Thanks for that makes sense because the multijet is obviously the newer engine. Is the JTD just a standard diesel then? Well apart from it being turbo of course.
General Disappointing Multijet
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General Disappointing Multijet
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Im guessing the JTD will have commonrail technology.......What that is I havnt a clue.
(I was trying to sound clever
)
(I was trying to sound clever
)JTD Monkey
Member
Sammy's description of common-rail is indeed correct.
A brief history of the modern diesel:
Most diesels up until 15 years ago were 'indirect injection'. This meant the fuel was pre-heated in an advance pressure chamber (diesel ignites because of high pressure not ignition like a petrol, hence no spark plugs). This made them reasonably quiet but also not as economical as they should be as some fuel was lost in the 'pre-heat' process.
About 15 years ago 'direct injection' diesel became more popular (the most obvious being the 1.9TD in the Tipo/ Tempra and the 2.0D/ 2.0TD in the Montego/ Maestro). Direct injection means this 'pre heat' does not happen as fuel is pumped into the cylinders direct, so there is less waste but the process of 'exploding' diesel from cold requires greater pressure and is more noisy because of this (think of hitting a sledge hammer onto a cherry to pop it in comparison to hitting a sledgehammer onto a walnut. The impact with the walnut will make more noise). The engine is also cleaner (less fuel wasted) and more powerful (there is more fuel in the cylinder to 'explode')
All manufacturers knew direct ignition was the way forward for cleaner, more economical diesels but the refinement problem was difficult to resolve, hence for much of the 1990's the 'indirect injection' remained popular (the ubiquitous 1.9D/ TD in the Peugeot Citroen Range, Vauxhall and Ford Diesels along with much of Fiats range. Not to mention BMW and Mercedes diesels)
The breakthrough in this technology came when Fiat, Bosch and Mercedes worked together to develop the 'common rail'. Put simply, this unit is a single rail of microscopic diameter. Fuel is injected through it at such a high pressure (1600 bar generally) that when it arrives into the cylinder it is at such high-pressure it heats-up immediately. Hence no fuel is wasted (it is all in the cylinder) but there is no need to pre-heat before the 'explosion'.
VW groups 'Pump duse' diesels used a twin pump system (hence the name). This was much lower pressure than a common rail (about 800 bar) but could get the same amount of performance (2 pumps each putting fuel into the cylinders). However, because the pressure is lower the fuel was not as warm as in a 'common rail' system, it is still noisy. However, performance is as good as common rail because 2 pumps at 800 bar mean as much fuel as 1 pump at 1600 bar. VW are now moving away from 'pump duse' as the ability of the system to undertake further developments is limited. Most VW group diesels above 4 cylinders are now common-rail.
Multijet is simply producing multiple (hence the name) squirts of smaller amounts of fuel per cycle of the piston (and crank). Bigger squirts of fuel create more of an explosion, hence more noise. Smaller (but more) squirts produce a smaller and quieter explosion.
The first common-rail diesel to the market was.... the Punto 1.9JTD.
Anyone bored yet?
p.s. Whether a car is turbo or not does not affect the method of combustion
A brief history of the modern diesel:
Most diesels up until 15 years ago were 'indirect injection'. This meant the fuel was pre-heated in an advance pressure chamber (diesel ignites because of high pressure not ignition like a petrol, hence no spark plugs). This made them reasonably quiet but also not as economical as they should be as some fuel was lost in the 'pre-heat' process.
About 15 years ago 'direct injection' diesel became more popular (the most obvious being the 1.9TD in the Tipo/ Tempra and the 2.0D/ 2.0TD in the Montego/ Maestro). Direct injection means this 'pre heat' does not happen as fuel is pumped into the cylinders direct, so there is less waste but the process of 'exploding' diesel from cold requires greater pressure and is more noisy because of this (think of hitting a sledge hammer onto a cherry to pop it in comparison to hitting a sledgehammer onto a walnut. The impact with the walnut will make more noise). The engine is also cleaner (less fuel wasted) and more powerful (there is more fuel in the cylinder to 'explode')
All manufacturers knew direct ignition was the way forward for cleaner, more economical diesels but the refinement problem was difficult to resolve, hence for much of the 1990's the 'indirect injection' remained popular (the ubiquitous 1.9D/ TD in the Peugeot Citroen Range, Vauxhall and Ford Diesels along with much of Fiats range. Not to mention BMW and Mercedes diesels)
The breakthrough in this technology came when Fiat, Bosch and Mercedes worked together to develop the 'common rail'. Put simply, this unit is a single rail of microscopic diameter. Fuel is injected through it at such a high pressure (1600 bar generally) that when it arrives into the cylinder it is at such high-pressure it heats-up immediately. Hence no fuel is wasted (it is all in the cylinder) but there is no need to pre-heat before the 'explosion'.
