024
19.04.2006, 14:38 Uhr
Twix
ADMIN
|
Mein English (deutsch auch) ist zu begrenzt,
aber viele Fragen werden hier geklärt: Zitat:
Exhaust Manifolds
Regarding manifolds 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. A particular car that was built that no one could really improve on the standard manifold was the 205 MI16. It was made of course cast iron but was worked perfectly.
One reason I am mentioning all this is that some people were contacting us saying a manifold was available for the Saxo that was stainless steel and cheaper than our mild steel one. I rang the company up to ask details and, yes they could supply it cheaper but only if I bought 10 at one time, so the price problem disappeared. I then went on to ask technical specification as it was a 4-2-1, when given the dimensions of the lengths of pipes, I had to laugh, there was no way this manifold could work.
... Gruß ... .Twix ...
--
I would like to change the world, but God doesn't give me the Source Code !
Dieser Post wurde am 19.04.2006 um 14:38 Uhr von Twix editiert. |
