For many years I have considered extending the air filter intake pipe on my 1973 350SLC to allow the engine to inhale cold air (ie. a true cold air intake) as is the situation with newer models. I have finally just completed this modification and am very pleased with the results.

My 107 has the high compression 3.5 litre M116 fitted with D-Jetronic injection and is rated at 147kW or 200HP DIN (230HP gross SAE). The air filter intake pipe has its opening just forward of and above the alternator. It draws air from within the engine bay which can be hot having passed through the radiator. The intake pipe tapers down to about 75mm (3") diameter at its mouth.

I cut my intake pipe back almost to the bend such that an 80mm (3.15") diameter spiral reinforced hose could be pushed on and clamped with a large hose clamp. The intake air temperature sensor needed to be relocated slightly closer to the air filter as it was originally located on the section I cut away. The other end of the flexible hose attaches to a short length of 80mm diameter aluminium pipe which passes at a downward angle through an aluminium panel I fabricated which fits between the radiator side support and the side of the engine bay. I flared the front end of the aluminium pipe to create a smooth bell mouth. All this sits behind the panel between the oil cooler and the right headlight behind the grille. This panel already had some openings however I added more. The voltage regulator for the alternator being mounted on this panel was in the way so I relocated this to the rear of the new panel I added.

The original reason for all this was in the hope of a little more power at full throttle and high engine speeds (as I am planning to use it for a little motor sport). Whilst the high compression 350SLC offered good performance in its day, by today's standards it is nothing special. Following the modification I have noticed the engine revs to the redline faster through the gears (suggesting a power increase). Previously the engine was lacking air at full throttle with a hint of black exhaust smoke as redline was approached. There is no sign of black smoke following the modification. An unexpected benefit is improved throttle response and no pinging (detonation). This engine with its 9.5:1 copression ratio requires minimum 98RON fuel. With reduced fuel quality and the elimination of tetra-ethyl lead in recent years I have found that with the ignition timing set per factory specification, it was suffering from pinging under load. With the cold air intake this problem has been eliminated.

Whilst the high compression M116 (3.5 and 350) was not common in some markets, particularly North America, and the lower compression M117 (4.5 and 450) may not suffer with pinging, the M117 may still benefit from this modification in that it allows for a greater volume of colder air. A similar modification could possibly also be performed on W108/W109 (280/300 SE(L) 3.5/4.5) and W116 (350/450 SE(L)) cars which also used the D-Jetronic versions of the M116 and M117. If there is sufficient interest, I will take some photos of the modification.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Hi Greg,

Sounds very interesting. Pictures will be great but I also hope you bring the car to the next MBCNSW meeting to have a better look.

Did you consider adding a vent or scoop to the bonnet? I have seen this done on a few W116 with the M116 and M117 engines.

Cheers,
Michael

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http://www.w116.org
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Greg, we need a picture of this very important modification.

i dynoed my w109 3.5 with and without the aircleaner, it lost about 3-5 hp without the air cleaner installed, suprisingly. although making the inlet larger and putting it in a coler place, is always good

mike

Michael (w116.org),
Will bring it to next week's meeting if you want to see it. Oh, and I hate to disappoint, but the bonnet scoop won't be happening!

tosbt,
Pictures will come but will have to wait at least until after next weekend. For those who may want to try the same on their 107, I will also scan a drawing of the extra panel I fabricated.

Mike (j9fd3s),
I am not all that surprised power would drop with air filter removed. Air into throttle body would be both hot and turbulant. Air filter assembly on D-Jet M116 and 117 at least provides a reasonable flared mouth for the throttle body which should provide good air flow, unfortunately still with hot air from within the engine bay. My mod allows cold air through a slightly larger intake pipe to the original air filter assembly. I would be surprised if it does not allow for maybe a 5hp increase (perhaps even more at speed on the road with the benefit of the higher air pressure behind the grill). In my case the nicest benefit was eliminating pinging (detonation or knock) with the ignition timing set where it should be. This in itself improves throttle response and acceleration.

Greg

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Parts required:
1. Original air filter assembly with intake pipe shortened to join (you will notice I used the oportunity for a fresh coat of paint). The removed section (not re-painted) is visible. The air temperature sensor needs to be relocated from the removed section to a section of the intake pipe that is to be retained. It can be fitted through an additional hole and secured with a nut.
2. Suitable length of 80mm I.D. spiral reinforced flexible hose.
3. Hose clamp to attach hose to air filter intake pipe.
4. Additional panel to ensure cold air is drawn from forward of radiator, oil cooler and condenser. The panel shown is to suit my W107.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Closer view of the front of the additional aluminium panel. Note the bell mouth of the intake pipe to ensure best air flow. The intake pipe is 80mm O.D. aluminium tube and is bonded to the panel with epoxy resin (the small screw retains the pipe until the epoxy cures).

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Closer view of the rear of the additional panel. Note the relocated alternator voltage regulator which otherwise would have obstructed air flow to the cold air intake.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The region where the panel is to be located. Note the 5 additional 35mm diameter holes to allow sufficient air flow.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The additional panel installed.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Front view showing the 5 additional 35mm diameter holes. The bell mouth of the intake pipe is visible through the holes.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The flexible hose is fitted. Only the end attached to the air filter need be clamped.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

View from the opposite side of the engine.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

View from the front.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

All finished! With the bonnet (sorry... hood) shut no one will ever notice. The performance benefits though.

Attached Thumbnails

 

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.