Seems like all the issues people have with CAIs come down to the awful oiled cotton or foam filters they use.

Is it really that hard to redesign the intake for better flow, but use a decent filter? Or maybe the filter would have to be as big as the engine lid to flow enough air while actually filtering out particles.

 

The 996 already has the intake receiving air from directly outside the vehicle. This is what others selling CAIs are trying to acheive. The stock paper filter has a very large surface area already and is housed in a large air box. There is most likely already a ram air effect, as air moving over the car is directed into the louvers on the rear deck and directly into the air intake. This happens to even a greater degree when the spoiler is raised. At speed, the air box may even have positive pressure from its design. It's hard to improve on that. Oiled gauze and foam filters and the subsequent housings and plumbing, will generally offer more intake noise and the ability to clean the filter element.

As the stock system is dynamic by design, flow will improve with increased air movement across the car. It may be easy to improve torque output numbers on a dyno with less restrictive filter media installed. But these numbers generated in a static enviroment have little real world meaning. In the interest of performance, a study should be done of the intake and exhaust system. It should be determined what components generate the greatest restriction or barriers to increased air flow at both ends. Once they have been identified, addressed and corrected, move on to the next item. When everything external of the motor has been corrected, internal modifications are the the only thing left.

By just bolting on a different filter or exhaust header, you have little chance of making more usable torque in the rpm range that will make the car accelerate faster. This is especially true of a world class performance car like the Porsche. It's important to remember that peak numbers on a dyno mean very little. Lastly, it's pretty easy for Porsche to design an intake and exhaust system that will maximize power
generated by their motors. You're perspective may vary.

 

Beautifully written....

 

indeed!

 

But speculative and a little bit misleading.

Engine design isn't a more power/less power kind of process. That's naive. What we're talking about here - with everything from chips to intakes to exhaust modifications - is tuning. The statement that these mods won't produce more torque is likely often true, but it ignores the fact that a lot of performance tuning for cars like this isn't directed at drag racing. Often, the very mods that give you more peak power will make the car feel slower at normal speeds, but give you in exchange the ability to continue accelerating into the wall of wind at higher speeds... which is what horsepower is for. For some people, moving the power around the rpm band, which is what a lot of tuning does, has a purpose and is worthwhile.

Mods like this don't make a car better. They make it different. With all due respect, people who justify their mods with peak HP gains - unless they're racing - wasted their money, and reveal a limited understanding of what tuning is about. They're just bench racing. And I feel the same way about people who dismiss these mods on the same basis. They're just numbers. The only question that matters is whether the car is better for your purposes when the mods are done.

 

I agree. I tend to think what you get in HP you loose in Torque.

I changed my exhaust for the sound.

Changed my cats with less restrictive ones for the durability since my car runs rich and the more restrictive cats don't last for more then a year.

I tried the Evo airbox not sure if it does as good as a job as the OEM airbox. Compromising more air flow but for air that is not as clean. I like that it magnifies the noise from the engine compartment.

I have installed X51 headers, if it's good for the same engine then I couln't see it hurting anything.
Didn't notice any performance gain at all but it did change the exhaust note. Has a little more lower tone, almost a tad quieter.

 

Several points seem to come up in these conversations again and again. I won't bother rehashing all of the previous explanations. I think Bruce summed it up pretty well.

For those concerned about cleanliness, I agree that oiled cotton doesn't seem to filter as well as some other medias. That said, I've tested the oil on three different vehicles all running oiled cotton filters and have never seen elevated levels of silicon. This is a small sample size and not the be all and end all of tests, but it's enough comfort to allow me to sleep at night.

The factory airbox is good and does have a big filter, but if you've looked at the box design you can see that most of the filter isn't being used. Not because it's plenty big enough, but because the flow path of air is restricted by the resonance chamber.

After the fitment issues i had with the EVOMS I wanted nothing more than to see no gains with it so I could take it out of the car. Instead i saw a modest gain across a large part of the rpm band.

To answer the earlier question on efficiency calculations: I measured air flow using the stock MAF. You can calculate the theoretical maximum flowrate of the engine (displacement, rpm) and compare the numbers to determine the efficiency.

 

My intent was not to mislead, it was solely to offer a perspective.

I'm not sure what you mean regarding engine design. Engineers design motors with different objectives in mind. Some are designed with power as a main objective, others with fuel economy, still others with extreme low rpm torque. All of this is after certain reliability and environmental concerns have been addressed. Even if a motor is designed for a specific task, it is still "one size fits all" and can usually be improved upon.

I always regarded tuning as a way to taylor desired characteristics to better suit ones driving style. This can be in the area of torque and power management with motor mods and gearing, braking improvements and suspension setup. Ergomomics are important as well.

Your reply is confusing me. Horsepower is torque achieved in a certain amount of time. Increasing horsepower is achieving a given torque value faster, or increasing torque in a given amount of time. Any improvement you can do to maximize the twisting force in less time will give you faster acceleration thru an increase in horsepower. Any improvement that will maximize acceleration thru the first 3 gears and a bit into the 4th such as in the first quarter mile, should continue to improve acceleration all the way thru 4th, 5th and thru 6th gear. So, not trying to confuse, just state that any improvement verified by quarter mile times should carry over into the 100 mph to top speed territory as well.

