is the stock air filter on the 3.2 restrictive
 

Hello,

Notice some swap out the stock air box for a cone filter. Is the stock air box know to be restrictive?

Thanks,

Chris
89 Carrera

No, not really.

Agree with gtc. Some have pointed to the "barn door" on the AFM as being less than desirable, but moving to a new AFM is a much more complex and costly swap.

Many threads spend time trashing the KN option as being a poor filter and gaining nothing measurable other than physical space sometimes. I think the KN is a yearly PIA to service so I removed the one that came on my car which was a drop in replacement for the stock filter fitting the same housing. Back to stock paper. Cutting the top off the stock airbox supposedly results in some measurable increase of performance. Would make reaching the box clips easier if your arms/hands are big.

Dyno numbers
 

Does anyone have any Dyno numbers to actually give real results? The filter or housing would have to be the flow limiting point to make any difference I would imagine.

Think that answer is yes, you'll have to do some searching/reading. Could be some of that info. with regard to Steve Wong performance chip. Basically key on the very few incremental improvements that you just drop in.

Porsche was pretty good on the engineering for the intake and exhaust of the 911. The Electrical and AC engineering sucked big time, but the performance of the intake and exhaust is hard to beat by more than a few HP. Steve Wong showed that with the stock intake just removed, it was almost no gain or very little. You really need the filtration of the filters.

A few HP can be gained on the exhaust if you don't want to have heaters. I really like having heat so that ain't an option for me.

Changing the airbox will net you a different sound with no HP gain. You could lose some though. I have an MAF conversion on my car. It makes no difference over the stock box.

Airbox is not a restriction. The same general airbox is used on the 964 3.6 and that engine easily makes more power and torque. Swapping out that box on the 3.6 nets very little, if anything, in power gained on that engine too. So in my mind that too proves that the airbox is not a restriction.

A lot of the cheapo cone filters that can be adapted to the air flow meter are actually a bigger restriction. I grabbed a cheap Spectre brand piece of crap from a local Pep Boyz (purposely misspelled........... :D ) to do a comparision. I did this because my friend with the same 3.2 Carrera 911 as mine, who is a pro mechanic, put on one of these crappy horseshiat filters. I measured the length and depth of the Spectre filter pleats and compared that to the typical original paper filter surface area. The difference in surface area was huge in favor of the original filter element. So my point is, your cone filter has to be quite larger in order to have the same amount of filtration area as the original filter. That said, i'm sure the cone filters have a less restrictive filter element and that makes up for the lack of surface area.

I seem to remember Bruce Anderson (RIP) said that leaving the filter and filter cover off caused a 3 hp loss in power.

Yeah, but it SOUNDS like it's got lots more... ;)

Recently drove a completely stock 60k mile 1987 911 and a coned, chipped, dual outlet exhaust and who all knows what else 80K 1987 911. Not really a fair comparison without testing leakdown or knowing condition or correct plugs plus valve clearance, but back to back the stock one was noticeably quicker down low, in mid-range and top end pull.

The answer to the original question is probably NO... However, Porsche left 20-30Hp on the table for the US version of the 3.2L. The biggest gain potential is probably on the exhaust side.
With an opened up airbox, MAF sensor (ditch the AFM barn door), extrude honed intake, bored out throttle body, good headers, a low back pressure muffler, and a good tuned chip, you might get 250Hp on a good day. All for around $5-6k...

Save for the TB extrude honed intake, I have all the mods described above and it pulled about 200HP at the wheels. 150K mile motor. 50K on top end. For comaparison, it pulled about 5 HP less before all the work. Expensive ponies. Sounds great though. Muffler is two in one out. Steve Wong chip.

This is what I personally observed when I was watching a Steve Wong chip custom tuning session on a buddies 87, it was not planned, for the heck of it after his car was all tuned up we swapped to OEM paper filter without the bugle cover and gained 4-5 HPs consistently with 3 runs on the Dyno, needless to say he kept the paper filter in place. ;)

I went home and swapped back too plus cut the bugle off

1988 3.2, 56,150 miles, stock air box with open cover, stock filter element, Web 20/21 cams, pre-muffler, single in / out Dansk SS 84mm tip sport muffler...

Baseline: 193 hp / 168 tq

Same engine configuration, one hour and ten minutes and nine dyno pulls later, Steve Wong working his techno wizardry on the ECU tune...

+ 19 hp / + 18 tq = 212 hp / 186 hp

I know this doesn't fully answer the OPs question, but it seems to support the stock filter element and AFM as being "adequate."

http://forums.pelicanparts.com/uploa...1501483402.png