Sports Exhaust!?!

[steves944]

OK I finally had enough tonight!
My recently purchased and absolutely fantastic 944 LUX has one thing which has steadily been driving me nuts. Its got a brand new stainless steel exhaust system put on by the previous owner but its too damn noisy!
Sounds great going under bridges or through narrow roads - well it has done for about 8 weeks - but now I've had enough.
The door trim rattles, the body resonates all at a certain frequency and the thrill of the raspy note has gone.
I am going to put a standard system back on so I can enjoy my motoring, and my radio!
I don't know if the straight through exhausy would have added anything to the performance but I feel the car would be quicker with a bit more back pressure.
Would I be right in thinking that?
Thanks

Steve

 

[Eldavo]

No idea but if you want to swap then let me know!

 

[ChasR]

Which engine do you have in your Lux? Is it a 2.5 or a 2.7? AFAIK, the 2.7 had a similar exhaust to the S2, where the factory system had a larger front silencer than the 2.5, with the rear section consisting of a small intermediate silencer and a back box. I know some people have complained about their 2.7 having the smaller 2.5 box on making things loud inside the car.

 

[944 man]

Ive always been massively sceptical about the 'need for back-pressure'. An engine needs an impediment like this like your petrol needs sugar in. These cars already have terribly restrictive manifolds, after all...

 

[ChasR]

So basically Simon, you are saying that the type of exhaust one goes for should not affect power at all (even with possibly a cat in the system) due to flaws elsewhere in the car (I assume here you are referring to the ehxuast and Inlet manifold).

 

[craig2105]

This made me grin as I had exactly the same problem with my S2. But finally, the loud bespoke system is off and awaiting a new (deaf) owner, and I am basking in the civility of a stock front section, Janspeed mid box and Dansk back end. Lovely. Except that on the 5% of occasions when you can open it up a bit, the car now sounds slower unless I crack the window open!

 

[ChasR]

I quite like the sound of the stock system on my S2. But I understand that if/when the front box goes I'll need to make some changes unless I want to pay £400 for a front box from Porsche.

 

[Peter Empson]

I feel you can definately go to far with the exhaust, many years ago we removed the silencers one at a time and there was a definite loss of perceived torque when running what was effectively a straight through exhaust. The noise was quite unpleasent too [] The standard exhaust is definately too restrictive though, so finding a happy middle ground is a good idea.

 

[AfterShock]

Ok true confession time!

In my youth .. my first car was a Hillman Imp. I played around as you do as a "boy racer" and fitted a peco exhaust along with other bits n bobs.

Sounded like a Porsche as it burbled away. Well at that age and in my head it did anyway.

However it wrecked the backpressure and I guess other running systems being a free flow exhust so the car constantly stalled!!

Hugely embarresing to say the least when your the "cool" guy at the lights revving your engine and waiting for the lights to change only to splutter to a standstill and take ages to start again.

Ahhhhh the joys of youth!!!

 

[supersport]

Sounds like mine is the same, I thought it was quite nice but in reality I think it is naff. There is a little rasp when you first put your foot down, but to me it sounds a bit chavvy.

Sadly it is not high on my list of priorities as this is supposed to be a cheap car to run.

 

[944 man]

Engines dont need 'backpressure'! They need a correctly tuned length!

 

[Eldavo]

I thought only 2 strokes needed backpressure?

 

[Diver944]

Hi Steve. Have a look under the car by the drivers seat. Does this system have a small silencer there or just a 'straight through' section? Reintroducing a small silencer there will reduce the noise somewhat.

 

[944 man]

Id say that the resonator makes a very worthwhile difference.

 

[barks944]

I don't think 4 strokes need back pressure either and I agree that they need a correctly tune length. This is about standing waves in the exhaust system as the valves open and close. Its a bit like waves on a beach and you want the waves to be going out not in when you open the exhaust valve as it keep the pressure on the valves low.

 

[JamesO]

ORIGINAL: 944 man

Engines dont need 'backpressure'! They need a correctly tuned length!

Yeah, I was under the impression it was all about scavenging (on non turbo cars) and a good exhaust design, not a large/open exhaust would help empty the cylinders faster.
I may be completely wrong.

 

[Hilux]

Engines dont need 'backpressure'! They need a correctly tuned length!

Not quite true, back pressure plays an important part but is an effect of the tuning of the headers ie: diameter and length in relation to valve size, piston chamber displacement and gas velocity and volume once expanded for it is alternate gas speed (acceleration and deceleration) called pulsing or pulsation that makes an exhaust header work effectively. The rest of the exhaust has cooler gasses expended efficiently with sound deadening as required but still related to the headers performance.

The gases pulse like a wave on an oscilloscope but need to be in syncro with the engine as it expels the gasses and inhales a charged mix.

The pulse (expansion cycle) momentarily drops in speed and briefly increases the back pressure as it leaves the constricted chamber into the header by the action of the exhaust pipe slowing and speeding up the gas as it exits and expands into an open tube thereby allowing the charged air to fill the cylinder as the valves close without letting the charged air through. The gas exits out of the chamber at supersonic speeds but as it expands it slows imperceptively and then speeds up again in a wave formation. The number of waves contained in a given length of pipe all moving at the same (most efficient speed) is what tuning headers is all about.

A straight through exhaust that 1) allows the gasses to pass too quick 2) doesnt restrict expansion 3) increases or restricts exit gas speeds too much and therefore doesnt allow proper pulsation will lower the engines capabilities henced tuned headers are required as 944 man says.

 

[wolfie308]

Due to a slight blow in my rear box, I have been considering replacing the orignal standard item with this one from S.A.R.......

However, Simon at S.A.R told me that Janspeed had changed the design to this.....

He asssured me the link pipe would not be visible when fitted, but I'm not so sure myself. I think if you're going to have something this 'shouty', the detail has to be correct. What does the panel reckon? Has anyone here fitted one to an S.2?

 

[Diver944]

ORIGINAL: wolfie308

What does the panel reckon?

Hmmmmmmm, don't like that tiny link pipe at all

 

[simch1]

Try Pipewerx for one. Ian Birch is well known and respected for his fabrication abilities and can build you what you want, noise and design wise. IIRC its about £350 from DP back.