9 replies to this topic

[AGRO_RB]

Hoping someone can shed some light on this, I'm looking to replace my standard exhaust system, manifold, pipe, silencer, everything. I'm looking at the Minisport Stage One half kit which includes an.LCB manifold, and either a Sportex DTM style twin center exit, or the much more expensive Playmini 3" equivalent. We don't salt our roads at all over here so the horror stories of Sportex exhausts rusting out don't really phase me much, I like the sound of both.systems after watching a few YouTube videos but with the Sportex being more than.half the price I'm more inclined to go for that... It's a standard 998, not a 1380 race donk. In saying that I don't mind paying for quality...

Are there any detrimental effects to using an LCB on a smallbore motor and is the Playmini system overkill? It doesn't specify on either the Playmini site or Minisport whether it's suitable for smaller engines.

The Stage one kit IS suitable for the 998 but surely the LCB would only really be effective at high rpm? Or am I just overthinking this too much?

[Vipernoir]

Maniflow magic pipe and an RC40 every time for me.

[AGRO_RB]

I want to.get rid of the standard manifold though, I'm seeking a bit of performance, not just looks, and none of the Maniflow systems really appeal either.

[Vipernoir]

Nowt wrong with the standard exhaust manifold if you chop off the inlet.

[Blitzman]

I think Maniflow are one of the best.

How about this.

http://www.minispare...px|Back to shop

The Maniflow Cooper Freeflow manifold is fine.

The problem with too big a manifold/exhaust is losing low down torque or nice pick up in traffic.

[Cooperman]

The ideal size for the exhaust pipe on a 998 in I is 1.625" diameter. Any larger and the exhaust gas velocity is too slow and the gas inertia needed to make the exhaust system most effective is lost.

With the large Sportex or PlayMini systems expect to lose a few bhp rather than gain anything. In fact they are very poor and cannot be described as 'performance' systems, unless it's 'losing performance systems'  .

Even the Maniflow 1.75" system is slightly too large for a 998 unless it is revving to over 7000 rpm.

The ideal system is an original 998 Cooper ex. manifold and exhaust.

[AGRO_RB]

Looked at that, it's out of stock and not the DTM center exit I want...

[Cooperman]

To explain (again!), the design of a performance or optimum exhaust system depends on two factors; the volume of exhaust gas passing down the pipe at the revs for maximum power and the required speed of that gas.

The exhaust gas is comprised of molecules which have a mass (weight). Once moving there is an ideal speed for the molecules to have the best inertia to exit as efficiently as possible.

A physics expression known as 'Bernoulli's theorem' states that if the cross sectional area of a pipe increases, the velocity of a fluid passing along it is reduced and the local pressure is increased.

So if a single pipe goes into a back box and the exit is two large pipes, then the gas is slowed and the back pressure increases. This causes a loss of exhaust efficiency and thus a loss of power combined with an increase in fuel consumption.

For a twin pipe system to work the twin pipes at the end need to be about 1.125" in diameter for a 998 or 1.25" for a 1275 to give the correct cross sectional area.

But if performance is not important and appearance is desired, assuming one thinks the twin pipes look better, then that is owners choice. Only the engineering design for optimum power is being considered in my explanation as that is what most people seem to want.

[AGRO_RB]

Stupid physics... I never had this problem with big engines!

In that case then, keeping the piping as close to the optimal diameter as possible, could I simply make up a center exit system without any detrimental performance effects?

Even better, can you buy factory style Cooper exhausts brand new?

[Cooperman]

You can buy a 'works rally' type centre exit single upturned pipe from Maniflow. It will probably be 1.75", but as that seems to be all that's available these days and it will work best with a high-revving 998.

It will look like the works rally cars of the 60's and it is what most historic rally cars use these days. here is a photo of mine as fitted to my 1310 cc historic rally Cooper 'S'.

I hope this helps you: