Airbox modification

[caliber60]

Would you recommend this type of airbox modification? Pro and con?

thanks,

[RickM]

If you do a search you'll see there was some debate on this.

First there is the issue with whether K&N affords you hp gains or losses. Then whether or not the original air box configuration with stock filter can be improved upon.

In my eyes the consensus is that if there is a gain that it is minimal...maybe 2-3 hp and there is a possibility of hp loss.

I think the throatier sound is pleasing to some and may enhance the driving experience or at least help accommodate the perception of power gains.

[smoak]

I have done some research on this myself and agree with Rick about this. You have the above type of setup, the fabspeed type set up or custom type. All of these really are not significant in their performance for the $$$, but do really make the car sound "throatier." However, an alltogether different animal would be a MAF upgrade which would actually change the airflow substantially, which can really help performance (12-15hp I have been told if coupled with proper chip and exhaust). Anyway, IMHO i wouldnt do the above pictured unless you feel the need to hear the motor better. But thats just my opinion, maybe some of the "old timers" may have others. Good luck.

[RickM]

There is debate on whether the Hot Wire sensor conversion is worth the investment as well...at least at Autothority prices.

There are a couple of interesting threads with valuable info from Steve Wong (SteveW) describing less expensive alternatives. From what I recall some tweaking and tuning is reqired in order to squeeze the most out of the conversion.

[masraum]

That type of mod makes for more induction noise which many consider a good thing, and it makes for more room in the engine compartment. Testing has been done and shown that the stock filter flows more than enough air for the 3.2.

Cons are the potential hp loss, and it has been debated several times that these filters don't filter as well as the paper element filters and so can promote engine wear.

I'd love to clean up the engine compartment, if I was going to I would just cut the top off of the current airbox lid, that way I would retain the filtration of the stock filter but gain some room and noise.

[jmohn]

It's been pretty well documented that intake restriction on the SC's and Carrera's is not a "bottleneck" to performance (the exhaust is a different story). There is no evidence, that I have seen, that proves any additional performance with this modification to an otherwise stock SC or Carrera.

IMHO, K&N and their like is marketing not performance.

Jerry M
'78 SC

[RickM]

I used a hole saw to cut about 5-6 holes in the face of my Airbox cover.
This was a common approach in the early 90s. I'll post pics if you'd like.

[Eric Coffey]

While not a big fan of gimmicks and snake-oil, I did have the K&N Cone filter setup on my previous Carrera (for easier engine bay access only). If you go that route, you will get a nice intake note, easier access to plugs/valve covers, etc., but don't expect ANY HP gains. Also, you will need to keep the K&N cleaned and oiled (a lot more frequently then K&N recommends) to get adequate filtration. As a data point, my current 3.2L Carrera has the stock airbox, but the PO put in a OEM K&N filter, and drilled the airbox cover. With this configuration, I would say it has a better (more throaty) intake note then the cone set-up.

[fast_e_man]

If someone that has augered holes in the air box cover can post some pics that would be cool.

Also, my air box has a broken tab for the rear clip that holds the box cover. I "McGuivered" a solution with a dremel tool, but it lacks asthetic appeal. Has anyone devised a clever fix for this.

thanks,

Fast Eddie
80 SC Targa/ 3.2, 7:31
01 Liquidmatic Goped

[Adam]

More importantly, I think it was RoninLB who analyses his oil. With a K&N Filter, Ron (if it was indeed Ron, I can't quite remember) found a much higher content of silica and "dirt" in the oil.

[Steve W]

I suppose such a modification is debatable, as there does not seem to be any conclusive evidence as to it's benefit. Technical Dimensions in Florida, or maybe it's Broadfoot Racing now who's selling them, the original developer claimed he dynoed about a 4-6 hp gain from the device - what he claimed was one the the primary reasons a MAF unleashed as much power as it does, which is probably in the neighborhood of about 10 hp. Powerhaus, which has an airbox replacement of their own, in the form of an elephant trunk shaped snorkel, claims with a dyno something like a 6 hp gain on the C2/C4s which have the same airbox/intake as the 3.2s. What is the theory behind the airflow improvement you ask? It's based on the venturi ram air effect such as the stacks you see on top of a set of Weber carburetors. The "flared horn" intake allows the engine to draw air from a larger surface area than given by the size of the square rectangular hole of the air flow meter. The larger the horn's flare, the larger the surface area the air flow meter has to suck air from with the least turbulence and restriction as compared to just sucking in from a square hole in a flat wall. Some velocity stacks, such as on F1 motors, are actually are flared so that the flare practically makes a 180 degree curve all the way around, allowing air to be evenly drawn from all directions. This allows the air to gradually accelerate its velocity into the final size of the air flow meter. If you look inside your factory airbox, you will see a similar intake flare, though it's kind of small. Does it work? With a stock motor, probably minimal at best, however combined with other more dramatic modifications such as a chip and exhaust change, it should help a bit. Bear in mind, that when people dyno hp improvements from mods such as SSIs, premufflers, Extrudehoning, the hp gains are limited and controlled by the full throttle fuel map in the chip. No matter what you do, the chip is only going to provide the fixed gas and ignition timing to your engine programmed into it - the DME does not adjust (unless of course it's one of the later adaptive boxes such as in the 993s), and fuel is power. Attached is a pic of my old cone air intake displaying the internals of the design. I had this in combination with a bunch of other mods such as a premuffler, ExtrudeHoning, bored TB, porting, and a chip and regularly hard chirped my 265 wide rear tires when gear changing from first to second. As I now run a mass air flow sensor instead with a customized chip, no longer use it, but can't say it hurt it.

Steve W,

I have a K & N cone filter to use - but need the bracket / junction to connect it to the air flow meter.

can you let me know how you made the connecting plate ( the blue disc ) in your photos, what metal you used?

Also, the standard air box seems to provide quite a bit of support to the air flow meter, to stop it moving up and down - any suggestions how to replace this support once the old air box is removed?


lastly, I understand that COLD air is better ( denser ) - so would it make any improvement if:

( a) You use a longer connection tube between the airflow meter and the Cone, so the cone sits nearer the air grilles over the engine for cold air. ( with small drain hole for any rain water )
Coudl use a metal sheet, as heat sheild underneath the cone ( using the rear mounting point of the standard air box as a fixing point ?? )

( b) Try to duct in additional cold air up into the engine bay?



Thanks

[Steve W]

The connecting plate is machined aluminum and part of a kit which I think Broadfoot racing is selling. But you may want to check the MSDS design also. Colder air is denser air, which should produce a tiny bit more power. But you need to weight it out against the longer travel path. I forgot who it was on the board who experimented with such an idea with the 993 airbox. He measured something like a 10 degree difference from the stock location to the colder air he could draw directly from the grill right under his tail's deck. But then you may be looking at something like this, which I have yet to hear of anyone trying:

[RoninLB]

Originally posted by Adam Chaplin
More importantly, I think it was RoninLB who analyses his oil. With a K&N Filter, Ron (if it was indeed Ron, I can't quite remember) found a much higher content of silica and "dirt" in the oil.

yes Adam.. it was me.
I compared the K&N used in metro NYC streets to the stock filter used on big dirt off road Nevada trails.. and the stock filter had a lower silica content in the oil.. but anyone can compare the two filters this way. so I may not be the last word on this. I used oil man Larry Turner that hangs on the Rennlist e-mail board for the oil analysis.

[RoninLB]

here is one dirt road dirty 911

Fitted a K and N filter to my carrera 3.2 as per the pic in caliber60's photo in the first post. ( it just clears the the engine cover hinges.

I get a weird, continuous sucking noise from the air intake now!
bit like what was described by people using the Ecotek valve.

Difficlult to tell if there's any more induction noise, as I hadn't driven the car for a month or so.

I have drilled holes in our old Audi - and immediately noticed a huge difference in induction noise, so is it just that the 3.2 porsche engine is noiser to start with???

[stlrj]

Personally I prefer the look of the stock air cleaner.

The K&N filter look sends a message to me that whoever did this knows absolultely nothing about performance and is only doing it to tell the world " I don't know what the h@#! I'm doing."

Cheers,

Joe

[c2 rower]

That open K&N filter just makes a lot more noise. It's not worth the hassle. It might sound neat for a while but I grew tired of it. Keep the OEM box and get a chip from Steve Wong.

tried some ' enthusiastic driving' with the roof down - and still don't think the engine sounds any louder / deeper with the K & N Cone filter fitted.

THink I'll try the 'holes in the airbox' mod ( DIY version )

with / without a stock air filter - any suggestions?

[greglepore]

For the adaptor plate, you can now get something similar at Autozone for under 10 bucks. It might require that the bolt holes be redrilled, but it'll work.