My point is that too much creedence is put on peak dyno numbers, mostly by those that understand little in the way of power deliverly. The peak number is usually just attained for a split second before a shift. The torque and power at the point the rpms drop to and beyond are much more important for maximum acceleration.



Anyway, bottom line is, all that matters is that the guy that pays the piper is happy. Big gains, little gains, no gains or losses, your preceptions are all that counts. It's a different story when racing, all the BS stops, lol.

 

Yes, engineers design engines with specific objectives in mind, it's true. But never are those objectives single-minded. I don't mean to split hairs, but I think that really understanding what an automotive engineer faces is a useful way to put this kind of debate in context.

Engineers work with imposed parameters: Emissions, fleet fuel economy regulations, noise, safety regulations, things like that.
They also work with discretionary parameters: Marketing (where, for example, they will design to a high peak HP number so as to make good ad copy... ask me how I know), price targets, liability concerns, stuff like that.
They also work with market acceptability parameters: Noise, vibration, harshness, throttle response, brake pedal feel (you'd be surprised at how many people hate a 'jumpy' throttle or brakes in focus groups), things like that.
And mechanical parameters: Reliability, durability with respect to warranty exposure, component cost, available existing platforms and shared components, production engineering (ie how it will be assembled), packaging under the hood, serviceability, maintenance intervals, that kind of thing.
And, finally, the intended use of the engine, where they will tip the bundle of compromises in the direction of low end torque for a truck, or high horsepower for a sports car, or quietness for a luxury car, or whatever.

Every single thing you see and experience in a car is a complex set of compromises that very likely got fought over right up to the time the line started rolling. Even the Veyron had to draw the line somewhere. One of the things we like about Porsches is that a lot of those compromises didn't get made, especially the ones dealing with the lowest common denominator consumer. They are simpler, more focused cars. But lots of trade-offs still happened, and this is especially true of the 996, which was designed and built when the company was in financial trouble.

In the years I worked with Toyota (and briefly with Honda), every powerplant engineering presentation I ever saw focused on the brilliant compromises they'd made. Good quality mods if they're well chosen, put some of the control over those compromises back in the owners' hands. He can choose different tradeoffs than the designers did on some of the less critical items.

To me, modding a car is a creative thing. With my car, for instance, I did the EVOMS intake and the EVOMS exhaust, a REVO custom flash and a B&M short shift kit, but my suspension rides on Bilstein HDs at stock North American height, yet has brilliant tires. It has no stability control or LSD, no nav, no nothing except a stereo and hard back sport seats (and console delete). If you drove my car, you would say that it has a distinct personality as a result. It's less civilized than a typical modern 911, and to me has a tiny bit of the character of an old one in that things feel and sound very immediate, but it's still a sports car rather than a race car. That suits my taste. The HDs are there because I want all four tires on the ground on real world lousy roads at the speeds I drive. I love the look of a lower, firmer suspension, but for my kind of driving it would be slower, not faster. I made it for me. I don't think my car is better or faster than anybody else's, and I'm more interested in the total effect of the mods than on any one item. I just changed the mix of compromises and personalized the car.

I don't mean to ramble on about this. But I really do believe that people have to leave a little room for guys to make what they want of their machines. Most of the naysaying about mods is pretty baseless, and you can't drive numbers anyway.

 

Bruce, of course, you are correct. I should not have stated in an "absolute manner." I should have stated that "HP gains will be minimal, if any."

It is just that I get so fed up with some of these aftermarket guys claiming a 10+ gain in HP with their "cold" air intake, when that "cold" air is coming directly from inside the "hot" engine bay.

The Porsche Carrera Power Kit costs $16,900 and adds 26 HP. That included modified cylinder heads, carbon-fiber air filter casing (upper part), new variable resonance intake manifold, sports exhaust system, and modified engine management. So the aftermarket claims that a $350 to $600 air intake alone will add 10+ HP is ludicrous. Even if a CAI did add 5 HP, on a MK II car with 320 HP that additional 5 HP is a 1.6% increase in power. Who would ever notice that?

Can anyone say that the stock air intake leaves the engine starving for air? The volume of air that moves through the stock intake is more than the engine needs if no additional changes are made to the engine.

Personally, I would NEVER add a CAI to any car I own, let alone a Porsche!

 

It's true. Marketers in this category don't do themselves any favours, unfortunately.

 

Bruce, thanks for adding all the gory details! I'm very aware of all of those things, just sometimes like to forget about them.

Glad to hear that you have done several things to your car to individualize it and make it your own. Sorry to hear that it's no better than anyone elses, lol. (I'm certain it is!)

 

I always wonder what additional changes were made to the car to allow them to get a proven XX HP gain. Their wording is such that it makes me wonder. Here is a good example. I changed the manufacturer name to XYZ:

"How does a XYZ air intake increase horsepower? It all stars with The World's Best Air Filter............ In fact, on the 2003 Ford Mustang SVT, XYZ engineers were able to achieve an impressive increase of 30 horsepower!"

The second sentence boasts that the engineers were able get 30 HP gain on a Mustang, but it doesn't say that the 30 HP gain was attributed only to the CAI.

It has been a long time since I got sucked into a CAI thread! No more!

I would rather debate oil!

 

I can be such a bore.

 

BruceP good shot at the dilema of airbox fiddling.

I just wish aperaceparts supplied parts and porting for the porsche. Then we would be talking real flow numbers. I just gave up and emailed them to see if they would work on porsche heads.