Manifold - Saxperience

srcnix · 15th November 2006, 12:56

I'm really wanting to understand more about cars so as off now I am going to ask some questions regarding cars. Some of the questions may be obvious but please bare in mind I am asking as I want to learn, not for people to rip the shit out of me

Anyway, first question. What's with the 4-2-1 manifold? I am guessing that the manifold is what connects the engine to the exhaust, or am I wrong?

I am then guessing that the 4-2-1 represents the pipes going from 4, to a two pipe to the final back box (1) ?

I may have this totally wrong but feel free to explain.

uppitysi · 15th November 2006, 13:05

spot on mate

Mystic^p · 15th November 2006, 13:17

Manifold = 4 pipes come out of the engine and merge into a single pipe by the time they are underneath the engine. Either merging as you said, 4 into 2 and then the 2 into 1 Or another variant is 4 all into 1.

Then you have a catalytic converter as close to the manifold as possible, followed by the centre section of the exhuast and then into the backbox.

It varies from car to car, even from saxo to saxo but thats a rough idea

S34MER · 15th November 2006, 13:48

4-2-1 manifold looks like this

and as you can see from your descrition, your bang on mate!

there is also another one called a 4-1 manifold, yep you've guessed it, it just goes from 4 pipes to 1 lol! here.....

srcnix · 15th November 2006, 13:53

Thanks guys, I guess this leads me onto two more questions:

1. Mystic, what is a catalytic converter?

2. What are the benefits of a 4-2-1 over a 4-1 ?

S34MER · 15th November 2006, 14:00

1. My names not Mystic, but i'll answer for you. There are millions of cars on the road that are potential sources of air pollution. In a major effort to reduce vehicle emissions, carmakers have developed an interesting device called a catalytic converter, which treats the exhaust before it leaves the car and removes a lot of the pollution.

2. In many cases 4-into-1 headers are designed for racing applications where the vehicle is being driven at or near redline during competition. The 4-into-1 design maximizes top end power, whereas the 4-2-1 evenly distributes power throughout the power band. There are cases where a 4-into-1 header works better than the 4-2-1, and in those cases we will only manufacture a 4-into-1 design.

srcnix · 15th November 2006, 14:02

Thanks S34MER, rep given previously.

Mystic^p · 15th November 2006, 14:03

1) Well since the engine combusts fuel and air mixes, there are other chemicals which are given out. I think Carbon monoxide is the main one. So the catalytic converter contains some material which is suppose to neutralise some of these poisonus gases to make the car run more environmentally friendly.

2) the standard manifolds are quite restrictive and generally contrain a join between the manifold and the downpipe.

A 4-2-1 offers more power in your lower revs and a 4-1 offers more power higher up. Idealy both of thises will include the downpipe and therefor not have the join.

I think thats about right anyway

srcnix · 15th November 2006, 14:10

Are you able to explain why it is that a 4-2-1 gives higher power at lower revs and a 4-1 gives higher power at higher revs?

srcnix · 15th November 2006, 14:10

Quote:

Originally Posted by Mystic

1) Well since the engine combusts fuel and air mixes, there are other chemicals which are given out. I think Carbon monoxide is the main one. So the catalytic converter contains some material which is suppose to neutralise some of these poisonus gases to make the car run more environmentally friendly.

2) the standard manifolds are quite restrictive and generally contrain a join between the manifold and the downpipe.

A 4-2-1 offers more power in your lower revs and a 4-1 offers more power higher up. Idealy both of thises will include the downpipe and therefor not have the join.

I think thats about right anyway

Thanks for the information Mystic. Much appreciated.

Mystic^p · 15th November 2006, 14:25

Quote:

Originally Posted by srcnix

Are you able to explain why it is that a 4-2-1 gives higher power at lower revs and a 4-1 gives higher power at higher revs?

I think the answer to that would be pretty technical and probably not worth your time trying to understand.

There are a few good site you can read through for general information on car engines etc.

http://www.carbibles.com
http://www.gmcmotorsport.co.uk - They go quite in depth about their choices of products, its also tailored to saxos
http://auto.howstuffworks.com/
http://en.wikipedia.org/

srcnix · 15th November 2006, 14:26

Thanks Mystic.

