Now for the maths....which average?????? Do you add all the figures together and then divide by the number of figures.........or.....do you take the highest and the lowest figures and add them together and divide by two???

I think theres another way......brains a bit tired...but I think there are three ways....Mean, mode, median??????.....abit fuzzy I know!!! :S

Add all together and divide by number of runs

Thats where laws of physics (SOI vs. duration) ends and braking during coastdown starts.

Out of interest what is the most IQ you can inject without increasing SOI too far that the head pops off or fuel being injected is too far past TDC?

Find this topic really interesting as ive been reading recently about PD tuning with the EDC15. Also been looking/finding maps with my original file and PD150 files in winols.

As far as i have read on tdi club etc

Bigger bhp can be gained by increasing the injection cycle on the stock nozzles... Which is dangerous for the engine and creates super high egt's

Take a look a si's head... Cracked piston and head i believe

From my understanding. Please correct me if I'm wrong.

If the durations finishes after around 5-6degrees past TDC then this will cause smoke and higher EGT's due to the fuel not being able to burn ad the piston is on it's way back down.

If the start of injection timing is advanced (starts earlier) then this will increase peak cylinder pressure. Too much isn't good for the head. VAG fit stronger head bolts to the PD150/160's. I will look tonight to see what the differences of SOI is between a PD130,150,160.

The maximum duration is also limited to the cam. As it's the cam that controls the injectors.

Edited 8 July, 201114 yr by faboka vrs

The injector timing is electronically controlled, the PD cam simply pressurises the fuel dose held inside the unit injector like a big hypodermic syringe.

This is absolutely NOTHING like how a non-direct petrol injection system works so any received wisdom from cossie/scooby owners is likely to be utterly irrelevant.

However you can't open the injector too early or there won't be enough pressure to atomise the fuel properly and it'll lose power and smoke, so faboka is right, injector timing is effectively limited by the PD cam dwell around peak lift. The PD cam lobes are much bigger than the valvetrain cam lobes in order to increase that dwell.

The limitation of these fuel systems is the physical quantity of fuel held inside the unit injector, once you've injected ALL of that fuel then no more is available to make more torque so bigger turbos shoving more air in won't make a blind bit of difference.

Edited 8 July, 201114 yr by sepulchrave

Smart ******s lol where you learn all this? Would like to read up myself

The web is full of wonderful information. As are books.

Must sit down and take a read of the VAG self study book for the 1.9PD I came across.

Edited 8 July, 201114 yr by faboka vrs

I agree, a lot of vital information is thoughtlessly concealed in books and in "walls of text" on the internet.

Meh, tl;dr

Read the self study program last night for the 1.9PD. Interesting read about how the injectors work with the prime injection then the main injection.

Something I was wondering - and I'm not very clued up on the matter here:

Watching a video on a build thread of a '240+'bhp Fabia - it smoked like an old bus when it floored it.

Now, if the black smoke is unburnt fuel, and it's making over 240bhp, it's clearly injecting more than enough fuel is needed otherwise there'd be no smoke. (Is this correct so far?)

If that is the case, why can't the injectors go above 230? Is there another limiting factor besides total injected fuel, or am I taking an overly simplistic view to things? Because otherwise surely the 240 car wouldn't be injecting enough fuel to smoke in the first place?

CT17, are you able to log channel 4 on vcds? This would show us your SOI and duration.

Something I was wondering - and I'm not very clued up on the matter here:

Watching a video on a build thread of a '240+'bhp Fabia - it smoked like an old bus when it floored it.

Now, if the black smoke is unburnt fuel, and it's making over 240bhp, it's clearly injecting more than enough fuel is needed otherwise there'd be no smoke. (Is this correct so far?)

If that is the case, why can't the injectors go above 230? Is there another limiting factor besides total injected fuel, or am I taking an overly simplistic view to things? Because otherwise surely the 240 car wouldn't be injecting enough fuel to smoke in the first place?

The 240bhp could make any other figure on any other rollers though. I wouldn't be surprised to see 210bhp or even 260bhp...

