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I've removed the inlet plenum on my SDI...


mk2
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OMG. I now completely get why people block off the EGR valve. I'll have to post some pics for you to believe what I'm seeing. A-maz-ing.

The base of the inlet trumpets are so clogged I'd say that the diameter of the air flow duct is only about 10mm instead of 30. Who knows how bad the back of the inlet valves are. I know that the inlet ducts (leading to the inlet valves) are really bady clogged with soot. Hard gritty material it is.

I thought that it may have something to do with the blow-by gasses, but there isn't that much oil residue in the back of the plenum chamber. I'll be bunging that up for sure and adding an open air vent.

Looking at the way the gasses flow in this head, I think adding short ducting tubes into the inlet manifold will be more beneficial than a blanking plate at the end of the exhaust gas gallery. Having that gallery at the base of the trumpet completely defeats the purpose of the resonant air flow. I reckon EGR on this head is an afterthought.

I need to figure out how to very carefully scrape out the soot from the inlet ducts, without too much going into the cylinders. Any suggestions welcome!

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You could try a hoover?

Is your carbon dry and hard or thick, moist and gunky? I believe on the Tdi the CCV adds oil to the manifold making the hot dryish carbon stick to that and the rest is history.

Check out the elephant mod and see if it would work on the Sdi? Someone told it me it might not for some reason but IMO turbo or not diesels work pretty much the same way. Regarding the EGR being an after that I bet it was.

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Thanks FKA daood. Yeah the stuff is quite dry. Vacuum cleaner.... Mmmm there's an idea.

I guess i could vacuum and scrape at the same time. I could do it with both valves open, so any airflow (and gunge) would simply be sucked through.

I'll get the camera out before starting work.

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I don't really know the ins and outs of an Sdi so I can't help much so maybe pm Skezza as he is the Sdi man lol,

Your lucky in away its that drive stuff but cleaning it is still a pain. What about a baby bottle/chimney sweep style brush?

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This afternoon I started...

I ended up removing the inlet manifold in the end as I came to the conclusion that that would be the easiest way to do it. Now clean again. No trace of carbon buildup now. First clean with parrafin/kerosene then finish with cellulose thinners. Thinners are excellent at cleaning off diesel deposits by the way!

And once clean and on the bench it became clear how the design really has been messed up by the emissions team at VW. Under the tumpet bases there are little oil drains (for when the plenum fills up with oil), which also messes up the sensitive air flow.

So now my plan is to fill those gaps with high temp silicone (as used for gaskets) and smooth everything off.

Also insetad of fitting a blanking plate to the EGR, I'm going to plug each individual gas duct that joins on to the exhaust gas feed gallery. How I'm going to do that is yet to be decided. I was thinking of either tapping the holes and filling them with bolts, which I could die grind off later (to not affect the air flow), or machine up some ali plugs (same diameter as the holes) and then simply wedge them in and grind off later. I'm tempted to go down the ali rod route as it's probably easier....

I'll take some pics in the morning.

Edited by mk2
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I'll be watching this with interest, I started down the same route just the other day but ran out of time, I also couldn't figure how to remove the unit attached to the right of the manifold, I could have split the breather pipe but thought better of it. It looked simple enough, one allen headed bolt and a single nut, but once the nut was off the unit wouldn't budge, any thoughts?

Please get those pictures up I'm a numpty and need all the assistance I can get!

Cheers

Ian

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Some pics as promised... :)

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I have got to say that the engine will have to run better once I've done the mods. I mean, just look at all the cr@p that bungs up the inlet. Any restriction on flow will not be noticed and the computer will still supply the same amount of fuel per cycle as if it is running clear. So the exhaust gas will always be sooty. Running rich. I have no words... Economy should be better, power better, emissions better. The oil wont need changing as often. The cylinder bores will stay cleaner.

In addition to the blocking off of the EGR ducts, I've already diverted the blowby gasses down on to the road below the car.

I'll report back if it makes any difference when it's all back together again.

Edited by mk2
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I'll be watching this with interest, I started down the same route just the other day but ran out of time, I also couldn't figure how to remove the unit attached to the right of the manifold, I could have split the breather pipe but thought better of it. It looked simple enough, one allen headed bolt and a single nut, but once the nut was off the unit wouldn't budge, any thoughts?

Please get those pictures up I'm a numpty and need all the assistance I can get!

Cheers

Ian

Ian, look at my clutch heat shield thread. There's a pic there that may help... The EGR unit has two mounts. The top one is easy- just a nut- the lower one has a nut and a pedestal that you need to use a 13mm stud extractor to remove it (or a pair of mole grips). Just keep the dip stick tube out of the way while working. Remove the pedestal before the top nut.

