Performance panel filter or CAI? Tell us what you use

[Antiplastix]

Isn't that grid / louvre there to straighten out turbulent air flow?

Dont know, but it makes better induction noises with it gone. It seems marginaly more responsive, but that could be a placebo effect from the nicer sound.

[BottomScratcher]

My Carbonio sounds great, and so does my 3" catback... If those are the only gains I've gotten from upgrading both ends of piping - then sobeit!
I think I can live with that.
Of course, I'm not speaking for everybody with that piece of text - but I'm sure that it counts for a fair few.

Fair enough too mate. I didn't mean to sound judgmental. I just find it hard to ignore the physics. When I said "useful" I was solely referring to performance, i.e. increased horsepower at the drive wheels. If you're satisfied that it looks cool, sounds great, or whatever else about it blows your hair back, then that's all that matters, and whatever I think is worth as much as I get paid for writing this.

[Weekend-Warrior]

Goes to what I said about the 440ml can of Guinness and the 425ml schooner glass...

You're neglecting a few things, some being pressure and density. You're comparing volume. That's different to pressure and density. And you're comparing a liquid to a gas. Liquids are pretty hard to compress.

With a restrictive intake you have a larger pressure drop than if the intake was less restrictive. With a pressure drop you have less dense air (than atmospheric) entering the cylinders. Bolting on a turbo helps over come this, but you'll see improvements by reducing the pressure drop.

Changing the intake by changing the filter, removing bends, resonators, etc, should reduce the pressure drop, therefore increasing air density which allows for more fuel, equals bigger bang, more HP... and that may help blow your hair back.

[woofy]

You're neglecting a few things, some being pressure and density. You're comparing volume. That's different to pressure and density. And you're comparing a liquid to a gas. Liquids are pretty hard to compress.

With a restrictive intake you have a larger pressure drop than if the intake was less restrictive. With a pressure drop you have less dense air (than atmospheric) entering the cylinders. Bolting on a turbo helps over come this, but you'll see improvements by reducing the pressure drop.

Changing the intake by changing the filter, removing bends, resonators, etc, should reduce the pressure drop, therefore increasing air density which allows for more fuel, equals bigger bang, more HP... and that may help blow your hair back.

I guess the questions come down to:

A: Is the engine in these really air starved being turbo, ie will removing restrictions in the intake without looking after the exhaust or changing tune/fuel systems do much at all, or will it just cause more air over the MAF to cause the engine to inject more fuel for air that might not actually make it into the cylinder.

B: My current ponderings with CAIs only, is it just causing more hot air to come in when they are quite often routed to not so cold spots in our hotter climates. Especially with hot road temps. I've only ever seen back to back comparisons up away from the ground on a dyno in quite often nice cool workshops....Hard to test really.

[Weekend-Warrior]

A: Is the engine in these really air starved being turbo...

No, it's not being "starved". If it was you'd see a big dip in the power curve. However improvements can be made if you're happy to sacrifice noise levels. Reducing the restriction is pretty simple, hence you can buy bolt on kit to help extract a few more hp.

B: My current ponderings with CAIs only... is

Think of the CAI as more of a Free Flowing Intake. Most of the "CAI" I've seen for the Octavia stuck air from the same area as the standard intake. You could easily check whether there is a temperature difference 200mm off the road compared to 500mm. I think a good position with positive pressure would be better than the level off the road. You can easily measure the pressure drop so could do this pre-CAI and after to see what the difference is. And there are plenty of articles around that explore intake restrictions.

[Martin]

Hmmm, don't put too much weight on poll results
On an enthusiast forum like this, customisation and bling are reasons to buy rather than benefit
Often many people do the same wrong thing (Election voting, watching big brother, etc), the average of many thousands of poor decisions does not guide you towards a good decision

[BottomScratcher]

You're neglecting a few things, some being pressure and density. You're comparing volume. That's different to pressure and density. And you're comparing a liquid to a gas. Liquids are pretty hard to compress.

With a restrictive intake you have a larger pressure drop than if the intake was less restrictive. With a pressure drop you have less dense air (than atmospheric) entering the cylinders. Bolting on a turbo helps over come this, but you'll see improvements by reducing the pressure drop.

Changing the intake by changing the filter, removing bends, resonators, etc, should reduce the pressure drop, therefore increasing air density which allows for more fuel, equals bigger bang, more HP... and that may help blow your hair back.

I mentioned density, temperature, altitude, and maybe even humidity on previous posts. And I've definitely dealt with pressure, both in the intake system (turbo and supercharging), and in the cylinder. I used a liquid (Guinness) only as an example of how if the volume of a cylinder is constant, which it is, then the only way to satisfactorily increase the density of the air inside that cylinder is to turbo or supercharge.

Turbos are driven by the exhaust gases. If you've already got a turbo in your intake system increasing the airflow mass to the turbo isn't going to deliver any more air to the cylinders on the intake stroke. Even if you could eke a bit more denser air inside the turbo I suggest any such gain would be immediately lost when the air again rapidly expands in the intake manifold and cylinder after exiting the turbo. I understand what you're saying about minimizing airflow restrictions, but unless you're going to polish and port every component in the intake system, and get rid of the standard exhaust system I really wouldn't bother with trying to get performance gains from a panel filter, or a CAI that isn't insulated from engine bay heat.

[Weekend-Warrior]

Not trying to create a war but happy to point out some facts...

Ok so we agree density, temperature and altitude noticeably effects how an engine runs.

Density - more dense, more oxygen.
Temperature - colder, more dense, more oxygen
Altitude - closer to sea level, more dense, more oxygen.

So if all these things noticeably effect how an engine runs, why can't a restrictive intake which causes a pressure drop have the same effect?

I agree the swept capacity of the engine is constant, however density isn't. If density was you wouldn't need a MAF.

Turbocharging and supercharging are just two ways to cram in more oxygen. Different fuels, chemical injection and water injection are a few more.

Yes, it has a turbocharger, but if you're compressing air that's at less than atmospheric pressure the turbo needs to work harder to compress the air to the desired boost pressure which increases the temperature of the charged air. The laws of thermodynamics. Ideally you want the air at atmospheric pressure.

A centrifugal compressor works by converting velocity into pressure. It doesn't rapidly expand in the intake. The volume is constant like you say earlier, it's compressed.

So reducing the pressure drop helps, regardless of whether it has a turbo or some other way of increasing the oxygen content.

Like I posted earlier, agree an exhaust would probably have a larger effect. But there is a point to removing restrictions in the intake if you've looking for maximum hp. Polishing is another step which is much more costly than removing some plastic piping.

[Dutch77]

There's a few references in this thread to CAIs being or not being insulated from engine bay heat.. are we counting CAIs such as the Carbonio or the new VARDesign ones which use a sealed carbon box and only draw air from outside as sufficiently insulated or is a whole lot more insulating needed? Just curious..

[BottomScratcher]

QUOTE=Weekend-Warrior;921462]] A centrifugal compressor works by converting velocity into pressure. It doesn't rapidly expand in the intake. The volume is constant like you say earlier, it's compressed. So reducing the pressure drop helps, regardless of whether it has a turbo or some other way of increasing the oxygen content.[/QUOTE]

I'm not looking for a brawl either. I agree with most of what you say. The point above I don't. When I said the cylinder is a constant it's a constant twice in the combistion cycle. At the top of the piston stroke, and the bottom of the piston stroke. Whenever the piston is in motion between those points the cylinder capacity is a variable.

To assist expel the exhaust gases before the exhaust valve seats shut the intake valve starts to open to purge the cylinder - valve overlap. At that point with both intake and exhaust valves open, albiet for a very short time, the cylinder and intake manifold are open to atmospheric pressure via rhe exhaust system.

After the exhaust is expelled the piston travels down again as the exhaust valve shuts and the inlet valve opens further. With the inlet valve open and the piston creating a vacuum by displacement the cylinder capacity is variable as is the pressure in the cylinder. Air at near atmospheric pressure will be drawn to a lower pressure area. Any compressed gas entering an area of lower pressure than itself will expand. A compressed gas entering a vacuum will rapidly expand. A compressed gas entering a cylinder will expand as the piston travels downwards until the piston is at the bottom of its stroke.

I'll agree to disagree and remain unconvinced that as a stand alone performance mod that CAI's or panel filters are worth the money on an already turbo'd engine.