I think that there is a basic misunderstanding here about BHP measured at the wheels and the notional flywheel BHP which is the one people always quote because it is a higher number.

Unless you rip the engine out of your car and install it on a testbed to develop it, then the 240+ BHP is a complete guess based upon the power measured at the wheels, this is why you see such wildly fluctuating figures depending on which dyno and who did the maths.

The reason for the smoke is that the mapping is crude, when you fit a larger turbo you introduce a pronounced step in torque output and in order to make the transition many tuners just chuck in a load of fuel to prevent leaning as the boost rushes in.

Bear in mind that BHP is Torque x RPM, so you can increase one or the other or both to increase BHP, put simply naturally aspirated engines do it with RPM, turbo engines do it with torque, but with diesel you cannot increase RPM significantly because you cannot control the ignition point like you can with petrol.

Thus direct injector timing is the only control you have over the ignition point and there are considerable limitations as already mentioned.

The reason for the smoke is that the mapping is crude, when you fit a larger turbo you introduce a pronounced step in torque output and in order to make the transition many tuners just chuck in a load of fuel to prevent leaning as the boost rushes in.

I'm not sure I follow with this. Yeah bigger turbo means more air being sucked into the engine. So we are able to inject more fuel to keep the same AFR so we get more torque/power. This to me is not crude, its simply maths.

To get more fuel the the injector duration needs to be increased to meet the required injection quantity. Now what is crude is that with some maps, the duration is increase so much that it ends too far past top dead centre which causes smoke as the fuel is unable to burned due to the piston now being on it's downward stroke. This can be reduced by increasing start of injection. But overall their is a limit to how far you can increase start of injection, total duration length and also the cam.

So when people assume that if it smoke theirs stil room for more power is *******s

CT17, are you able to log channel 4 on vcds? This would show us your SOI and duration.

No, are you speaking english?

Ask me about Land Rovers and I'm fine, but not so up on VAG products.

I'm not sure I follow with this. Yeah bigger turbo means more air being sucked into the engine. So we are able to inject more fuel to keep the same AFR so we get more torque/power. This to me is not crude, its simply maths.

Yes but, think about the transition, we go from a low fuel requirement to a very high fuel requirement very suddenly and the requirement continues to climb very quickly until peak torque is reached. This is difficult to map for without a high resolution standalone ECU.

Drag tuners often use constant flow secondary injectors activated when the blower starts boosting, crude but effective and it allows them to map the primary injectors to fine tune the mixture.

Yes but, think about the transition, we go from a low fuel requirement to a very high fuel requirement very suddenly and the requirement continues to climb very quickly until peak torque is reached. This is difficult to map for without a high resolution standalone ECU.

From the maps I've been looking at this week, I wouldn't say it's a big increase at all. Yes their would be a larger increase higher up the rev range. But at around 2krpm I wouldn't agree. Infect the default driver wish map goes all the way to 70mg. It's only the torque limter and smoke map that limits it to around 52mg (guess as I can't remember of the top of my head)

Anyway instill don't understand why this increase fuel would cause smoke?

No, are you speaking english?

Ask me about Land Rovers and I'm fine, but not so up on VAG products.

Lol

VCDS (vag-com) is a diagnostic logging software. You can use it to record data from the ecu. Rpm, intake temp, fuel temp etc etc.

So what about the weight of the person driving the car?

We all talk about the weight of the back seats, spare wheel etc, bigger turbo and so on but what if one driver is 14 stone and the other is 10 stone both driving identical horse power cars.

The 10 stone man would win in a drag. Yes?

So the 14 stone man would need more horse power to win (and it would smoke more due to heavier load).

Horse jockies are feather lite for a reason.

As far as i have read on tdi club etc

Bigger bhp can be gained by increasing the injection cycle on the stock nozzles... Which is dangerous for the engine and creates super high egt's

Take a look a si's head... Cracked piston and head i believe

Yarp, old cracked head sold on eBay for £11.50, more than scrap value haha