W210 airbox modification thread
 

Hi all,

I have decided to post up a thread which will be more of a R&D experiment with my E300 project. I am going to be doing modifications to the stock airbox on my W210 to see what the differences are with different setups and the best route for any performance gains over and above the stock setup.

Firstly here are some specs on the stock setup - basically everything feeding into the turbo:

• Airbox overall is very large, unfiltered air enters the bottom of the air box, through the filter then through the pipework to the turbo via the top of the air box.
  
• The MAF is connected to the airbox via a rigid pipe - its a large 3" pipe diameter
  
• The MAF pipe inside the top of the airbox has radius bends like a velocity stack for smooth airflow
  
• The pipe between the MAF goes from the 3" (78mm) to 60mm which connects onto the turbo
  
• There is a crank case breather line attached just after the MAF introducing oily fumes into the inlet
  
• The bottom of the airbox is a round 3.5" intake
  
• This is then attached to a small 90 degree connector into the front facing air intake
  
• The air intake slot is front facing, between the headlight and the radiator - it is rectangular and around 2.5" by around 4"
  
• The front facing air intake sits behind the the bonnet next to the grill (but not actually behind the grill)
  
• There is probably around 1-2" gap between the front of the bonnet and the air intake

Here are my comments on what is good about this setup:

• The stock airbox should be large enough to accommodate quite a bit of power
• The MAF is large and has a good radius for flow
• The large 3.5" inlet should be able to supply the engine with plenty of air to the bottom of the airbox
• The airbox is well situated away as far away from the exhaust tucked into the wing

Here are my comments on what could be improved:

• The pipework from the airbox could be improved as it is corrugated rubber
• The front facing air intake is a restriction - the WHOLE engine is breathing through a 2" X 4" hole
• Vented crankcase gasses could interfere with the air flow

Here is the issue I have with the front facing air intake:

To get to the airbox the air must:

• Hit the front of the car and go through the grill
• Go around a 90 degree bend to the front of the intake between the back of the bonnet and the front of the radiator (bonnet blocks direct flow)
• Go around another 90 degree bend into the small rectangular slot
• Drop down 90 degrees down the back of the headlight
• Turn another 90 degrees into the plastic elbow at the bottom of the airbox

I have just gone out and simply removed the small 90 degree plastic piece between the front facing air intake and the bottom of the air box, I have just test driven it and this is what I have found:

• Increased throttle response - no lag in pressing the throttle and movement unlike before (eg pulling out of junctions)
• Smoother changes in gear
• Smoother idle
• No real increase in induction noise around town or on the motorway
• Better low down torque - power feels more linear rather than sudden
• Boost pressure builds more predictably

Please be aware that the whole engine is bone stock, it is running a new PAPER air filter which again highlights how the drop in 'performance' air filters aren't necessarily going to give increases in performance.

This is just an initial test, I will get up some photos soon for everyone to comment, so far its cost me nothing and I have performance gains. I am aware that the engine will be sucking in slightly warmer air, however the stock air box is well out of the way and there is plenty of air flow around that side of the engine bay. I have also kept the stock front facing air intake so that would also supply some fresher air towards the intake area. The bottom of the stock airbox actually sits on the side of the engine bay and is shielded from any water from the road.

Here are a few things I am thinking about testing out:

• Larger cold air intake replacing the stock intake to sit between the radiator and headlight
• Hard pipe between MAF and turbo
• Catch tank for oil fumes from crankcase
• Metallic tape on the engine side of the air box to reflect heat
  [*}Possible additional air feeds to the side of the airbox

I might also try:

• Drop in 'performance' air filter
• Cone filter sitting inside the stock air box
• Enclosed filter replacing stock air box

First update on this, just driven to work with the small connector removed, throttle response is much better and overtaking is better as the engine now gets the additional air when it demands it easier.

There is a slight increase in induction noise when accelerating however not the usual induction roar - I guess its because the turbo is quite small so isn't pulling as much air!

