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Old 28th July 2011, 11:28   #121
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Default Re: What's a free flow exhaust ?

thanks Cyrus gypsy has been sold.i am asking for the ohc vtec. Just dont want loud sounds at lower rpms.
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Old 12th August 2011, 21:04   #122
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Default Re: What's a free flow exhaust ?

Hi,
Guess i'm a bit late to this party.

Went through every single post but some issues with FFEs were left out, so mentioning them here. Gurus please comment.

1. A free flow exhaust is said to improve fuel efficiency, as the engine doesn't have to pump out the gases and therefor runs with less load. Good for a theory, but does it really happen?
As far as i know, any engine runs with a 'Valve overlap period' according to the required operating condition/application. Valve overlap is the time when both intake and exhaust valve are open simultaneously nearing the end of exhaust stroke and lasting through a fraction of the intake stroke to aid in scavenging. The reason being the escaping gases 'pull' the fresh charge into the cylinders. in fact a well tuned free flow exhaust will utilize the resonant properties to make cylinder filling more efficient. the more fresh charge there is (ideally some exhaust gases are left in the chamber ) the more air and fuel to burn and hence better power. Ideally, the valve overlap is designed keeping in mind the exhaust back pressure. if a stock valve overlap period (read stock cam shaft) is used along a FFE system, won't the reduced back pressure allow more than necessary scavenging- that is the exhaust gases pulling the fresh charge to the exhaust manifold- which will introduce unburnt fuel into the exhaust manifold, and also reduce fuel efficiency, while increasing HC emissions?
[Although undoubtedly the problem would be less in magnitude as the revs increase, where the faster engine speed would nullify the effect due to the gases' inertia]
So would an FFE really improve FE during normal driving?? Have not used one yet. Gurus pls elaborate

2. Have heard of exhaust valves getting burnt in improperly designed systems. how is that possible?
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Old 17th August 2012, 12:40   #123
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Default Re: What's a free flow exhaust ?

I intend to buy an Accord V6 soon. How BENEFICIAL will a well engineered Automech exhaust be, in improving the performance?
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Old 17th August 2012, 13:38   #124
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Default Re: What's a free flow exhaust ?

Quote:
Originally Posted by dhawcash View Post
1. A free flow exhaust is said to improve fuel efficiency, as the engine doesn't have to pump out the gases and therefor runs with less load. Good for a theory, but does it really happen?
When my car had a cracked exhaust, I noticed that both performance and FE were better
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Old 17th August 2012, 15:05   #125
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Default Re: What's a free flow exhaust ?

Quote:
Originally Posted by Guna View Post
When my car had a cracked exhaust, I noticed that both performance and FE were better
Thanks for the reply.

In my honest opinion, a cracked exhaust only gives a psychological sensation of improved performance. (As an example, cruising at 100 on a highway with the windows closed may seem boring, but open the windows and the same speed becomes quiet action packed)

How much FE did you gain? did you change your driving style owing to the sportier sound ?

i still think this is just a marketing gimmick for free flow exhausts (claiming FE gains). From all i know about how an engine works, it does not make sense for a free flow exhaust to improve FE while retaining the stock cam.

Still waiting for better experienced BHPians thoughts on this. And i'd prefer numbers and scientific facts supporting the theory, as personal experiences cannot be quantified properly.

(Has been more than a year since any action on this thread)

Last edited by dhawcash : 17th August 2012 at 15:09.
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Old 17th August 2012, 15:49   #126
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Default Re: What's a free flow exhaust ?

Would like to share an experience:

Please note i may be contradicting my self a bit here. do bear with me.

In my college days, i used to have ample free time so decided to do some old school mods to my Bajaj Pulsar 180 Classic. It was decided that the head would be polished, and the stock exhaust modified to make it slightly freer flowing.

