equal length header?

[mr_smash]

im thinking of going 4 a equal length header.anybody fitted 1?if so whats the best make as ive seen several companies selling them.Also are the gains noticable enough 2 justify the expence??

[chrisp]

You do realise you will loose the off beat flat four burble. The unequal length headers causes the noise, thats why the WRC cars dont sound like our scoobs (amongst other changes). Should give you a bit more power by better airflow and breathing.

[Money]

Best headers are the Gruppe S ones. All the top guys are using them and swear by them

[McScooby]

NNOOOOOOO!!!!!! Don't do it, like Chris says, you'll lose the rumble of the boxer although you will get more power a la WRC......

[mr_smash]

ahahah ..but is a cool sound more importany than more power?......let the debate begin..heheh;}

[phil]

Going to show my lack of technical knowledge here

But why do you lose the burble?

[mr_smash]

yeah good point why do u loose the burble?we want detailed science and physics explanationes..hehe

[Fatmanscooby]

I dont know but they do sound pants

[Money]

<< I dont know but they do sound pants >>

lol!

Dont know if you lose the burble - but if you have a big exhaust out the back, like a momma blitz, who cares. You cant here anything anyway! lol

Why change a stereo system - simple to make it better.

Why change headers - more power/torque

Easy

[Fatmanscooby]

No really they sound like milk floats, i would rather have that burble whats a couple of horses between friends.And they are expensive, i rest my case

[stormy]

Was up at Powerstation on saturday, soon as I can afford it will be going for the headers.

Yes you loose the burble but as mentioned before you get the power plus PS are of the

opinion that it saves you melting piston number 3, he showed me some burnt up samples

Worth giving Dirk a call, he reckons 25ibs more torgue through the gears and thats great.

I will go for the downpipe with sports cat first and then the headers as I want the car to be

MOT ready. Worth a call had a look at the kit and the finish is fantastic.

Far as Im concerned Burble can go as long as I get more torque i.e drivability and save the

STI piston number three. Cost is £450 approx for the header plus £750 for the down pipe

with sports cat, clearly the down pipe with out cat will be about £300.

Im convinced.

[SCOOBY1998S]

The note and the capability of an exhaust is down to six main factors.

1. The way the cams open the exhaust valve, speed and size of valve

2. The interaction between the sound wave pulses in the exhaust

3. The effect of the turbo on the said sound waves

4. The effect of the silencer in diminishing the sound pulse.

5. Temperature and consistency of the exhaust gases

6. The bore of the exhaust.

When an exhaust valve opens a pulse of sound energy is released, along with the plug of exhaust gas. This sound energy travels down the exhaust until it gets to either a collector box, this needs a volume of at least 4 times the swept cylinder, or out of the exhaust at the back of the car.(Collector boxes have not been used for many years), when the sound energy pulse gets to the rear of the car an inverse wave travels back up the exhaust and can be used to scavenge gas from the cylinder that has currently got its exhaust valve open. The timing of these pulse is an art, as they are heavily dependant upon the speed of the pulse in the hot exhaust gas and the manifold that is being used.

In a 4-2-1 system it is highly likely that the inverse pulse will be split evenly as it travels back up the manifold, first in to 2 and then in to 4, meaning that each exhaust valve gets an equal share of the scavenge across the rev range.

In a 4-1 system this is less likely, as the pulse will probably favour a certain set of cylinders, and as such the benefits are not seen until the revs get higher, resulting in a peakier engine. this is exactly what subaru want for a rally car where the driver keeps the car in a very narrow rev band, but not necessarily what you want on the road, as a broad power band is better. You can see this as the major manufacturers such as HKS and Janspeed only really sell 4-2-1 systems to the general public.

With the addition of the Turbo in the exhaust stream there are some extremely complicated interactions in the sound pulses, however, the above still applies, but it is more difficult to perform any sort of accurate calculation.

The bore and route of the exhaust has little impact upon these soundwaves, so long as the bore can handle the amount of gas to be expelled and there is at least a free flow, i.e no 90+ degree bends, curved bends are ok up to high angles. A very large bore exhaust does not help and it can cause some problems.

A guy called John Morrison wrote a book on the scientific design of exhaust and intake systems (Intakes can be pulsee tuned as well.)

His Book

That's about as much as I can remeber, but if there are any questions please post a reply

[phil]

Well that answers it for me

Thanks

[Fatmanscooby]

Yeh thanks

[chrisp]

Yep didnt know the techinical bit only that the exhaust gases travel different lengths (unequal lenghts) which is which why you get two different pulses of sound. Giving the off beat sound.