Second update, I have now replaced the airbox with a standard generic induction kit filter, there has been an improvement in throttle response as well as overall smooth running of the engine.

The car now picks up better from a standstill and the shifts seem smoother, also the boost builds up much smoother and quicker than before.

You can hear the additional air coming into the engine and when you let off the throttle you can hear the turbo spool down - although it sounds like a blow off/recirc valve I know diesels don't have them.

I will report back with my findings with fitting a generic induction kit filter to the stock setup, it seems that the stock box is slightly restrictive at the lower end.

Could you attach pics of your setup? Thanks!

Sure thing, I have just got around to taking a photo of the setup, its not 100% there yet as I still need to fabricate brackets and heat shields so its for a test:

The stock air box is massive so there is a lot of space on that side, one thing to note is that you need to move the turbo vacuum transducer as that is attached to the airbox as well, I think I simply reused the bracket and attached it elsewhere:

http://i93.photobucket.com/albums/l4...psvfluqoby.jpg

http://i93.photobucket.com/albums/l4...psc5lo3u8w.jpg

Eliminating twists and turns is always beneficial to intake and exhaust systems, as is smoothing out the piping in those areas so the pipes are slippery to air. If you can modify the intake so that it takes in ram air from the front, has minimal bends, is smooth inside, and isn't gummed up with soot from the EGR, you'll be golden.

I will be getting a catchcan for the oil vapors from the rocker cover, I will then be able to simply add a 3" pipe from the filter to the turbo as a straight shot - the issue is that there isn't really much frontal area free owing to the radiator but I will see what I can do as a good route, just need to get a catch can, then I can simply replace the whole lot.

Yep, a catch can full of fine steel wool will catch all the oil and you can put a small breather filter on the can of you want to eliminate the extra port on the intake altogether.

Just need to find one with large enough ports, I think the pipe is something like 17mm, its next on the list though, will be interesting to see how much difference a straighter inlet hose will make - its almost in the stock position at the moment, just with a different air filter.

very interested in these mods

please keep us to date and with pics of everything

thanks

Will do, I noticed that the car was built for quiet running rather than performance (although it was the fastest diesel production car when it came out) - I noticed that it had a HUGE airbox, but quite a restrictive inlet and a massive exhaust backbox which had the pipes doing a full 180 inside.

You should notice a difference if you simply remove the plastic joiner between the front air feed (which is behind the solid part of the bonnet) and the airbox.

Hi, nice work! This is an area I was eventually going to address so I'll give you one of the thoughts I had.

You can remove the MAF sensor altogether and eliminate it with a resistor in the circuit. This will further increase flow. In the event you need to keep the sensor in place for visual inspection/emissions reasons, you can fabricate a larger tube and install the sensor in the side.

The MAF sensor tube is 3" in diameter, on the Nissan Skyline they upgrade to a Nissan 300ZX MAF which is 3" to allow for enough flow for 1000bhp. The MAF and airbox are actually fairly massive - its just the small front facing/partly blocked intake feed next to the radiator which seems to let the car down.

The MAF sensor would also need to be in the same sized tube to get the correct measurement of air flow. I am not sure what else the MAF on the diesel engine is being used for apart from the EGR, I am guessing it would adjust fueling slightly but it does also have the MAP sensor and the intake temp sensor to calculate the air density.

Once I get a catch tank sorted I will look into modifying the inlet a bit more, will look to simply fit a straight 3" pipe to the turbo (with a reducer to 60mm) and attach the MAF and filter as is to see what difference it makes.

On the stock turbo I don't think it will make a huge difference, however I am thinking that it would make a bit of difference when there is a larger turbo requiring additional flow.

One thing to keep in mind is that a diesel operates with AFR's of as much as 32:1 so they require a boatload more air to build the same HP as an equivalent petrol engine.

Its why I went with a GT35 with higher boost vs a GT45 with lower boost for the same volume of air - might try out both and see what happens though!