Mystic^p · 15th November 2006, 14:29

Nps, gotta start somewhere

Scott^p · 15th November 2006, 16:08

further manifold and car info @ www.gmcmotorsport.co.uk

srcnix · 15th November 2006, 16:09

Do Saxos have 4-2-1 or 4-2? Seen around lately with people stating how they're getting 4-2-1 so I get the impression they're 4-2.

srcnix · 15th November 2006, 16:10

Quote:

Originally Posted by Scott

further manifold and car info @ www.gmcmotorsport.co.uk

Thanks Scott.

piperX · 15th November 2006, 22:25

what happens with the 4-2-1 is all to do with pressure, the air in the four pipes get compressed into two pipes, so the pressure is doubled - meaning the air is pushed out faster, then it is compressed again into one pipe, so the pressure is doubled yet again, thus pushing the exhaust gases out faster, which overall allows the engine to burn more fuel giving maximum power.

srcnix · 16th November 2006, 09:08

Right ok, am I right in saying the more the air is compressed the higher the power at lower revs? Because the exhaust gas is getting out faster?

Where as with a 4-1 there is more noticeable power towards the higher revs because it is leveled out (As there is no 2 pipes to go through so the power is pretty level all the way through) ?

Many questions I know but I would like to understand this. I have read some articles but nothing that explains why 4-2-1 gives more power at lower revs compared to 4-1 where the power is at the higher revs -- at least how Mystic explained it to me.

S34MER · 16th November 2006, 09:50

You really anna know

Ok, this is gonna take a while to explain, so grab a coffee put your feet up and relax! Ok, as i already explained, many things are said about the merits of 4-2-1 as compared to 4-1 as to the performance properties each has.
The basic facts are that a 4-2-1 will give more low down power at the expense of a bit of top end and the 4-1 is the opposite, slightly less bottom end but more top. The problem for someone choosing which manifold to buy are not as simple as this, as the above comments are based on the manifold being built to set physics principals, that do not change, no matter who has built it.
The principals are too complex to go into fully, so below are the basics.
When you burn

the fuel and it escapes from the exhaust valve is has a pressure wave, this wave has energy and it can be harnessed to suck more gas than normal from the cylinder, this is the reason for performance manifolds. These waves have a natural harmonics and pulses and you have to get these right to make them do their job. To their job the exhaust pipe diameter has to be correct and more importantly the length of the pipes between joints.
To be correct, the length of the exhaust manifold before the gasses from the 4 cylinders come together should be about 32 to 34 inches from the head flange, assuming it is a 4-1 manifold. If it is a 4-2-1 manifold the first 2 pipes should join at between 16 to 17 inches, this is called the primary length, the next 2, the secondary pipes are the same length. The distance to the first silencer or Cat, should be the same distance away from the place the pipes all join.
So why are these distances so critical? The pulses of gas move down the pipe until there is a junction and then reverberate back up to the back of the valve, if these lengths are correct the wave pattern exerts a suction behind the valve head. If these lengths are wrong the pressure wave gets distorted and so looses it’s suction power and in some cases it can actually be worse than the standard manifold, as the waves clash against each other ruling out any suction and even providing positive pressure to hold the gas in the cylinder.
I know many will say, how is this possible, the standard manifold is not anything like the lengths you have quoted. Yes, quite true, here comes a bit of the technical stuff again. The harmonics of the gas and pipe lengths are to do with multiples and divisions of these lengths stated. Lets take 32 inches as the correct length. If you made a manifold that the 4 pipes joined at 64 inches, no problem, if you made one that they joined at 16 or 8 no problem. If the first silencer was 8 or 16 or 32 or 64 inches from where the 4 pipes join together, no problem. Therefore the standard exhaust manifold will have been designed by the manufacturers to coincide with one of these lengths, even though it does look crap.
OK, so where is the problem. The problem is that a lot of exhaust manifold manufacturers do not follow these rules often due to space limitations under the bonnet or for ease of manufacture due to complicated bends and junctions, this being particularly applicable to 4-2-1 units.
So yes on paper a 4-2-1 should give you more bottom end power but if it is not built to the correct lengths it will not and may even be worse than the standard one.

Oli

saxoash · 16th November 2006, 10:16

Great help S34MER, Rep for you :Y: