457
20-03-2012, 08:09 PM
The size of the piping is the causative factor here. There is more than enough volume of air in the engine bay to suck in without bringing it from the outside. I found gains by just putting a big nozzle / tube onto the intake. The last dyno suggests the gains were in improving low end torque and 'area under the graph'.

Jesus-Ninja
20-03-2012, 08:29 PM
The size of the piping is the causative factor here. There is more than enough volume of air in the engine bay to suck in without bringing it from the outside. I found gains by just putting a big nozzle / tube onto the intake. The last dyno suggests the gains were in improving low end torque and 'area under the graph'.

The big pipe had been on for a while before I cut the bonnet and separated the area from the rest of the bay. The most significant difference was noticed after the hole was cut more recently. As I said in the OP, before the hole was cut you could feel the power drop after sitting in traffic or on a hard high speed run.

There is no doubt that the large pipe plays it's part and that there is plenty of air under the bonnet, but that air is very warm.

Jesus-Ninja
20-03-2012, 08:30 PM
Aye, twas /yes

I think that there was an 8g for sale with cowl hood not too long ago :-)

:) I had an '83 305 a few years ago.

VR457
20-03-2012, 09:55 PM
My assumption was that by feeding the head of the pipe down near the front rad slightly cooler air could be accessed. At least the ducting would move it away from the engine.

A bonnet hole eliminates the guesswork and can provide that cooler air, assuming the airflow over it does not create a vacuum as i think what Dave was suggesting.

pezza
21-03-2012, 06:41 PM
:) I had an '83 305 a few years ago.

nice... loved mine to bits, the block was a stroked 350 so it ended up as 6.3L/383... silly torque /yes

the cowl hood mad big difference in pull...with the open air cleaner in the middle there

wintertidenz
22-03-2012, 06:21 AM
If you are going to put the pod filter on the long pipe and properly isolate it from the engine bay in the area where the battery was, I'll be interested in the results.

I was looking at doing it myself but may just build an airbox that takes a std panel filter in that area.

Jesus-Ninja
22-03-2012, 10:08 AM
I'm very pleased with the results as they stand to be honest. It was a £5 mod and has transformed response. From stock to 67mm feed from front = no noticeable difference. From 67mm to 160mm fed from under the bonnet = no better but worse with heat soak. From 160mm under bonnet to 160mm fed through hole in bonnet = startling difference in delivery, brutal even.

The alternative, for me, would be an Apexi cone - there has been some independent testing done in this area, and the results were that Apexi cleans better and flows better compared with HKS mushroom and K&N. If I could have an Apexi panel, I'd probably stick that in, but they don't do them for our airboxes. They do an evo one, so maybe shoehorning an evo box onto our MAF is the answer.

sampsulo
22-03-2012, 10:48 AM
this is something i definitely wanna do...im just not sure about the hole in bonnet...but then again what the hell.... will bum a bonnet of somewhere

Jesus-Ninja
24-03-2012, 04:34 PM
I am not quite sure what you could use for flow measurement apart from a proper manomiter

Magnehelic pressure gauge :) It's a dial with two connectors (actually, four, but you only use two) - one for the higher pressure side and one for the lower pressure side. You run pipes to these and it tells you the pressure difference.

Jesus-Ninja
24-03-2012, 04:38 PM
Magnehelic pressure gauge :) It's a dial with two connectors (actually, four, but you only use two) - one for the higher pressure side and one for the lower pressure side. You run pipes to these and it tells you the pressure difference.

I have one for doing aero measurements which does from 0 to 750Pa. 750Pa is 0.1PSI, so the amounts of pressure we're talking about are quite small, compared with a bar of boost.

It's less about ramming air in and more about making sure that the only available source for the inlet is from outside., but of course, every little helps, and I'm curious now :)

Davezj
24-03-2012, 05:11 PM
you lucky bugger,
i would have to use the clear tube manomiter (cheap and nasty) and measure it it in inches of water.
one end inside the cars cabin and the other at the point you want to measure. you would have to have 2 people in the car really to do the measuments with a water manometer one to drive and one to take readings. but it would be very crude and only rough measurements.
i have tool envy.
i will have to go out and buy something now.


boo hoo, not finding anything around the £15 mark for a positive negative gauge there some that go from 0-700 or 0-1000 Pa but they were £50
you got a right bargin.

Jesus-Ninja
24-03-2012, 05:24 PM
£15 from ebay :)

Jesus-Ninja
24-03-2012, 05:52 PM
here you go, Dave: http://www.ebay.co.uk/itm/L90-4X-DWYER-INSTRUMENTS-MAGNEHELIC-GUAGES-CALIBRATED-/370565309992?pt=UK_BOI_Medical_Lab_Equipment_Lab_E quipment_ET&hash=item564769e628#ht_2345wt_905

jjayokocha
16-04-2012, 12:35 PM
I keep wondering how on earth that small vent on the front of the snorkal even draws in air sometimes, when i close the bonnet down on mine the rubber seal seems to cover it??? I spotted this on a vr4 for sale in NZ and thought it was a good mod, would love to know how he done it.

52829

Jesus-Ninja
16-04-2012, 12:46 PM
would love to know how he done it.


Dremel? Stanley Knife? Can opener?

jjayokocha
16-04-2012, 12:55 PM
Does anyone know the car? its a red galant vr4. how has he lined the snorkal up with it too.

Davezj
16-04-2012, 01:08 PM
the standard grill has a vent slots in that position so just cut them out, or make hole a bit bigger.

jjayokocha
16-04-2012, 01:19 PM
Cheers Dave, just went out ofr a look and i see the vents in the top of it, wonder is there anyway of getting the snorkal right down behind the grill & all enclosed?