My airbox tinkering

[Jesus-Ninja]

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 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]

.... 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]

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]

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]

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]

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]

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]

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]

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]

Pics as requested

20120320080646 (Medium).jpg
20120320080625 (Medium).jpg
20120320080604 (Medium).jpg
20120320080533 (Medium).jpg
20120320080454 (Medium).jpg

[Humpty's Revenge]

If that's foam I really do hope that's fire resistant?

[Jesus-Ninja]

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]

I'll see the flames in plenty of time

Looks good bud

[pezza]

I'll see the flames in plenty of time

hahah.. i like the attitude

Well done with the cutting pretty neat!!

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

[SEAN-NZ]

looks like a job well done, could always test flammability by trying to light some spare stuff?

[Jesus-Ninja]

looks like a job well done, could always test flammability by trying to light some spare stuff?

That's a good idea

[Jesus-Ninja]

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]

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]

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]

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.