Intercooled turbo diesel intake resonator, reduced turbo lag maybe?

[Tesla]

I'm talking about the resonator which is normally positioned just after air filter as a branch off the main air intake tube.

In normally aspirated vehicles it often has a dual function, noise reduction and also to improve efficiency of air intake into cylinders by bouncing pressure pulses between the intake valves and the resonator.
In my case I have a turbo, intercooler and about 5' of contorted tubing in between, so I doubt that there is any coherent pressure pulses going on and always just assumed it was there to just reduce intake noise.

Recently I had reason to put a large 4litre chamber in the PCV blow by line, like a catch can, which connects into the intake just after the resonator, seat of the pants assessment indicated a reduction in turbo lag. This was interesting as the mod was just for diagnostic purposes not for performance so the apparant change was a bit of a surprise. I still need to re jig the setup so I can switch between extra chamber and no chamber on the fly to confirm there is a distinct change in behaviour.

In a diesel the air filter is the biggest restriction in the induction line and hence there is always a some vacuum behind the filter which increases with rpm & load.
The effect that I believe is occuring is basically to create an additional volume of induction air between the filter and turbo, when you accelerate from low rpm the injection fuels up, the exhaust then needs to spin up the turbo to push more air in to the cylinders, hence more exhaust and more air again and the turbo spools up. Initially there is a dramatic increase in vacuum in the intake infront of turbo, effectively the engine takes a big gulp of air, but has trouble getting more until turbo gets up to speed and we have turbo lag.

Having a greater volume of air between filter and turbo reduces the rate at which vacuum increases and hence provides more air to engine at that initial point of acceleration, hence allowing turbo to spool up just a bit quicker. The extra volume does not affect steady state running, it only comes into play when there is a change in intake vacuum, MAF is positioned before this air reservoir so under initial acceleration it will, run the engine marginally leaner as MAF will be reading lower airflow than engine is actually getting and on deceleration it will run marginally richer as vacuum is reduced and the reservoir volume is replenished. I don't think that is too much of an issue as acceleration is usually a rapid response whereas on deceleration pedal action is usually more gradual and feathered down as desired speed is reached.

It may have a beneficial effect on economy by moderating down driver behaviour if vehicle response is more effective, i.e. less overkill on pedal required because lag between action and response is reduced.

I'm going to play with this a bit, just want some input as there may be other things I have not considered.
Thanks in advance.

ps - I already have a ram air type of setup on intake which has a beneficial effect on economy by reducing intake vacuum and also partial front skirt, grill block and no radiator fan, have tried wheel covers, no benefit in my case.

[oil pan 4]

Have you considered finding the largest affordable air filter that you can possibly fit under the hood and building an air cleaner for it and installing it?
Possibly to the point of relocating a battery, coolant or windshield washer bottle?

[Tesla]

Was hoping you'd pop up.

Yes have considered that, but that's major work, stock filter is as big as box will take, not willing to go to high flow (aka dust flow), have thought about a custom filter box to take double stacked stock filters, but would require major modifications under bonnet.

I'm not really after more power, just looking at tweaks to improve driveability and maybe some economy benefits.

Do you think my logic is sound regarding turbo lag and having some sort of air reservoir post filter.

Just had another thought, there is also a secondary resonator box directly below filter, if I tapped into this, then the reservoir would be pre MAF and would not change fueling at all, still need to actually confirm there is a real change, it only is that second or two after accelerator is pressed, after that she pulls far more than I need anyway.
Maybe I could use that as a remote supplimentary filter inlet instead, another possibility.

[Tesla]

I've done a more permanent set up and I'm looking for test method ideas to determine if improvements are real or placebo.
The “seat of the pants” dyno say’s yes but I’d like something more quantifiable.
I'll probably be keeping it in for a while, so will see if there is an improved fuel economy over next few tanks, but for now just want to determine if there has been an improvement in engine response time.

The mod is only for the immediate period after throttle is actuated to get a quicker response from engine for standing starts and overtaking and does not change overall boost, power etc at status quo when cruising etc.
One thing I thought of is doing controlled runs on a straight stretch of road from 2nd gear to 5th, starting test at specific rpm with gear changes at designated rpm’s and full throttle application after each gear change. I thought setting designated rpm’s at lower end of scale would test better if there is an improvement and finishing test when set speed is reached and noting total test time.
Wondering if anyone has other ideas I could look at.

[oil pan 4]

I don't think its a bad idea.
Since I relocated batteries and the coolant tank to make room for the air cleaner and piping I was able to construct the intake for my suburban the way I wanted it, no compromises, using the biggest air filter I felt I could easily get ahold of for a reasonable price, STP SA8037 air filter and since I always like to have a backup plan as an alternative I can use a slightly smaller SA8038 in a pinch (I think the 8037 fits newer dodge diesels and the 8037 fits newer gas trucks of an unknown make).

Basic lay out of my air intake is a lot like yours, ram air with a long run between air filter and the inlet of the turbocharger.
I also went out of my way to use 4 inch piping between the air filter and turbocharger as opposed 3'' pipe which would have been much easier to run.

A larger free flowing intake will not hurt a diesel at all.

[AndrzejM]

Interesting thread. Subscribed.

[Tesla]

oil pan 4

I'd like to put a larger diameter intake on it, you've done well to go from 3" to 4", in terms of cross sectional area that is nearly double, mine is just under 3" at filter box, tapering down to about 2" at turbo inlet, the problem is all the attachments, pcv, resonator and in particular MAF are all on this section, to go to a larger section will likely play havoc with MAF, so I'm looking to what I can add to the periphery and before filter and have a few more ideas yet.
Getting positive pressure to airbox from front of vehicle using the ram setup netted around 0.5l/100km around 5% improvement for me, more power and better driveability.

Did a small round of tests and added a small air bleed in, post MAF (around 4% more air)to run a bit leaner, the test results were good and bad.
I decided to do simple acceleration test full throttle 4th gear from 60km(40mi) to 90km/hr(55mi/hr), didn't want to mash through gears at full throttle and staying below boost limmiter rpm.

The total results were very similar for with and without mod, if anything without was marginally faster, that was the bad.
The good was that the vehicle with mod in was faster in the first half (60-75km/hr) of the acceleration test, but lost ground in the second half (75-90km/hr), whereas without mod it lagged in first half, but kicked in in second half of test, so "seat of the pant's" dyno wasn't wrong.

The mod gave more power lower down but less power at the upper end, acceleration was quite smooth right through and spool up seemed to be a bit quicker.
Averaged numbers were
with mod , total 10.05 sec, 1st half 5.00, 2nd half 4.95
without mod, total 9.80, 1st half 5.35, 2nd half 4.45

I'm due for a tank re fill so will try to stop playing and run out a full tank with current setup and see if economy improves.

I suspect the loss in the top end is due to lower fueling by MAF because of unmetered air.