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Old 3rd March 2004, 11:49   #1
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Default What's a free flow exhaust ?

Hi there

Since i had a tecnhinal query, thought let me the first one to broach this topic in this (yet)virgin area of this message board

Have been hearing this term quite often offlate. Does anyone have any idea what exactly is it all about and what benefits can one expect after fitting it to the car ? Also can it be fitted on both carb as well as MPFI cars ?

cheers

aditya
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Old 3rd March 2004, 13:23   #2
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Hey guys,

Im gonna try and explain this keeping it simple.....correct me if there are any discrepancies

The exhaust system of a car takes the exhaust from the cylinders to the end of the tailpipe where it is expelled.

Starting off at the exhaust manifold which combines the individual exhaust gasses from the cylinders,


That pipe leads to the catalytic converter, which causes chemical reactions with the exhaust gasses to make them more enviormentally friendly

read this for further cat-con info > All Catalytic Converters - What Does A Catalytic Converter Do?

The output gas goes down a pipe to the muffler(silencer) which is required for cars to meet the noise pollution standards


Well that is a basic stock exhaust sytem.

Now what you have to understand is that even though we are dealing with gasses, there is still a good deal of pressure involved. Specifically backpressure. That is, the exhaust gas newly expunged from the cylinder has to push all the other exhaust through the manifold>pipe>cat>pipe>silencer. This is where the back pressure comes in, it provides a certain resistance.

A free flow exhaust, simply put, is an exhaust that decreases the amount of back pressure in the exhaust system and possibly also providing a smoother passage for the exhaust.

In my opinion, a free flow can have any/all of the following. A new exhaust manifold, providing smooth and equal length sections of pipe for gas from each cylinder (like the one in the first pic).
(Porting and polishing the head also helps the flow of the intake/exhaust gasses and is a mod, though not part of a free flow)

Pipes can be widened allowing more gas to flow. But keep in mind that theres always a right balance and backpressure seems to have its advantages.

The cat can be modified or removed all together. For example a certain evo6 in bombay was running without the cat at the autocar speedrun.

And the muffler aka silencer. This is where the most confusion can happen. Sometimes all you have to do is poke a hole in your silencer to make your car sound like its free-flowed. Its quite possible that 70% of the "freeflow" cars you see on our streets are actually just modded mufflers, giving the noise an the "feel" but no real benefit.

Importantly, keep in mind that huge amounts of research go into making a good exhaust system, its not just as simple as putting larger pipes and taking off the cat. Sometimes it can have a negative effect on the performance of the car.

As u must have figured, this can be done on carbed as well as mpfi cars.

After free-flowing your car, the gasses flow diffferently and hence your carb should be re-calibrated. And i can only assume that the correctway to do it with an mpfi is to re-program the chip ......(im not sure if there are enough sensors to calculate and adapt to the difference).

A good example of this is when your muffler cracks/rotts/falls off you will notice that your car starts to idle a lot faster (due to less back pressure)...

Hope i have managed to successfully convey this concept.
Let us know if you want to get further into this!

cheers
rehaan.

Last edited by Rehaan : 31st October 2007 at 00:11. Reason: fixed a few image links...
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Old 3rd March 2004, 13:29   #3
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Aditya,

Any internal combustion engine has a typical breathing sequence. Cylinders have intake and exhaust valves for precisely this purpose. While the intake valves will "breathe" in oxygen and mix it with fuel, combustion related waste gases are let out through the exhaust valves. Thus in a four stroke engine (typically the norm today), the engine creates most of its power during the "power stroke" and in the exhaust stroke, the exhaust valves open up for the piston to push the exhaust gases out of the cylinder.

While filters like the K&N typically help the engine "inhale" more efficiently, free flowing exhausts help an engine "exhale" better. Free flowing exhausts of good quality (both in parts and installation) help an engine breathe better by reducing the back pressure.

Simply put, interpret it as "free flowing" and you will get what the purpose is.

Hope that helps,

GTO
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Old 3rd March 2004, 13:39   #4
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So does that mean the faster the exhaust gasses are released out of the car, the better it performs?

I even hear than doing this not only improves performance but, also the fuel efficiency of the car.

Regards...
Shan2nu
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Old 3rd March 2004, 13:50   #5
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Yeah Shantanu free flows do enhance the performance of the car but Im not so sure bout the fuel efficiency

Cheers
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Old 3rd March 2004, 14:12   #6
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Mar. 03 2004,12:09)]So does that mean the faster the exhaust gasses are released out of the car, the better it performs?

I even hear than doing this not only improves performance but, also the fuel efficiency of the car.

Regards...
Shan2nu
Not necessarily Shantanu. It all depends on what performance means to you i.e. It is highly subjective.

I know of some guys who installed headers et all, but came away disappointed because the pipes they used were really wide. Even though performance significantly improved in the high end, their cars totally lost low end grunt. A big problem in city driving and practicality.

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Old 3rd March 2004, 14:25   #7
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Thanks guys..especially rehaan for making it so illustrative et al ..couldn't have been more simpler

cheers

aditya
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Old 3rd March 2004, 16:09   #8
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Yeah Rehaan,
Your presentation was A1.

Rehaans "N-PSY-CLO-PEDIA"

BTW did yo'll read Dippy's new book titled "How To Hate A Hyundai" lol

No offence Dip but, i love doing that to you

Kya karen, control hi nahin hota

Regards...
Shan2nu
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Old 3rd March 2004, 16:14   #9
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Hey Shantanu

Great idea My book will be called " 101 and more ways to hate a Hyundai"

Cheers
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Old 19th March 2004, 08:38   #10
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Dippy when you are going to release the book ?
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Old 19th March 2004, 09:13   #11
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Hahahaha....Dippy, this is like the 3rd time toyota has asked!! looks like it might just be a bestseller!

cheers
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Old 14th July 2004, 15:17   #12
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This is from an article in Overdrive November 2001.,which cud help u knowing more about a free flow exhaust.

One of the easiet ways of increasing the performance of a car engine is playing around with the exhaust gases.
Getting down to the basics ,tuning an exhaust is not a piece of cake,but that also does not mean u need a rocket scientist to do it .lets start from the beginning---
What is an exhaust system ?exhaust systems carry out several functions.among them are .getting hot noxious exhaust gases from the engine to a place away from the passenger compartment ,significantly reducing noise output from the engineand in the case of modern cars ,to reduce the exhaust emissions or to reduce our PUC readings.
After ur air -fuel mixture (or nitrous –fuel mixture)burne,u will have a bunch of leftovers consisting of a few inburned hydrocarbons(fuel),carbon monoxide,carbon dioxide,NOX ,SO2,phosphorous and the occasional molecule of a heavy metal.these are all in gaseous form and r under a lot pf pressure as the piston pushes them out of the cylinder and into the exhaust manifold is usually made of cast iron and its primary use is to funnel several exahsut ports into one,so u don’t need 4 exhaust pipes sticking out of ur 4 cylinder car.
But exhaust manifolds are pretty restrictive to the flow of exhaust gases and so a lot of power is wasted as ur pistons have to push these exhaust gases pretty hard to throw them out.In a four cylinder car ,there are 4 cylinders sharing the same exhaust manifold.the manifold can also be an important source of back pressure because exhaust gases from one cylinder builds up pressure in the manifold that affects the next cylinder that uses the manifold.
This back pressure develops a resistance that the piston faces to force the exhaust gasses out and in a way a good way for an engine to loose power.
Then why do almost all new automobiles sold have exhaust manifolds.that is because they are cheap to produce and easy to install.
The performance alternative to the exhaust manifold is using HEADERS.instead of a common manifold for all the cylinders,each cylinder gets its own exhaust pipe.these pipes come together in a collector,which is made up of two individual tracts .the individual pipes are cut and bent so that each one is the same length as the other.this guarantees that each cylinder’s exhaust gas arrive at the collector spaced out equally so that there is no back pressure generated by the cylinders sharing the collector .

To gain a more complete understanding of how headers do their job ,v have to understand what an’ exhaust pulse’ is.
Exhaust gas does not come out of the engine in a continous stream.since exhaust valves open and close .exhaust gases will flow the stop and the flow as the valce opens.for a ‘pulse ‘to move,the leading edge must be of a higher pressure than the surrounding atmosphere.
The ‘body’ of a pulse is very close to ambient pressure and the tail end of the pulse is lower than ambient.so in fact there is a complete vacuum.the pressure differential is wat keeps a pulse moving.
A header does a good job of additionally ‘sucking’ more exhaust from the engine combustion chamber ,so on the next intake there is more fresh air to burn.
Headers with smaller ,longer primaries will give a better economy and better drivability. whereas one with smaller length primaries and karger primaries will high revving
From the headers ,the exhaust gases flow to the cat con .there is some debate on whether removing the cat con will liberate some horse power.the cat con cleans up some of the harmful chemicals from the exhaust .also they do a neat job in modern cars in quitening up things.
From the cat con these gasses flow into the muffler .exhaust gases leave the engine under extremely high pressure .if these were let out directly into the atmosphere they make sounds like gunshots,that wud make u and others deaf within a minute.
A muffler that makes ‘horsepower’ is absolute crap.or some dodo mechanics defunct mind.in reality the best mufflers are no mufflers at all!!
Inside a muffler u will find a deceptively simple set of tubes with holes in them.these tubes and chambers are fine tuned as a musical instrument.they aree designed to reflect the sound waves produced by the engine in such a way that they partially cancel each other.

So I think this is enough to make u understand wat exactly a free flow system consists of.

Ever since I got a free flow for my car ,I have stopped using my AC when I am driving alone.it has turned me into a real maniac without caring for economy as I have to indulge in pulling through each gear.
The roar at 100-120 kph is superb .inside tunnels u feel as if u r in a F1 car.
So if u r going for a free flow make sure that u go to someone who knows his job .
Also simply changing the muffler will not give any performance benefits.
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Old 14th July 2004, 16:01   #13
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cooooooooo...cant wait to get mine!! just ordered it yesterday. sat with the guy whos making it (RAC bangalore) for me and went through the software they use for measurements etc..
hoping to have it by next the next weekend. test drove a 1.2 palio (mine is a 1.2 as well) in which they had already installed one. sounds lovely and the car responds a lot quicker.
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Old 14th July 2004, 16:47   #14
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Quote:
Originally Posted by [b
Quote[/b] (anoops @ July 14 2004,14:31)]
Hey Anoop.
Can I get their address or telephone number?
How much they're charging you?
Rudra.
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Old 14th July 2004, 18:30   #15
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hi
has any one seen a diesel car with a free flow ?? ...i have never...maybe the sound coming out frm a diesel car with a freeflow would be devastating...
cherio
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