So i set about removing the exhaust and dismantling the head. Armed with various grades of heavy duty sandpaper and a lot of patience, set about making the exhaust port surface smooth (had ripples as it was made by casting). gradually, went from coarse to fine sandpaper and the port was as smooth as a baby's bottom. (no changes were made to the intake port for reasons out of the scope of this thread)
(sorry no pictures- did not have a camera with me in those days)

Next, came the exhaust's turn.

peeped down it, and noticed there was a ristrictor in the exhaust pipe. to explain without pictures, the exhaust pipe was say, 30 mm thick and the mouth of the pipe was only 27mm thick ( an orifice like structure). Being young and recently have read a lot about exhaust gas flow, i did not think twice before arming my self with a round file and getting rid of the orifice. i did my best to make sure the exhaust port outlet and exhaust pipe inlet diameters matched closely.

Assembled it all and went for a ride. the engine felt eager to rev (may be an illusion). Hit the highway and exercised the right wrist.

'What the !!!!' not much action! was at 2500 rpm when i floored it. 180 classic is known to have good grunt and the bike felt to have lost its punch. still accelerated though. as i reached 5500 rpm, i got the punch which earlier used to come at 2500-3000 rpm. went like stink from 6000 rpm onwards (while vibrating like hell- 180s are no smoothies) The torque band had shifted!

Now i have no on paper data, or any other means to prove it except my words (The reason i mentioned i'll be contradicting my self in the beginning- i did not quantify the experiment)

The results made sense. i had got better flow by eliminating the orifice and polishing the head. This reduced the back pressure, and the optimum valve timing now came at higher revs.

Lost the mid range because fresh air fuel mix was getting into the exhaust during the valve overlap period, and cylinder filling was less efficient.

and when ridden normally, and did not notice any major changes in the FE.
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Old 17th August 2012, 15:49   #127
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Quote:
Originally Posted by frankmehta
I intend to buy an Accord V6 soon. How BENEFICIAL will a well engineered Automech exhaust be, in improving the performance?
How do you know it is well engineered ? A proper ffe has to be designed on a flow bench. I doubt any aftermarket guys here have one. Get the headers from a branded company from USA. And the rest from one of the local guys. Obviously this will cost more.
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Old 24th March 2013, 22:09   #128
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Default Re: What's a free flow exhaust ?

Is it possible to get a free flow installed for improving performance without increase in sound? I like my car to be silent and it is the main reason keeping me away from free flow exhaust.
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Old 25th March 2013, 11:32   #129
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Default Re: What's a free flow exhaust ?

Quote:
Originally Posted by PatienceWins View Post
Is it possible to get a free flow installed for improving performance without increase in sound? I like my car to be silent and it is the main reason keeping me away from free flow exhaust.
One of the functions of a stock exhaust system is minimizing the exhaust sound to the minimum by the use of mufflers and baffels which cancels the sound waves.
On FFE, its called 'free', because there is nothing in it to block or reduce the sound waves,(and of course the flow of exhaust gases ), except for glasswool. In other words, getting the stock silence on a FFE is difficult.

You can get a FFE made with minimum sound output which is done by stuffing as much as glasswool as possible to absorb the flat sound waves which leaves you with the boom(bass) which will be heard only at revs close 3000rpm, im referring to 1.2-1.3 engines.
Reverse cones are also fitted in some cases to further reduce sound which may or may not affect the performace.
Below these revs, its almost as good as a stock exhaust system when it comes to the sound.

Last edited by tharian : 25th March 2013 at 11:37.
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Old 16th June 2013, 13:33   #130
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Default Re: What's a free flow exhaust ?

Hi All,

I couldn't find any information about this through my search on tbhp. Mods please move this post to correct thread if I am posting it i a wrong thread. I have a polo 1.6 and the engine is very sluggish and I thought going with the basic mods i.e. a CAI and FFE will add that extra punch which is required. However, one question about FFE which I would like to ask is the O2 sensor. In Polo the O2 sensor is placed at the conjunction of all the 4 pipes coming from the cylinders. Now if I choose to go for FFE with 4X2X1 where would the O2 sensor be put. A lot of people mentioned that for them it was placed on 2nd cylinder or 1st cylinder, but thats not the right way of doing it. Is it? As that would cause some cylinders to run lean/ rich. Also if I put the same at the cross section where are the 4 exhaust pipes meet then will it not be too far from the cylinders, as the O2 sensor works on the exhaust gas temperature to trigger a voltage. Also, after installing FFE what will happen to the pollution check which I have to get done in Delhi, would that be hampered? Not really sure if my facts are correct here, but some guidance would be great. Also, please guide which FFE is the best, and where can I get it done in Delhi?
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Old 16th June 2013, 13:51   #131
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Default Re: What's a free flow exhaust ?

