Mine is the same,have you noticed the improvement in performance,and driveability-mine used to be a slug.
The mpg improvement took some time to realise,I just wasn't putting in as much fuel as before.
de-cat pipe does NOT increase MPG
- Thread starter swampy177
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Mine is the same,have you noticed the improvement in performance,and driveability-mine used to be a slug.
The mpg improvement took some time to realise,I just wasn't putting in as much fuel as before.
waldershelf
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exhausts generate back pressure, keeping the gasses in the cylinders for longer. This is sometimes necessary.
If your engine is not capable of correcting the mixture on-the-fly, then by removing the back pressure (by straightening the exhaust, removing the centre box, removing it entirely etc...) you might end up running too lean. (Too much air, not enough fuel). This will cause your combustion to burn hotter.
If your vehicle is capable of dealing with the increase airflow through the cylinders, then I guess it shouldn't be an issue, and more fuel should be shoved in there with the air to keep the mixture at the correct ratio.
Therefore... if you remove the center box of the exhaust, you will reduce back pressure. you will therefore burn more fuel because the MAF meter will detect more air passing through and will therefore put more fuel in.
If you still have a centre box and a cat, however, but your cat is collapsed and/or blocked, then you will could be running rich (not enough airflow). In reality, though, the MAF meter will detect lower airflow and put in less fuel, causing you to have to rev harder to achieve the same goal.
So... with a collapsed/blocked cat, you are having to push the accelerator harder to achieve the same goal (burning more fuel), and with no cat and no centre box the airflow is increased and you are using more fuel, but not necessarily with any power gain.
With the cat removed, but the center box still in place, you are allowing more air to pass through, but not too much, so making the balance a little "nicer".
I think this makes sense, anyway... from my basic understanding of the four stroke cycle!!
Oh, and i'm no expert on landy's in particular, nor engines - this is just from my understanding, so please correct me if i'm wrong!! I'm keen to learn here too
most of what you say is true for petrol engines but not for diesels. Diesel engines run with sub stoichoimetric consumption at all times the lower the load and accelerator (diesel regulator) position the further below stoichiometric the combustion process becomes. Only at full throttle does a diesel approach stoichiometric combustion, however no matter how well designed a car engine is it cannot achieve stoichiometric combustion and will always require some excess air to achieve complete combustion (this applies to both petrol and diesel) This is why tweaking the fuelling on a turbodiesel can if taken too far produce black smoke, which is unburnt fuel.
Turbo engines (petrol or diesel) are less susceptible to exhaust tuning than none turbos due to the flow resistance in the turbo, generally a turbo engine will perform best with minimum resistance in the exhaust. The resistance to flow caused by the turbo nullifies any potential benefits of exhaust tuning as such resonance management, reverse pulse tuning, expansion chambers (in 2 strokes) etc. Generally speaking proper exhaust tuning only really works with one exhaust per cylinder systems, performance exhausts for multicylinder applications are generally designed to get the gasses away from the engine as quickly and efficiently as possible. (Caveat. not going down the more complex subject of air inlet control found on modernish diesels or length tuned tubular header exhaust systems)
swampy177
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Wow think i have really opened a can of worms here
From what i understand about exhausts (which is probably wrong) there is a 'optimum' point which is designed to keep a little of the back pressure in the pipe to heat the exhaust to allow the gases escape the fastest .
A pipe that has too little resistance in it will flow too quickly and the exhaust will heat up quick , likewise with a pipe that has too many restrictions in it will be too cool and the gases will clog up .
Thats why race cars , bikes etc have exhaust wrap on them to keep the exhaust at the perfect temperature too allow the gases to escape quick enough !
Not sure if that is right but please correct me if it isn't
From what i understand about exhausts (which is probably wrong) there is a 'optimum' point which is designed to keep a little of the back pressure in the pipe to heat the exhaust to allow the gases escape the fastest .
A pipe that has too little resistance in it will flow too quickly and the exhaust will heat up quick , likewise with a pipe that has too many restrictions in it will be too cool and the gases will clog up .
Thats why race cars , bikes etc have exhaust wrap on them to keep the exhaust at the perfect temperature too allow the gases to escape quick enough !
Not sure if that is right but please correct me if it isn't
fishsponge
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Thanks for that!
very interesting indeed!I based my knowledge on how my old motorcycle works, which is, of course, petrol!
So... is it better for fuel economy to have a smaller diesel engine working hard rather than a huge diesel engine practically ticking over?
As for never reaching stoichoimetric combustion, I guess this makes sense, because in order to achieve it you would need to have your diesel particles spread throughout the cylinder perfectly equidistant from each other, with the same number of air particles in between each of them, and the ignition to happen throughout the cylinder at exactly the same time rather than starting somewhere and spreading.
I guess the combustion does start in the entire cylinder at once (pretty much) because it'll all be at the same compression, unlike a petrol where ignition comes from the plug and then spreads. You can't rely on the diesel and air particles all being in the right positions though, I guess!
davek0974
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Interesting stuff this
Also brings to mind an old question of is it more efficient to drive a tdi off the turbo I.e. High gear, low revs or keep it spooling - low gear, high revs??
I was told to change up as soon as possible for economy.
Also brings to mind an old question of is it more efficient to drive a tdi off the turbo I.e. High gear, low revs or keep it spooling - low gear, high revs??
