drilled airbox?

Tue Jan 16, 2007 11:55 am

lancelot wrote:One of the previous cretins who owned my M3 did this mod. Totally pointless. Think about it, you have a pipe, air goes in, if you the cut holes at the bottom of the box the air will take the route of least resistance, ie instead of going up through the filter it goes straight out through the drilled holes. Therefore you reduce the amount of air your engine flows, which ultimately reduces power. Possibly one of the most stupid mods I have ever seen. Don't do it.

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.

Tue Jan 16, 2007 4:05 pm

I think lancelot was working on the premise that there would be a higher pressure area beneath the filter, similar to the ram-air effect employed by some motorcycles and the Bristol Fighter among others. As far as I'm aware this isn't the case where the E30 is concerned. Any difference in power from warm air entering the filter is going to be within a couple of bhp in a normally aspirated engine travelling at speed. Seeing as the original poster wanted to have a decent induction roar for a few quid we may be in danger of analysing all this just a bit too much.

Tue Jan 16, 2007 4:32 pm

why not go the whole hog and drill some holes in the rear back box for the ultimate boy racer effect !!

Tue Jan 16, 2007 4:33 pm

Ziggy wrote:
lancelot wrote:One of the previous cretins who owned my M3 did this mod. Totally pointless. Think about it, you have a pipe, air goes in, if you the cut holes at the bottom of the box the air will take the route of least resistance, ie instead of going up through the filter it goes straight out through the drilled holes. Therefore you reduce the amount of air your engine flows, which ultimately reduces power. Possibly one of the most stupid mods I have ever seen. Don't do it.

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.

just to add to this, at 70mph how warm is the air going to be passing the air filter !

Tue Jan 16, 2007 4:35 pm

Ziggy wrote:
noney82 wrote:dont k&n do cones i use to have one on my nova (stop laughing lol)
Yep - that's what was on my car when I got it. Nice noise ( ) but I got shot ASAP for all the reasons mentioned above. Plus I wasn't gonna pay my insurance company to have it fitted!

i wouldnt even tell them i fitted a filter

Tue Jan 16, 2007 4:49 pm

tim-ix wrote:I think lancelot was working on the premise that there would be a higher pressure area beneath the filter, similar to the ram-air effect employed by some motorcycles and the Bristol Fighter among others. As far as I'm aware this isn't the case where the E30 is concerned. Any difference in power from warm air entering the filter is going to be within a couple of bhp in a normally aspirated engine travelling at speed. Seeing as the original poster wanted to have a decent induction roar for a few quid we may be in danger of analysing all this just a bit too much.

Agreed. & you're right on ram-air being an irrelevance here too.

m-dtech wrote: just to add to this, at 70mph how warm is the air going to be passing the air filter !

Quite - Sal's done tests on the subject & concluded the same.

noney82 wrote: i wouldnt even tell them i fitted a filter

I would! Because I don't fancy the idea of having an accident with invalid insurance.

Tue Jan 16, 2007 6:02 pm

oh well i done it today i drilled 6 3mm holes but theresnodifference? am i supposed 2 drill more?

Tue Jan 16, 2007 6:56 pm

Yeah, that's not enough to make any difference really. I'd have thought you wanna enlarge the holes up to about 15mm for a start, then bigger if you feel the need...

Tue Jan 16, 2007 11:16 pm

lol i was really trying hard to hear a different sound but it was still the same, ill try again tomorrow, hopefully 3rd time lucky!

Wed Jan 17, 2007 11:33 am

Ziggy wrote:

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.

Just to be pedantic, the air is actually pushed in by atmospheric pressure...

Wed Jan 17, 2007 12:54 pm

ChizFab wrote:i no its on a ford but,

in an old fast ford mag a couple of years back, they featured a rolling road, where various modifications were tryed out on a 90spec escort xr3i. they actually found that drilling the airbox gave somthin like 3 bhp more than any of the aftermarket filters such as k&n, green etc!!!

lol thot is was great at the time n promptly set about my mates 3i with the drill!!!!!

yes but fords are proper sh!te out of the box, they need all the help they can get. Horrible things

Wed Jan 17, 2007 12:58 pm

hoshy wrote:
Ziggy wrote:

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.
Just to be pedantic, the air is actually pushed in by atmospheric pressure...

I'd say a combination of both! The only reason more air is pushed in through the holes is because the existing air is sucked into the engine!

Wed Jan 17, 2007 1:02 pm

Davenotouring wrote:
hoshy wrote:
Ziggy wrote:

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.
Just to be pedantic, the air is actually pushed in by atmospheric pressure...

I'd say a combination of both! The only reason more air is pushed in through the holes is because the existing air is sucked into the engine!

Damn, beat me too it!

Wed Jan 17, 2007 1:04 pm

this is the ultimate council mod, adds 10bhp at the spare wheel

Can we add a new section?

Council Spec: for all your council needs/mods.

Promote cliffybabe as the mod for it as he has the right credentials with BK's and chrome arches

Brian can you put it to the team?

Wed Jan 17, 2007 1:06 pm

Simon, you could be the council suspension guru?

Wed Jan 17, 2007 3:34 pm

hoshy wrote:
Ziggy wrote:

The reason power's potentially reduced is because (warmer) air is sucked in through the new holes. Air's being sucked through the filter, not blown.
Just to be pedantic, the air is actually pushed in by atmospheric pressure...

Now you're just trying to confuse people!

Wed Jan 17, 2007 3:38 pm

Mine's drilled. By the previous owner though. Didn't know until I took it to bits and found mouse sized holes in the side and bottom. (pre-filter side, thank god)

Suppose it sounds okay.

Each to their own though I guess.

Wed Jan 17, 2007 8:43 pm

oh well i finally done it today mostly for my son as my previos 325 had k&n n he loved the sound and am pleased with the sound, thanks for evry1s help

Wed Jan 17, 2007 11:22 pm

Well, not quite sure that air is sucked in. On the E30 M3 the snorkel exits into a low pressure area so that air will be pulled into the airbox (a kind of ram air effect). I would be very surprised if the pressure within the airbox itself is so low that it scavenges air. Either way, attacking your airbox with a drill doesnt seem to wise to me.