Thread: EXHAUST MODIFICATIONS

I don't think much will be achieved on the performance front as most of the exhaust will be too small. Increasing the diameter will increase performance and possible boost pressure without doing anything else. My understanding performance comes from efficency, ie get fuel plus air in and exhaust out in the least conflicting way, so that as little as possible is lost through restrictions.

Manufacturers need to choke up engines these days to comply with emissions and noise and employ a range of "restrictions" on an engine to meet those requirements. Drinking straw exhaust on a medium engine is one way, another is block up the intake and lastly tune the computer to suit those restrictions to reduce emissions. [img]style_emoticons/<#EMO_DIR#>/sad.gif[/img]

Increasing exhaust diameter has it's merits and limitations by way of the exhaust "note" becomes more noticable and tends to whistle due to the turbo. The hot car scene generally talk about 2 3/4~3inch from the turbo back with the benifit of increased flow rate. You can also generally get away with only one muffler due to the silencing effect the turbo turbine. The more flow the engine has, the more potential it develops and more flexible it becomes.

Generally changing the exhaust results in a few more horsepower and couple of extra pounds of boost for free. Though changing the exhaust alone isn't considered a huge "bang for buck" modification but should be thought as part of the overall tuning of an engine to deliver characteristics desired. [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img]

I'm told you can get a bit less restriction without excessive noise in a 300tdi be replacing the large front muffler with a straight pipe section. The Pommy magazines advertise these, expecially for Td5s, but here you have to get an exhaust workshop to custom make it for you.

You can have the pipe section welded-in or, as I'm planning to do, get a second flange fitted where the muffler outplet pipe is cut, so the original muffler can be re-fitted if I don't like the result or come to sell the car.

No offence Jay, but a less restrictive exhaust shouldn't change the maximum boost pressure at all, as it's controlled by a watesgate on Tdis. What it should do is let the turbo spin-up a little faster and at slightly lower engine rpm. And with Tdi engines, any improvement in building boost is a good thing.

NH, in the Pommy LRE forum 'Tech Acrchive' is a huge thread on 'tuning' the Tdi injection pump. I'm sure the DTS and other turbo swaps give good results but if you're prepared to study-up on the subject, you may find you can get very satisfactory results from doing your own 'tuning' mods - and at a tiny fraction of the cost. There's also a thead about this just down the page a bit... Where are you, by the way?

No offence as you're right, most turbo engines have waste gates to limit boost but just because it's there will mean everything remains equal if you start changing things. This could get technical and somewhere I don't really want to take this as we're no longer in 4by land but hot car scene. So I'll stick to examples.

Diesel vs petrol, EFI vs mechanical injection aside, wastegates work on two things, back pressure and manifold pressure. It's been written about in every hot car magazine published back to around the time Ford stole Mazda's Familia GTX/GTR and rebadged it the TX3. Scoobs reinvented the turbo hatch with WRX in the 90's. If ever examples wre needed to show any part of tweaking a turbo vehicle... these would be them. There's all sorts of agruements about dyno readouts but 17yrs of tinkering must show up something with changing exhaust sizes ? :?

BD4's, in Gladeville, project used to be a 200SX, for those that don't know it's a turbo 4cyl. They bought it as standard and dynoed it before the modifying to get a base reading to monitor the change in performance. They then bolted on a full 3in replacement HKS system with only one muffler then dynoed it again on the same machine without retuning the computer. Boost went from 8psi to 12psi and the power curve had an extra 13kw mid range. 13kw by doing nothing but increasing the exhaust and reducing back pressure from the turbo :!:

As for swapping turbos, I'd be prepared to wind the wick up on the standard one first after changing the exhaust as it'll be found for more boost the EGT will remain the same. The bigger the turbo the faster you have to turn the motor to get boost, which limits off road appeal.

And that's where I'll leave it. [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img]

Hi JH
On my mitsi Trytoo,which is the same size as a TDI(2.5 TDI Mitsacrappy STYLE!!!!).I have a 2.5" "dump pipe" from the turbo for the 1st 2 feet,after that its 2 1/4" with a "straight thru" muffler,ie you can look straight thru it.
Noise levels are not greatly increased as the turbo is in effect a "muffler",however you do get a half decent growl under full throttle.The best improvement was the decrease in turbo "lag" the turbo spools up quicker with less backpressure.
I would think you should get a similar result with your Disco.
Andrew

Originally posted by JH
IS IT POSSIBLE TO GET MORE POWER OUT OF THE 300 TDI DISCO BY CHANGING EXHAUST COMPONENTS AND WHAT WOULD THE POWER GAIN BE. ALSO ARE THERE ANY BAD SIDE EFFECTS.

Have heard the 200 TDi is less restrictive, in the UK this has become the choice for slight extra power.

LRH.

Originally posted by Hellspawn
...most turbo engines have waste gates to limit boost but just because it's there will mean everything remains equal if you start changing things. This could get technical and somewhere I don't really want to take this as we're no longer in 4by land but hot car scene...

...And that's where I'll leave it. [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img]

Hi Jay,
You raise some interesting points. I'll have a think about your examples and get back to you. But my laptop has to go into dry dock for a couple of days, so it might be later in the week.

As suggested, make sure you have a good dump pipe of the exhaust housing and pop on a straight through muffler and you will certainly notice the difference.

Jay,

I can't say I completely agree with you here. The wastegate is the means by which pressure is regulated in a turbo. It may be activated mechanically, like a thermostat, or by the ecu, ah la XR6T. The wastegate will vent into the exhaust or the atmosphere (not really legal) to get rid of excess boost. Changing the exhaust alone cannot change the pressure at which the wastegate operates, provided it is still allowed to function as normal.

A larger turbo does not necessarily mean that you need more revs to spool it up. If it is designed with appropriate aspect ratios then it can spool up even quicker than a smaller one, within reason. a good compromise is to mate a larger inlet housing/impeller to the std exhaust housing. This will allow it to spool up pretty much as normal and will actually be providing more boost at a given rpm because the inlet is flowing more air. This just means that max boost should be achieved earlier. Cleaning up the efficiency of the std piping is one way of making significant improvements in a boosted engine, relatively cheap and easy too.

Waste gate on TDIs is operated by turbo boost on a diaphram. Depending on which way it opens exhaust back pressure could have an effect on when it opens so boost may change with an exhaust but not sure which way up or down. Having said that they all seem to have the gate adjusted or not adjusted to different pressures. With a super charger a good exhaust actually drops the boost because it is easier to fill the cylinder. Boost pressure is really a bit of a misnomer because it relates to manifold pressure and doesn't mean you are filling the cylinder with charge. Eg the more air the engine can move the less the boost will be for the the same blower rpm, I guess on a turbo the extra exhaust will spin it up so maybe it works out the same, with a super charger however you have to gear it up. I'm a supercharger man myself never got hooked by the turbo craze in the 80's