Going back to Standard CDti Air Duct

[rovexCDTi]

I would expect it to adapt to the amount of air going in to make the best ratio. Even if it doesnt and the flow doesnt really help as far as the MAF goes it doesnt actually change anything in this discussion. Air flow is more than just about the MAF. It effects the turbo and the air temperature more than the MAF.

[Ross R75]

Originally Posted by BigRuss

Ok here's a question for you all what do you expect that would happen to the airflow figures as measured by the Maf when you remove the air filter or put on a through flow sports air filter?

Russ

Russ, I would expect to see less air passing over the sensor because it will see a drop in cooling effect due to a drop in intake air velocity. Consequently, less fuel will be injected and performance will actually drop.

[rovexCDTi]

Nice theory, but not the case in reality. The turbo spools slightly quicker increasing velocity, even if the end result is less fuel, the improvents in spooling and reduction of intake charge temperature more than compensates.

The results speak for themselves, less black smoke and more response is not a placebo. The turbo does spool faster, its measurable with a boost gauge.

The Synergy, pierberg Maff and intake mod certainly works, even if its quick and dirty. Im sure the 160 MAP is better, but its relatively new and not much good to those of use 250 miles from the nearest programmer.

[BigRuss]

Originally Posted by Ross R75

Russ, I would expect to see less air passing over the sensor because it will see a drop in cooling effect due to a drop in intake air velocity. Consequently, less fuel will be injected and performance will actually drop.

Correct

The airflow figure will drop, in the case of a totally inspec maf it will be well below the minimum of 440 mg per stroke at idle fully warm egr closed
The airflow is reduced across the entire rev range and performance will be adversely effected.

Russ

[Ross R75]

Originally Posted by rovexCDTi

Nice theory, but not the case in reality. The turbo spools slightly quicker increasing velocity, even if the end result is less fuel, the improvents in spooling and reduction of intake charge temperature more than compensates.

The intake tract upstream of the turbo has no effect on its ability to spool unless its almost blocked. There's no difference whatsoever in the acceleration of the turbine. I'd strongly suggest that any discernible drop in intake air temperature (there is none) would be completely negated by the fact that its just about to be forced through turbine vanes doing in excess of 50000rpm and then shoved through a very restrictive intercooler. There is no benefit to removing the air intake ducting, period.

[rovexCDTi]

Originally Posted by Ross R75

The intake tract upstream of the turbo has no effect on its ability to spool unless its almost blocked. There's no difference whatsoever in the acceleration of the turbine. I'd strongly suggest that any discernible drop in intake air temperature (there is none) would be completely negated by the fact that its just about to be forced through turbine vanes doing in excess of 50000rpm and then shoved through a very restrictive intercooler. There is no benefit to removing the air intake ducting, period.

Evidence? I have evidence to the contrary with my measured boost levels. With no other changes the boost is higher earlier with a modified intake.

Why would the intake velocity drop? The engine is still demanding the same amount of air and its still passing through the same space around the MAFF in the same time frame.

Where is the evidence for the reduction in velocity?

If the air is cooler, and it is, the volume of air is the same, but the available oxygen is higher. The fact that the turbo heats it isn't relevant.

[BigRuss]

The engine can demand as much air as it likes but unless the maf sees the airflow as being correct for the revs and engine load it won't allow the correct amount of fuel to be injected to obtain the optimum fuel air ratio.

If the intercooler o rings have gone the airflow signal increases and the maf readings are above the max level of 500 mg a stroke at idle.

So change things one side of the maf the airflow drops the other it increases

Maintaining the correct airflow and hence fuelling can be a tricky business, without being able to verify any modifications by being able to look at the airflow figures there is no way of knowing if it's correct or not
Just because it feels better than it did doesn't mean it's correct.

Russ

[rovexCDTi]

Again theory, but where is the evidence that this actually happens? why does a slightly freer flow of air before the aperture the MAFF sits in reduce air flow? The engine is still demanding the same volume of air through the same aperture. The intercooler O rings are a totally different story and irrelevant to this discussion.

If it feels better I couldn't care less if its 'correct' or not.

[Ross R75]

Originally Posted by rovexCDTi

Evidence? I have evidence to the contrary with my measured boost levels. With no other changes the boost is higher earlier with a modified intake.

Why would the intake velocity drop? The engine is still demanding the same amount of air and its still passing through the same space around the MAFF in the same time frame.

Where is the evidence for the reduction in velocity?

Christian,

I've been actively building and tuning turbocharged petrol and diesel engines for the last 18 years. I'm far from being the font of all knowledge when it comes to the M47R engine but I've owned and fettled with them for 10 years now, owning and running 5 of them over the same time period.

Russ and Brian know all there is to know about the MAF vs fuel and injector duration mapping, they map them every single day. Brian developed the 2nd generation CDTi ECU and refurbishes them for X-Part.

The theory and practical reality as to why a modified intake cannot make any difference to the point at which the turbocharger starts to produce pressurised charge air, or the pressure that said charge air peaks at, is very simple. The charge air tract volume downstream of the turbocharger is finite and is a larger restriction in the system than the intake tract upstream of the turbocharger. Have a look at the width of the intercooler outlet elbow if you need a reference, it's far smaller than either the intake ducting, or the MAF chamber. Put a straw in your mouth and drink out of a pint glass. Try the same with a shot glass. You can't drink faster from the pint glass because the width of the straw is the same under each scenario. The theory and reality is exactly the same in your charge air system.

Originally Posted by rovexCDTi

If the air is cooler, and it is, the volume of air is the same, but the available oxygen is higher. The fact that the turbo heats it isn't relevant.

It doesn't matter. The MAF governs the fueling and it doesn't work in the way you're thinking it does. It heats a wire (effectively a resistor) between two poles on the tip of the MAF probe and attempts to keep it at a set temperature. The MAF sensor reports the voltage required to maintain temperature to the ECU and the ECU cross references this voltage with a given value in the fueling map table, engine revolution table, injector duration table and a host of other variables. The point to take away from this, is that the MAF doesn't measure the temperature of the intake air, it simply measures the cooling effect of the intake air over the heated wire. In this scenario, air velocity matters just as much as air temperature. Again, imagine blowing gently through a straw, then repeat the process with the same force using a kitchen roll tube. The velocity of the air through the kitchen roll tube is far slower because the volume is greater, it's cooling effect is consequently reduced. The scenario is almost identical to that of the MAF with a larger volume intake.

I've tried every imaginable combination of air intake, maf compensator, egr mods, decats and tuning boxes on the M47R. As far as intakes are concerned, the best one is the way that the car left Longbridge or Cowley.

[rovexCDTi]

Ok on the first point, even if my results arent agreeing in practice, but the second point is mute since you aren't effecting the size of the 'straw' because you havent changed the size of the aperture the MAFF sits in. Everything from the air box onwards is the same.

If you enlarge everything I agree with you, but you arent.

For me the air intake was never about ultimate power, it was about response and temperature. It feels more responsive and the temp is lower (very slightly), according to whats reported by Torque (on my phone)