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Ian, look at my clutch heat shield thread. There's a pic there that may help... The EGR unit has two mounts. The top one is easy- just a nut- the lower one has a nut and a pedestal that you need to use a 13mm stud extractor to remove it (or a pair of mole grips). Just keep the dip stick tube out of the way while working. Remove the pedestal before the top nut.

Ah yes that makes sense! I'll be giving that a go in the near future, my inlets are as badly fouled up as yours, so I'll be looking forward to better running too! Are you putting the trumpets (restrictors?) back?

Cheers

Ian

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Me too, would a step by step guide be too much to ask for the un-trained like me? :)

I don't think there's much to it. IM is just held on by four big allen bolts isn't it? Then it's a case of actually getting it on because if it's anything like mine, it's been baked on I imagine.

Cleaning it is an art in itself. There's a guy on the Internet who cleans them using a flamethrower lol, but I follow a really good VW video blog called BMAC VAGS and they clean them with plain ordinary Mr Muscle. They spray Mr Muscle in all of them inlet pipes, leave it to agitate with the carbon then spray the manifold using a jet washer.

Youtube Video ->

Original Video

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Ah yes that makes sense! I'll be giving that a go in the near future, my inlets are as badly fouled up as yours, so I'll be looking forward to better running too! Are you putting the trumpets (restrictors?) back?

Cheers

Ian

You absolutely need those trumpets. They are there to set up a resonance or pulse wave to increase the air flow going into each cylinder. If you leave them off, you lose lots of power. The length of each trumpet is precisely tuned to give you peak power in conjunction with cam valve angles. short trumpets give you more power at high revs and no low end torque. long the opposite. somewhere in the middle is the best compromise for general driving. many modern engines have "dual path" inlet manifolds which change the air flow resonance depending on RPM....

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I massively need to do this. How long did it take you get the inlet manifold off?

Once the flexi ducts are off and pipes/tubes are disconnected, maybe 10 minutes. It's a bit fiddley, and you can't get the cover off without unbolting the trumpets.... (Not enough space at the back of the engine)

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You absolutely need those trumpets. They are there to set up a resonance or pulse wave to increase the air flow going into each cylinder. If you leave them off, you lose lots of power. The length of each trumpet is precisely tuned to give you peak power in conjunction with cam valve angles. short trumpets give you more power at high revs and no low end torque. long the opposite. somewhere in the middle is the best compromise for general driving. many modern engines have "dual path" inlet manifolds which change the air flow resonance depending on RPM....

Right, better put the buggers back on then :surprised:

Cheers

Ian

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  • 1 month later...

Update:

Went for a decent drive yesterday, first since doing the work over the last 6 weeks. I can honestly report that the difference in performance, economy, acceleration and overtaking ability is amazing compared to what it was like before (see pics above).

I'm not sure if it just the removal/modification of the EGR system (cat is still in place) or perhaps the limit adjustment of the throttle pedal. There is no smoke at hard throttle 3-4k revs and the engine just sings at motorway 'fast' cruising (I'm not going admit anything regarding exceeding legal speed limits on here...).

Economy returned just under 80MPG, with 2 cold starts, with mostly motorway driving. I brimmed the tank to the filler and then refilled out of a measuring jug to get the amount of fuel used, so I'd say fairly accurate.

The idle is smooth and quiet, with no nasty knocking sounds like before (with EGR active).

My only complaint is that I didn't want to use the cabin heater until I saw the temp guage hit normal, which took ages (and there's a new thermostat fitted).

I would recommend the corrective EGR action to everyone. My work comprised of the following:

1. Clean all the carbon deposits for the whole of the inlet system, right to the back of the inlet valves.

2. Machine up some aluminium plugs and block off the individual EGR ducts (4 of them).

3. With a die grinder, gas flow the EGR ports to allow a smooth airflow from the trumpet openings right to the cylinder head (I didn't modify the head at all- just cleaned it).

4. Smooth off any channels in the air induction tubes where they meet the manifold with high temp polyurethane goop, and smooth off with a wet finger.

5. Re-assemble entire cleaned air system to OEM (with EGR throttle valve still in place).

6. Reused old air filter as it looked new.

7. Block off oil mist inlet to plenum with a bicycle handlebar plug (perfect fit!)

8. Connect a 1m length of 20mm corrugated electrical flexi-conduit to the push-in elbow that sticks out of the valve cover, using a piece of glue lined black heatshrink tube.

9. Guide the 1m long flexi 'breather' tube out under the car so any vapours emerge unobtrusively below.

10. Lock anything loose down with cable ties. Job done.

Total time about 5 hours, but with many many tea breaks. :)

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