Outer Limits 4x4 Board

G'day Guys,
First post,nice to meet yas.
I have a GU 4.2 Turbo Diesel.Am looking at getting a 3 inch mandrell exhaust system in Stainless put on it with no muffler.Does the engine need backpressure?Everyone seems to say 3 inch all the way for this donk.
Will it give good torque gains?How noisy will she be?Will it have more turbo whistle?
Cheers!

From my uderstanding, any turbo vehicle (petrol or Diesel) does not need back pressure to assist with "scavenging" as the turbo will force the fuel/air through the cylinder!

Gabe

The quicker you can get the exhaust gass away from the turbo, the quicker it can spool up and respond to different engine load.
Layto....

short answer. No. Backpressure kills a turbo.
The turbo will spool up much, much more quickly, and it will increase power/torque right through the range with a 3" system.

I've just built a 3" system for the little 2.5litre in the Landy, and the results are exellent. Much, much better at the bottom end, and it has dramatically increased the rev range, meaning I can hold gears for much longer when climbing. It also sifgnificantly dropped EGT's.

Remember that the exhaust is only half the equation, and that tweaking the injector pump fueling and boost on a TD42T will really gain some dividends
Of course it will be noisier without a muffler, although the turbo acts as a pretty good muffler in its own right. I'm pretty sure I'll be installing a resonator on mine (a 4cyl) as it is getting a mild drumming at 100km/h, which will drive me nuts on a trip.
Our Patrol gets the treatment next...

Just make sure the dump pipe for the turbo has the inlet matched to the outlet of the turbo. A lot of turbo have a squarish outlet and the dumps are round hindering the turbo.

turbo itself will create enough back pressure on the engine to prevent valve damage

if you wanna get the facts, ask in the Exhaustfix thread

Buckshot wrote:G'day Guys,
First post,nice to meet yas.
I have a GU 4.2 Turbo Diesel.Am looking at getting a 3 inch mandrell exhaust system in Stainless put on it with no muffler.Does the engine need backpressure?Everyone seems to say 3 inch all the way for this donk.
Will it give good torque gains?How noisy will she be?Will it have more turbo whistle?
Cheers!

Yes, your engine needs backpressure for the valve timing to work as expected. This is primarily provided by the exhaust turbine, and less by the exhaust system downstream from the turbo. The turbo itself works best with minimal backpressure, so a 3" mandrel bent exhaust will help.

Don't know about noise or whistle.

Cheers,

Scott

Buckshot wrote:G'day Guys,
First post,nice to meet yas.
I have a GU 4.2 Turbo Diesel.Am looking at getting a 3 inch mandrell exhaust system in Stainless put on it with no muffler.Does the engine need backpressure?Everyone seems to say 3 inch all the way for this donk.
Will it give good torque gains?How noisy will she be?Will it have more turbo whistle?
Cheers!

NO NO NO NO NO NO it dosent backpressure

can you hear that

As others have said, no backpressure is best. However in future all diesels will be fitted with filters/catalytic converters in the exhaust. These have quite a bit of back pressure, which for most systems increases until the filter is cleaned/regenerated. I have seen some of the dyno tests results during the development of these systems, and there is, as you would expect, a decrease in engine performance as back pressure increases.

Cheers fellas,3 inch Mandrell on the way!

correct me if im wrong but backpressure is a word used for lack of knowledge of another word. my understanding is that every exhaust has to be a certain size to allow the exhaust to flow to the valves flow rate. if your exhaust is too big then there isnt enough exhaust pressure created and the flow is too slow. if it is too small the same happens.

evan

Buckshot wrote:G'day Guys,
First post,nice to meet yas.
I have a GU 4.2 Turbo Diesel.Am looking at getting a 3 inch mandrell exhaust system in Stainless put on it with no muffler.Does the engine need backpressure?Everyone seems to say 3 inch all the way for this donk.
Will it give good torque gains?How noisy will she be?Will it have more turbo whistle?
Cheers!

The turbo will always have backpressure...simple. Backpressure will occur just after the wastegate and cause turbulance to the air. Technically speaking if you want the best results with an internal gated turbo then you need to seperate the wastegate gas from the exhaust impellar for as long as possible. In addition to this, there should me a large jump up in pipe diameter just after the exhaust housing. This is to aid in the "expansion" of the exhaust flow. A bigger exhaust will alleviate some or most of this and cause the motor to run better. However, that is only 1/3 of the equation. You also have fuel and inlet. Get a higher flowing filter to go with the exhaust (better element like K&N) and you are mostly there. Now take it to the dyno and get it tuned because all of the mods that you have just done make the motor "flow" better. This means that there should be more air not only available, but being used. This means that the fueling is now not optimal for your setup. Also boost should have risen as well....

chunderlicious wrote:correct me if im wrong but backpressure is a word used for lack of knowledge of another word. my understanding is that every exhaust has to be a certain size to allow the exhaust to flow to the valves flow rate. if your exhaust is too big then there isnt enough exhaust pressure created and the flow is too slow. if it is too small the same happens.

evan

No. This is a turbo motor...all of the "flow" that you are talking about happens before it even hits the true exhaust of the motor. Your headers or turbo manifold will be matched to the turbo from factory so there should be no problems there. We are talking about a 4.2L diesel motor, which has enough exhaust flow to blow your pants off. The problem with turbo restriction occurs not so much at the valve, but at the back of the turbo(exhaust housing) because of the wastegate and exhaust impellar causing interference with each other. On some performance model turbos, where the interal waste gate sits they have alleviated the housing slightly to reduce "back pressure" at this critical point.

I have just fitted a factory turbo to my GU TD42 DX wagon and was driving it for 2days with 400mm of 2.5inch pipe straight out of the dump pipe, before fitting a sports 2.5inch system. The difference the system made was more power/torque and less noise. I was told some backpressure was needed for the motor to work better and I have had first hand experance with the difference it makes. The noise no pipe make sounds like it is going faster but it wasn't.