Bob Rouleau

Steve - the magic of the 993 was that POrsche had to restrict intake noise to meet the regs in Switzerland. That's why they left HP on the table. The motor-sound package was not offered in certain markets where noise was an issue. I don't know if the 996 suffers fromthe same weakness.

On noise, I was told by an insider that the Sport Exhaust was designed to avoid the Swiss regs. If you hook it up as per the book with a new ECU and wiring, the exhaust goes into quiet mode at those speeds and RPMS tested by the Swiss. Clever devils those PAG engineers!

Steve in FL

Bob: My understanding was the Motor Sound Package wasn't offered for the 996 as there wasn't anything left on the table. Hence my joke about 996 owners drilling holes to no avail.

Philip in AL

Bob Rouleau
Number 2 and 3 contradict each other.
<<2) If the surface area of the filter does not change, the only way to get more air to the engine is by doing less filtration. What impact does this have on engine longevity?

3) Bruce Anderson tested so called low restriction air filters on a dyno and observed no horsepower gain with a K and N he went even farther and tested the engine with no air filter at all and observed no useful gain IIRC this was on a 3.6 liter 993 engine. They did get about 7 HP more by drilling holes in the 993 airbox cover though. >>>

Drilling holes in the air box did not change the sufface area of the filter, nor the % of filtration.

Z06

Info at K&N http://www.knfilters.com/facts.htm

Z06

Here is one more http://www.bmcairfilters.com/VisDyno.asp

jgerken

Bob,

Let me see if I can handle a response to Philip in AL.

2) With the same overall surface area, one filter would have to have a greater % of its surface area occupied by gaps and less occupied by filter material. To get this greater %, the gaps through which air flows would be larger, allowing more and greater size dirt particles into the engine, causing increased abrasion and deposits.

3) In the 993 engine, the airflow bottleneck was the intake opening to the airbox, not the filter. By drilling holes, you increase the flow of air into the airbox and eliminated that bottleneck. The next greater restriction may have been the filter or it may have been some other part of the intake tract.

jgerken

Interesting reading on K&N's web site posted by Z06.

Philip in AL

So what you are saying is, yes it is possible to get more air into the engine, with the same filtration and the same surface air filter area. Kinda like having a higher BUS speed on a computer.

bob_dallas

Another point - surface area can change with more folds/pleats. Remember the surface area of a filter does not = it's outside dimensions - you'd have to take off the frame and stretch out the filter element to get surface area.

rockitman

What I can say for sure is that the throttle response has improved dramatically...It is probably due to the less restrictive exhaust with larger pipe diameters in combination with the air filter. I did not have the BMC in prior to the exhaust, so I can't comment whether there is a pereceptible improvement in the throttle response time with the air filter alone. With both, I can say yes for sure on my car when I blip the throttle to match revs with wheel speed when downshifting. It is the only way I drive the car. I do not use gearing to slow the car, so by heal toeing correctly, you put less wear and tear on the clutch and tranny with the added benefit of no vehicle upset when down shifting prior to turn in under braking...

bob_dallas

OK, not trying to nitpick but this jumped out at me - are you serious? never engine brake? and you always heel and toe? You must be braking pretty damn hard on the roads because if I downshift at high enough revs to really blip (becomes moot at low revs) then the engine is definitely braking. I heel & toe with every downshift but I also end up using engine braking a lot as I'm slowing down for stop signs and lights - pretty much unavoidable unless you are braking very hard IMO.

rockitman

Your not nickpicking Bob...In most circumstances when I drive on the road, I try to avoid engine braking...If you are driving very aggressively and braking late, of course there will be some engine braking...Keep in mind when I drive on the street, while I may be aggressive and go fast, I don't even remotely challenge the limit in the turns...I start braking very early so that when I do come up to the turn, I am going relatively slow enough that I don't need to engine brake and focus on a turnin speed that will allow me to safely and smoothly accelerate through the turn so that my exit speed is greater than my entry speed...The whole purpose of my driving style is to work on smoothness and technique (practice) and picking the correct line so that after turnin I hit the apex at the inside of the turn and track out towards the outside of the turn while at the same time not having to adjust the steering wheel (the perfect turn...). This is of course not the same as on the track since I need to stay on my side of the road...but is good practice none the less. This is all preparation for when I finally make it to my first DE (get my 1st addictive fix... :-) ) and will make it easier to focus on brake points and turnin without have to think about proper shifting technique and rev matching...So yes, I do heal toe all of the time for it's more difficult under light braking than it is under a full step on the brakes...Call me crazy and please feel free to point out if I have got it all wrong, but I feel that I am working on the correct fundementals to make my transition to the track, a better one...

Bob Rouleau

jgerken - nice post. Thanks I could not have said it better.

Philip in AL - oooh, you opened a real can of worms! It's not about ramming air into the engine. Unless you have a turbo, the air is sucked in by the motor. The amount of air sucked in is a function of the displacement of the engine and the number of revs per minute. Low revs, low air pulled in, higher revs means more air.

At low engine speeds the motor does not need much air and can't suck in much. For example at 3000 RPM the engine will pull in half as much air as at 6000 RPM.

As long as the engine can suck in enough air to satisfy its needs, the filter doesn't matter. Say that a GT3 motor needs 800 CFM of air at 8000 RPM, as long as the air filter can supply that much, it has done its job. Replacing it with a filter than can pass 1600 CFM won't change anything, the engine will suck in 800 CFM only, it can't pull in any more unless you make the engine larger or increase the revs.

That fact is usually ignored by the guys selling high performance filters. It is also why Bruce Andersen discovered no power increase when he removed the air filter entirely - his air filter was capable of supply all the air the engine could pull in and reducing the restriction resulted in no extra airflow.

By the way I am not a K&N basher, I use them on my dirt bike and my daily driver. I do not believe that they add performance though. Like on the 993 most often the bottleneck is not the air filter but the air box itself which may have all sorts of sound deadening traps and bends.

Sean

I have a BMC on my Boxster S. I agree that it probably offers no statistically significant performance gain, but the improvement in intake sound is VERY noticeable. I have swapped back and forth between the paper and BMC filter, and the BMC makes for a vastly improved sound at wide open throttle.

bob_dallas

Nah - I'll drop this one because any practice is good on heel and toe IMO. If you do it every day it will make it easier on the track. It's not exactly easier under full braking because you have a few other things to think about and it needs to be very smooth but your daily practice should help it become second nature. Big blips, little blips, your brain needs to get trained how to match revs differently at different speeds without looking at the speedometer - it comes over time. You'll discover a whole new world when you get on the track - I'm sure you'll have a great time.