Drilling holes in airbox - hole pattern?

06-22-2004, 09:00 AM

Tried a large K & N cone filter and seems to give one very loud noise - getting a bit oppressive!

so - Thinking about re-fiting the airbox cover, and drilling extra holes in the air box cover, to give a sportier sound.

Wondered if there was a 'best' number / size / pattern of holes to get a deeper sound.

From the aftermarket ones available for the newer model 911 it looks as though they have removed the trumpet, and placed 2 large holes in an opposite corner - to create a deeper effect?

Any suggestions / photos?

THanks

( ps I'm selling 2No. 9J x 16 Fuchs on e bay in the UK if anyone is looking for a pair )

Rick Lee · Rick Lee's Garage

No photos, but I used a 1.5" saw bit and drilled about nine holes toward the rear of the box - the part that's toward the front of the car. I just kept enough space between them to keep the thing from collapsing as I drilled the other holes. Those air box lids are cheap. Pick one up on eBay and play with it. On my 993 it gives a very nice roar when the V-ram kicks on. Now, with new solid motor mounts, it's very loud.

Bill Verburg · Bill Verburg's Garage

Best for that sort of mod is to cut away the whole cover leaving only the rim to hold the aircleaner in place. Next best is the largest hole you can drill replicated as many times as is possible.

Personally I would rather have an RS cold air intake,

But they only work w/ a fixed wing.

bigrubberjeep · 06-22-2004, 02:44 PM

also seen it and if you can picture the patern of dots on a die (dice) for a 5 that is the patern I saw with 2" holes
Patern looked like this

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Por_sha911 · Por_sha911's Garage

Go for the stealth look:

Por_sha911 · Por_sha911's Garage

Um, OK, now the pics:

bigrubberjeep · 06-22-2004, 04:18 PM

Quote:

Originally posted by Por_sha911
Um, OK, now the pics:

So how ya like it?

TopsailBeach · TopsailBeach's Garage

But does it really make a difference?

Por_sha911 · Por_sha911's Garage

Can't say that I feel a lot of difference in performance. I did it simply to have a nicer vroom going down the road. I tested the car with no filter or cover once and it was much louder. I would say that it's about 50% between no cover and stock. I like it.

bigrubberjeep · 06-22-2004, 04:27 PM

You like it, that's all that matters.

I drove a964 with the drilled cover too, it sounded really nice.

Wil Ferch · 06-23-2004, 06:22 AM

Guys....Bill V's suggestion is the best:
holes vs cutting the entire cover off is about the same ( aural) effect.

Also...once you have the cover cut off, you can then:
- see/feel all 4 clips that hold the cover on--- a plus
- have greater room for maintenance on the right side of the engine ( top valve cover more accessible)
- if you have adjustable Koni shocks...you can actually reach the top shaft for adjustment with the replacable white knob
- oil filter changes are easier.
- looks like "cup" lid ( which it essentially becomes) without spending $150.

---Wil

bigrubberjeep · 06-23-2004, 07:16 AM

Probably right Will - My only (side concern) has been HOT air.

Anyone have true wind tunel test done?

Dino doesnt really count since the air turbulance is not present.

- Never the less, if we are just going for better sound - Cutting the airbox works!

Venetian · 06-23-2004, 07:18 AM

I am also thinking of modifying an extra cover to to "cup" style. My concern is water entry(heavy rain). Is this a valid concern?

bigrubberjeep · 06-23-2004, 07:20 AM

Venetian - I would say it is a very valid concern - Just change out the cover dependingon HEAVY rain or NOT

When I wash my car (stock air box,no holes), it sometimes sucks little water in and back fires a cupleof times It's all better after a couple of minutes thoug.

A wide open airbox cover would suck in even more air/water n heavey rain

Wil Ferch · 06-23-2004, 07:22 AM

To answer both points:

- if hot air was an issue..I doubt the cup racing cars would allow this. There is an enormous amount of cooling air brought into the engine bay while running by the fan.
- water. The location is fairly well protected by being up front under the rear window shelf..it's not that far back under the lid screen.

No issues......

---Wil

Jim Smolka · 06-23-2004, 08:51 AM

FWIW, I have a cover that has a bunch of holes in it. Would trade, or can be purchased for a few $

06-23-2004, 08:55 AM

Two ideas / points:

Hole Positions:
The aftermarket sports cuts the extra holes over on one side of the cover - so looks as though they intend to maintain a some enclosed space under the lid for sound / boom effect?

Rain
Few extra holes along the underside of the cover ( or whatever is left of it after cutting ) would let rain drain away, and if using a K & N etc. ( see all the other threads saying they let in more dirt.... ) then this would soak up rain like a standard paper filter.

TimP

06-23-2004, 08:58 AM

p.s. - with the stock air box, Is it worth removing the 'trumpet' as it will un-clip with a bit of force!

thrown_hammer · 06-23-2004, 09:08 AM

I drilled my airbox with a 1-1/4" hole saw. I put the holes as close together as possible with maybe 1/4" between holes. I left the edges between planes as struts. I also removed the "horn". Better sound.
When someone coughs up the cash for a windtunnel test please post the results.

Nathan M · Nathan M's Garage

I did similar to the one pictured above, plus holes in the bottom. On small/partial throttle openings it's no louder than standard, but open the throttle and it sounds FANTASTIC!! Definately recommended. I left the trumpet in place. It stays dry too, and believe me, we have lots of rain in Haworth!!