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Free flow Exhaust - is it ? - Induction/Turbo/Chargecooler/Manifold/Exhaust - The Lotus Forums Jump to content
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Dave Freeman

Free flow Exhaust - is it ?

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As with all modifications to this car one thing always leads to another. I now have a shinny new free flow manifold, the turbo will soon be refurbished and will match the S4 engine, however the exhaust may be restricting the exhaust gases?

My stainless exhaust was built locally using a power flow silencer, the outlet from the turbo follows the normal route until it reaches the silencer, so one pipe into the silencer and two pipes out one next to inlet and the other I single exit. The two pipes then curve back into twin out lets at each side.

The sound is not as loud as it was, there is some nice popping on overrun, so all seems good.

BUT, how, without changing the whole exhaust do I check if there are any restrictions, in other words is it a free flow exhaust. This question arises because having spent money on the manifold and the turbo I do not want to loose power and torque due to a substandard restrictive silencer.

So I guess the question is now can I check if the silencer is not restricting gas flow.

Also has anyone fitted a vortex silencer, these seem to offer power increase and reduced size, they are supposed to be very good.


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Ask the silencer manufacturer?

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From my experience and data available, you will find that there are more gains to

be made now from the bore of the actual pipe. At present you will find more pressure

resistance in the primary section of tube itself rather than than the silencer...

Every modification has a knock on effect. By improving a known weakest point

you only move it to another area... In this case the new manifold has now allowed a

greater flow to the turbo and post turbo exhaust making these the new weak spots.. by removing

the Cat. the flow is greatly improved and more gains had...However the weak point now

is the flow restriction of the pipe not the silencer box. The gasses will be backing up in the

primary section of the pipe with heat generation. As the gasses move down the system they

cool loosing volume and pressure by the time they reach the silencer box. Any expansion in

surface area here acts mainly as noise suppression regardless of design as long as it does

not contain a constrictor.

Improving an already high flow silencer will only have financial gains to the supplier..

By expanding the post turbo pipe with a taper immediately after the turbo will give a two fold

beneficial effect. 1, The rapid expansion of the gas will create a lower pressure zone on the

exit of the turbo allowing better, quicker and more sustainable spool up. 2, By expanding the

​area you will reduce the temperature which will in turn help reduce the volume increasing the

pressure differential.. win win..

By the time the gasses get to the back box, as long as it is a straight through high flow unit there

should not be any negative effect regardless of size...

The weak point will now have moved to another zone on the induction/exhaust cycle of your engine.

This is all part of the principal system used when developing mine...

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