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Hi, would a cat back exhaust in conjunction with a WAI/CAI provide any noticable increase in power?. Could anyone explain me how do they work (cat backs)? are headers part of them?. Thanks
 

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No, your headers are not included in this package, as your headers are before your catalytic convertor.

It will be from your CAT back.

The advantage of these enhancements are to allow your engine to intake and expel gasses more freely.
The only fall back on this though is if you go to big in your exhaust, you will loose any back pressure, which will do you no favours except at around RPM where you do not usually drive your car all the time.

Back pressure, is the effect of the slight restriction caused within your exhaust system.
A high back pressure will lower engine power, however a really low back pressure will lower engine power low down in your rev range.

The correct back pressure in your exhaust should create a backpressure within your exhaust system that does not restrict engine output, but creates enough of a restriction for the exhaust gasses to travel quickly out of the exhaust due to the size of your pipe diameter.

eg, if you have a big pipe, then gases can expand and fill your exhaust pipe, and basically just come out of your exhaust pipe because it is the only place that they can come out.
But if your exhaust pipe provides a slight restriction, then as your exhaust gass enters your exhaust pipe, they cannot expand outwards, because your pipe diamtere restricts it from doing so, so they expand in the direction of the tail pipe, meaning that they are travelling quicker to your tail pipe, which provides a scavenging effect four your cylinders.

Petrol engines are by no means effecient. An atmo engine can not expel all of the gasses out of it cylinders on its own.]
So because your back pressure in yoour system is causing your gasses to expand and travel towards your tail pipe, behind each exhaust pulse their is a low pressure created, because your exhaust valve has closed but your exhaust gas is still moving toward your tail pipe due to expansion.
So when your next exhaust valve opens, the low pressure in the exhaust works with your high pressure in your cylinder, and essentially "sucks" out most of your exhaust gasses.
With a big exhaust pipe, there is not back pressure, therefore it cannot create a low pressure in the exhaust system! :)

Sorry for the message being so long guys, but at least if you know nothing about exhaust systems, at least you will know something now! :)
 

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You will probably see about 10-15hp with a full intake and exhaust set-up. Good write-up by the way, Dr. Hundi.
 

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Dr. Hundi made a point of mentioning that his explanation referred specifically to normally-aspirated "atmo" engines.

With a turbo or supercharged setup, the reverse is true & back-pressure needs to be eliminated completely.....hence the use of bigger bore, less restrictive systems.

Nick.
 

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True, however, no point was made of forced induction systems. But now that we are on the topic.

Performance exhaust systems on atmo engines can not even be compared to that of a forced induction system, these systems become two completely different components when refered to in these systems.

With a turbocahred system, you want as least as possible back pressure within the exhaust system.
Because of the effect of the turbocharger, the exhaust is in a way, "less crucial" to performance as that of a high powered Atmo system.

A turbocharged system relies on the low pressure created at the rear of the turbine wheel, to draw exhaust gasses from the combustion chamber, when the exhaust valve opens.
The wasted gasses are then basically pumped out by the action of the turbine wheel.

On an Atmo engine, the engine relies soley on the effect of scavenging to remove the wasted gasses from the combustion chamber.
The only way that this can be achieved to as close to 100% as possible, is to have the entire exhaust professionally designed to create the correct flow rate within your exhaust.
Exhaust gas comes out in pulses, whilst no1 cylinder expels its gasses, and flows down the header pipe, the exhaust valve then closes.
Behind this exhaust pulse there is now a low pressure area created by the movement of gasses from a closed off area.
What a perfect exhaust system should try to achieve is this:

The low pressure that is created within the exhaust system is at the head of the valve, however because of physics, the gas continues to expand and travel in the outward position, continuing to create a lower pressure within the header area, at the valve.
What you want is for your low pressure amount to refrain from reaching really low pressures, because this slows down exhaust gas flow, but ultimately you want enough low pressure for when the gas pulse reaches the collector area (where all your pipes meet together), and the next valve has opened, this low pressure draws out most of your exhaust gas.

The problem created when trying to achieve such a high efficiency of exhaust on an Atmo engine, is that in trying to manufacture an exhaust design that allows a good scavenging effect to take place, you will always run into the problem of ... Backpressure anyway, but just not as much.

And if you want to get really technical there is even exhaust back pressure within a turbocharged system!!! :blink:
:) :)
 

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& us turbo guys do our level best to get rid of it!.

Nick. ;)
 
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