VW groups 'Pump duse' diesels used a twin pump system (hence the name). This was much lower pressure than a common rail (about 800 bar) but could get the same amount of performance (2 pumps each putting fuel into the cylinders). However, because the pressure is lower the fuel was not as warm as in a 'common rail' system, it is still noisy. However, performance is as good as common rail because 2 pumps at 800 bar mean as much fuel as 1 pump at 1600 bar. VW are now moving away from 'pump duse' as the ability of the system to undertake further developments is limited. Most VW group diesels above 4 cylinders are now common-rail.
Multijet is simply producing multiple (hence the name) squirts of smaller amounts of fuel per cycle of the piston (and crank). Bigger squirts of fuel create more of an explosion, hence more noise. Smaller (but more) squirts produce a smaller and quieter explosion.
The first common-rail diesel to the market was.... the Punto 1.9JTD.
Anyone bored yet?
p.s. Whether a car is turbo or not does not affect the method of combustion
Not bored, interested... thanks for that, all clever stuff.
Here is an overview and describtion of the engines in the latest Punto:
http://www.italiaspeed.com/new_models/new_models_2003/punto_2003/newmodels_punto_2003_02.html
http://www.italiaspeed.com/new_models/new_models_2003/punto_2003/newmodels_punto_2003_02.html
JTD Monkey
Member
Thank god for that, I thought from the lack of posting that everyone had died of boredom!
I think most of the audis definitley use common rail. The new 2.0 16v pd looks pretty good, shame it's a bit noisier than the common rails, but it is already putting out 168bhp in the passat, which I think makes it the highest bhp per litre for any diesel, though not if you include the new twin turbo 535d. Will be intersting to seat up the ante with a hot ibiza like they did with the 160pd. By far the quitest diesel I have heard is the Accord i-ctdi, may have something to do with a different compression ratio.
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While we're on the topic of diesels, can anyone clear up what good (if any) dump valves on TDIs do?! My mate at work is like- you've got to get a dump valve on your car now :nutter: but I dont think they sound too good on a diesel (pressure's too high) and im sure ive read they're a waste of time Are TDI's totally different to petrol turbos, and therefore cant use the same type of valves?
Im not thinking of getting one, I just want to be able to explain to my mate
Are TDI's totally different to petrol turbos, and therefore cant use the same type of valves?Im not thinking of getting one, I just want to be able to explain to my mate
JTD Monkey
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Not sure dump valves have any benefit to a 'normal' turbo car other than create a tasty noise. A dump valve is only of real use if the turbo runs at high-pressure (to release it quickly) but generally diesels don't run high-pressure turbos (there are exceptions, but they are very rare). Not sure I have come accross a dump-valve on a diesel before
The 1.9TDI engine in the Audi (VAG) range (A3, A3 Sportback, A4) is a 'pump duse' (also the 1.4TDI in the A2) but I think the new 2.0TDI is a common rail. There is a 160ps 1.9TDI in the Ibiza (I think it is a Cupra) for the 2006 model year but I think a lack of supply will rule-out the 168bhp 2.0 engine for a while. Audi's various 2.5, 2.7 and 3.0V6 TDI's are all common-rail now
The 1.9TDI engine in the Audi (VAG) range (A3, A3 Sportback, A4) is a 'pump duse' (also the 1.4TDI in the A2) but I think the new 2.0TDI is a common rail. There is a 160ps 1.9TDI in the Ibiza (I think it is a Cupra) for the 2006 model year but I think a lack of supply will rule-out the 168bhp 2.0 engine for a while. Audi's various 2.5, 2.7 and 3.0V6 TDI's are all common-rail now
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Are you sure diesels dont run at higher pressures? I think mine runs at around 1.3bar standard.....(1.9 TDIPD130); remapped up to 1.6bar. It also sounds like there is alot of pressure on acceleration.
Still wondering about the dump valves though, I havn't found an answer....
Still wondering about the dump valves though, I havn't found an answer....
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I searched for a bit of info on them last night and they do absolutely nothing. Purely for the noise on a TDI (which is apparently the next craze )
Who is the company in Blackpool? Do you know if they do remaps? :chin:
) Who is the company in Blackpool? Do you know if they do remaps? :chin:
wolfracepunto said:Still wondering about the dump valves though, I havn't found an answer....
It's been up before in the Stilo Tech forum:
https://www.fiatforum.com/showthread.php?t=27428
Hope it helps.
Just remembered
http://mav-tuning.co.uk/parts.htm
I wouldn't really invenst in a tuning company who's main selling point is fitting a bit of kit that has no improvement in performance other than attracting attention to yourself by the noise of a dump valve. Much prefer the stealth performance myself.
http://mav-tuning.co.uk/parts.htm
I wouldn't really invenst in a tuning company who's main selling point is fitting a bit of kit that has no improvement in performance other than attracting attention to yourself by the noise of a dump valve. Much prefer the stealth performance myself.
I now have a panda multijet, after someone wrote my punto multijet off, the 1.3 is a gem of an engine, really enjoy its surge of power, especially inthe punto, great for overtaking and the motorway, you have a rev counter keep it in the turbos power band, and enjoy this great little engine.
Decron
New member
While we're on the topic of diesels, can anyone clear up what good (if any) dump valves on TDIs do?! My mate at work is like- you've got to get a dump valve on your car now :nutter: but I dont think they sound too good on a diesel (pressure's too high) and im sure ive read they're a waste of time
Im not thinking of getting one, I just want to be able to explain to my mate
Dump valves on a JTD.... read this
https://www.fiatforum.com/punto-technical/130903-dump-valve.html?p=1371491
Despite what people say even the GSR kit won't defy the laws of physics and it will be a noisy waste of cash.
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Please expand on this?
Decron
New member
Apologies
I may have misread your post and then posted it wrong myself, for some reason confusing the GSR induction kit with a DV kit (It's not my fault, their website is awful ) However I wrote this massive reply and I am really pleased with it so I am going to post it anyway.A DV cannot increase performance. There is nothing for it to do other than go PSCHTTTTTTTT and unless it's perfectly actuated and it gets it spot on it will loose you boost pressure.
The boost pressure is generally highest on a diesel when the accelerator is on the floor and the engine is as max power, just before a gear change. If a dump valve is set to relieve the pressure just below max boost, it will sound similar to that on a petrol engine, but it will be dumping air while the engine is on power, not when the accelerator has just been released. All it can do is make the turbo less efficient. The wastegate tries to control the boost pressure and that will just increase the exhaust back pressure if the pressure is being dumped by a dump valve.
Now also figure in the fact the fact the JTD turbo is a VNT (GT1749V I belive if it's the 85bhp version) and this works works by adjusting the gas throat section at the inlet of the turbine wheel in order to optimize turbine power with the required flow velocity. At low engine speed and small gas flow, the turbocharger reduces the throat section, increasing turbine power and boost pressure. At full engine speed and high gas flow, the VNT increases the throat section, avoiding turbocharger overspeed and maintaining the booster pressure required by the engine. How do you think sticking a remote control hole (Which is what the valve is really) in the system will effect this? It will defeat the object totally and all it will do is work against it.
I would really like to see a dyno run of a standard car and the one fitted with a DV back to back. I think the run with the valve would show early boost loss and spikes where the VNT is struggling to compensate. The only way it could be perceived to increase performance is if you mapped around it which is pointless because you might as well have just mapped a standard engine
It's an expensive toy and about as useful as a catflap in a submarine.
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I know all that, I thought you were saying the GSR was a waste of cash...
It gives a similar sound with added performance benefits as opposed to decreasing performance like fitting a DV would do
It gives a similar sound with added performance benefits as opposed to decreasing performance like fitting a DV would do
