Straight through exhaust

[Patty]

Looking at doing a straight through on my 300tdi was wondering if to remove just the rear and centre boxes or geting rid of the whole lot including the catalytic converter aswel and wondering how wasy it is to do myself?

[wheels244]

Got a straight through on mine.

I bought a stainless decat pipe, stainless centre pipe that replaces the centre box and then took the exhaust out of the side, so no silencers at all.

I fitted a K & N at the same time - the combination made a big difference, the turbo spins ups faster and makes it much more driveable - not as many gear changes.

It does sound a bit more agricultural but definately not too loud.

[Disco Matt]

How easy it is to do will depend on how rusty the old bolts are - as you'd be replacing the whole thing this shouldn't be as much of a problem!

Does anyone make a straight through exhaust kit? Just thinking that the complex bends that take the exhaust up and over the back axle would be quite tricky to get right if you bought various pipe bends. It might be better if you can keep that part of the original exhaust and weld in a new tailpipe.

You could also fit a side exit at the same time - I would like to do this but it would mean hacking a stainless exhaust, which I don't want to do!

[Range Rover Blues]

fit a de-cat front pipe and a sport utility system, it will have the rear boc but it makes very little difference to performance, if anything i think a straight through system will make things worse, all that noise comes from your engine after all.

[J.D.]

Also bear in mind that with all the boxes removed, you will have pretty much no back pressure, which doesn't do the engine any good at all.

[wheels244]

Doesn't the the big blockage that is the turbo provide any back pressure that is required ?

Also, my understanding is the diesel engines prefer to breath as freely as possible.

There is a noticable performance difference with mine 

Not a Landrover engine but the principle is the same

"With a decat, a major exhaust restriction point is removed. Diesel engines in the United Kingdom do not require a catalytic converter to pass the MOT test, which consists of a simple smoke density test. The function of a catalytic converter on the 2.0 HDi is to operate in unision with the Exhaust Gas Recycling system, which was in it’s second generation on this engine. This helps to reduce emissions of NOx and CO. However, in this system the EGR still introduces noticeable throttle response lag, reduces the response of the turbo, and significantly blocks the intake manifold with oil and particulate debris. Removing either the catalytic converter or the EGR, means the other is much less effective and not required, so removal of both is always suggested to maximise the benefits made by removing one or the other. A simple decat and EGR removal can yield almost 5bhp and 5-10lbft more on a standard engine, along with the improved response

As well as reducing back pressure, the exhaust sound quality of the HDi can be greatly improved by adding a free flow exhaust. Turbo response time is improved, meaning more torque and better throttle response, with benefits easily matching those of a simple decat. In combination, a remap of the ECU, a decat, EGR removal, and a free flow exhaust can yield around 125bhp and 205lbft "

Taken from    http://jacmech.co.uk/tuning.html

[boss]

yeah, the turbo is being spun before it reaches the exhaust.making a blockage in the zorst before mufflers get involved. i would atleast put a little box in there, mines a 2.5" bore straight through with a little muffler and its LOUD! not good loud, just loud! it will run best if you sort out all of the induction system at the somew time, pump, filter and zorst. then itll go VRRRRRRROOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM! :D

[wheels244]

A bit more 'evidence'  :)

"Turbo exhaust flow

You want the least backpressure in the exhaust after the turbo for maximum performance, no exceptions.  The problem is that you have to balance maximum performance with emissions and difficulty/cost of fabrication, etc..  Note that this does not apply to with non turbo or supercharged cars, where some exhaust backpressure is normal as a result of keeping exhaust velocity and the scavenging effect from individual cylinders high.  Non turbo cars that keep their catalytic converters are not as significantly penalized by backpressure as turbo cars are.  In most cases, non turbo exhausts want to restrict the piping diameter to some extent to keep exhaust gas velocity high and receive backpressure as a byproduct.  With turbo exhausts, there is no scavenging effect downstream of the turbo, so you want the least amount of backpressure after the turbo for the maximum performance and efficiency.  A turbo exhaust should have the highest energy differential across the turbo (the exhaust gasses are also hot and have a lot of energy) to get the turbo spooled up, and the least backpressure and high velocity exhaust gases after the turbo.  This is because a turbo gets its energy by a pressure ratio.  Image a waterwheel: you want the pressure highest before the waterwheel and lowest after the waterwheel to give it the most energy.

How much power is released by putting a straight pipe exhaust on a TDI?  First, remember that total power is the area under a power curve, not just peak power.  You may not gain much peak power with only an exhaust change but the total amount of power will increase.  Also remember that an exhaust is a basic supporting mod for any future modifications such as a chip, larger turbos, fuel nozzles, etc.  A TDI diesel is throttled by fuel and uses a relatively small turbo with computer controlled fueling.  Peak power may not go up much but combined with chip tuning, it should increase response and area under the power curve, and let any further mods reach their full potential.

Below are some more details on individual components of exhaust systems.  Because you want the least backpressure in a turbo car's exhaust, the ideal exhaust system would produce the least backpressure immediately after the turbo.  Due to routing, emissions equipment, pipe diameter, exhaust gas temperatures/pressures, the perfect diameter changes from car to car, setup to setup.  It's very difficult to know this without extensive testing, so as a rough rule of thumb, a consistent or increasing diameter exhaust as you head downstream towards the tailpipe is best in most cases.  Mandrel bent exhausts are also always better.  A mandrel bend is when piping is bent with a mandrel, or insert, to keep the inner diameter consistent at the bend.  Crush bends reduce the diameter at the bend and reduce smooth exhaust flow.  Most factory exhausts are non-mandrel bent crush style bends, so switching to a mandrel bent exhaust will increase power and efficiency of the turbos and engine with no other modifications.  You also want to avoid very restrictive mufflers, sharp changes in piping diameter, and sharp bends.  As a rough rule of thumb, each 90o bend in the piping has about the same resistance to airflow as 25 feet of straight piping! "

Taken from http://www.myturbodiesel.com/1000q/turbocharging.htm

[Patty]

Well after all the advice which is gracefully recived last nite I removed the centre box and rear box and added a muffler tip.seems to have improved the performance but was wondering if removing the cat converter would have even more effect?

[mikiep1986]

 yes would make a hell of a difference i remeber taking the cat outa my ford focus it was petrol but was soooooo much of a difference loads more power . . .

[Range Rover Blues]

It's not a catalytic converter it's a smoke particulate filter, get rid of it.