Quote:
Originally Posted by shelleve View Post
Hi All,

I couldn't find any information about this through my search on tbhp. Mods please move this post to correct thread if I am posting it i a wrong thread. I have a polo 1.6 and the engine is very sluggish and I thought going with the basic mods i.e. a CAI and FFE will add that extra punch which is required. However, one question about FFE which I would like to ask is the O2 sensor. In Polo the O2 sensor is placed at the conjunction of all the 4 pipes coming from the cylinders. Now if I choose to go for FFE with 4X2X1 where would the O2 sensor be put. A lot of people mentioned that for them it was placed on 2nd cylinder or 1st cylinder, but thats not the right way of doing it. Is it? As that would cause some cylinders to run lean/ rich. Also if I put the same at the cross section where are the 4 exhaust pipes meet then will it not be too far from the cylinders, as the O2 sensor works on the exhaust gas temperature to trigger a voltage. Also, after installing FFE what will happen to the pollution check which I have to get done in Delhi, would that be hampered? Not really sure if my facts are correct here, but some guidance would be great.
Its best if the O2 sensor cable is lengthened and the sensor located such that it reads from atleast 2 if not not all 4 cylinders.

In my Swift the car ran better when the sensor was moved from its position on a single runner to a location it got to read two cylinders.

I assume that your Polo has got a heated O2 sensor, so it is not dependent on the exhaust gas to keep it hot to keep itself clean and so you don't need to keep it close to the head. Voltage generated in the sensor is dependent on the amount of O2 in the exhaust.
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Old 16th June 2013, 19:35   #132
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Default Re: What's a free flow exhaust ?

Thanks Sankar. How do you extend the car's O2 sensor to read from two cylinders? Also, what about the pollution check, as the FFE would remove catalytic converter. Also, can you recommend anyone from Delhi who does FFE's?
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Old 16th June 2013, 22:06   #133
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Default Re: What's a free flow exhaust ?

Quote:
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Thanks Sankar. How do you extend the car's O2 sensor to read from two cylinders? Also, what about the pollution check, as the FFE would remove catalytic converter. Also, can you recommend anyone from Delhi who does FFE's?
The O2 sensor bung should be located after the 1st or 2nd collector in a 4-2-1 pipe. If placed after the 1st collector the sensor reads from 2 cylinders and if placed after 2nd collector it'll read from all 4 cylinders. Once the location of the bung is finalised all 4 (or 5) wires of the O2 sensor needs to be extended so that the sensor can be screwed into the bung and the wire reach the socket in the wiring harness. Use same guage wires for extension and solder and heatshrink tube the joint for reliability.

No idea reg anyone from Delhi for this job, but you might find some info in the tuner directory.
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Old 16th June 2013, 23:11   #134
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Quote:
Originally Posted by shelleve View Post
Thanks Sankar. How do you extend the car's O2 sensor to read from two cylinders? Also, what about the pollution check, as the FFE would remove catalytic converter. Also, can you recommend anyone from Delhi who does FFE's?
Pollution checks are a breeze, no issues with the ffe even. And this was with my Santro which was 60k old when I got the exhaust done.

As for Delhi ffe guys, if you know exactly what you want, go to the guys behind scindia house on kg marg, they are willing to be directed by owners, or you can try the directory here for some known houses.
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Old 17th June 2013, 14:57   #135
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Default Re: What's a free flow exhaust ?

Thanks Mayankk and Sankar.
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