I was told to change up as soon as possible for economy.
oldskool
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Race cars have there manifolds wrapped or ceramic coated to try and keep under bonnet temps down, a restrictive exhaust will run hotter than a free flowing one, primary pipes (manifold) should be seperate and join in a certain order so as to prevent pulsing from one cylinder exhaust goin up another, also the length of the primary pipes can make a large differance to performance and should all be the same length.Wow think i have really opened a can of worms here
From what i understand about exhausts (which is probably wrong) there is a 'optimum' point which is designed to keep a little of the back pressure in the pipe to heat the exhaust to allow the gases escape the fastest .
A pipe that has too little resistance in it will flow too quickly and the exhaust will heat up quick , likewise with a pipe that has too many restrictions in it will be too cool and the gases will clog up .
Thats why race cars , bikes etc have exhaust wrap on them to keep the exhaust at the perfect temperature too allow the gases to escape quick enough !
Not sure if that is right but please correct me if it isn't
M6SJG
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Interesting stuff indeed! - I'm convinced. de-cat is the next job on my `to do list'... well after the replacement of that pesky oil pump bolt...
waldershelf
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Wow think i have really opened a can of worms here
From what i understand about exhausts (which is probably wrong) there is a 'optimum' point which is designed to keep a little of the back pressure in the pipe to heat the exhaust to allow the gases escape the fastest .
A pipe that has too little resistance in it will flow too quickly and the exhaust will heat up quick , likewise with a pipe that has too many restrictions in it will be too cool and the gases will clog up .
Thats why race cars , bikes etc have exhaust wrap on them to keep the exhaust at the perfect temperature too allow the gases to escape quick enough !
Not sure if that is right but please correct me if it isn't
I'm not sure it's you that opened the can of worms, it might be me rambling on about stoichiometric combustion. I'll try and add to the uderstanding a bit if I can. Its not really about exhaust gas temperature, more to do with gas density and velocity, but you are right that temperature affects both, one of Boyles laws would explain it I'm sure.
Back pressure/pulse management in exhausts produces its best results with highly? tuned engines where the end of the exhaust cycle overlaps the next induction cycle a carefully designed exhaust will produce a pulse wave in the exhaust that results in a low pressure point in the cycle that sucks the exhaust gasses from the cylinder and then a higher pressure pulse that stops the new charge escaping through the still open exhaust valve. In theory this works to its optimum on one cylinder at a fixed RPM in practice compromises are made which trade drivability against maximum power
A constant restriction in any exhast system will reduce efficiency, however the requirement for silencing does introduce a restriction and clever engineers minimise the effect with their designs.
waldershelf
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Thanks for that!
I based my knowledge on how my old motorcycle works, which is, of course, petrol!
So... is it better for fuel economy to have a smaller diesel engine working hard rather than a huge diesel engine practically ticking over?
As for never reaching stoichoimetric combustion, I guess this makes sense, because in order to achieve it you would need to have your diesel particles spread throughout the cylinder perfectly equidistant from each other, with the same number of air particles in between each of them, and the ignition to happen throughout the cylinder at exactly the same time rather than starting somewhere and spreading.
I guess the combustion does start in the entire cylinder at once (pretty much) because it'll all be at the same compression, unlike a petrol where ignition comes from the plug and then spreads. You can't rely on the diesel and air particles all being in the right positions though, I guess!
I come from a motorcycling background too, Do you recall the old speed record bikes that had long tubular unsilenced exhausts that produced massive horsepower and narrow power bands. The Guy that really understood exhausts was Walter Kaaden who in the 1950/60s revolutionised motorbike racing with MZ and the phenominal 2 stroke racers I think one of the Jap bike producers persuaded him to defect.
What you say about the combustion process is I'm sure bang on which is why all engines are designed to run with excess air to ensure all the available fuel meets with enough oxygen at some point in the cycle to complete combustion.
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fishsponge
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waldershelf
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Ah well, feeling quite old now, my kids were born in the 80'sNo, I was born in the early 80s...
fishsponge
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I saw a sign in the front of an old truck a while ago... here it is!
I intend to live my life by that sign!!
I intend to live my life by that sign!!
oldskool
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davek0974
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Exactly. After the turbo, and the rest of the exhaust system, then a normal fully-working cat is not a restriction, so it doesn't affect performance (either fuel economy or power). Maybe there's a lot of Discos out there with blocked up cats which can cause a restriction. Mine wasn't, and it didn't give any benefit once removed.
Discodave2011
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Hi guys, fitted de-cat pipe to my 300tdi auto last night, er in doors was NOT inpressed as it was Valantines day!! went on test drive to get er in doors some flowers, dont know why i bothered? But i found it made a big difference to performance, acceleration was better, engine reved more freely, just altogether better, will have to check mpg when i have covered a few miles.
Brian S
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I removed my cat and fitted an erg blanking plate and did not notice much difference in mpg or power.
I have since removed the viscous fan but I have never heard my turbo whistle.
I know the turbo works as there was no smoke or movement in the turbo spline and the landy seems to have enough power to indicate turbo assistance.
Should I hear a whistle or do only some do it?
I have since removed the viscous fan but I have never heard my turbo whistle.
I know the turbo works as there was no smoke or movement in the turbo spline and the landy seems to have enough power to indicate turbo assistance.
Should I hear a whistle or do only some do it?
Whistling turbo means a leak in the piping or air filter system somewhere.
Brian S
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Cheers. That's what I thought. Mines all good then
