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      11-04-2009, 03:38 PM   #1
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Arrow 335i Turbos - Stage 2 now installed and reviewed!!

Some of you will know that on the recent UK8 meet in the Lake District my car was giving a little bit of smoke out of the exhausts only when at a standstill. Under power the exhausts were clean with no smoke, although I had noticed that the engine was perhaps a little lacking in outright power (relatively speaking!) There was a bit of a smell too, sort of oil burning, but again only when the car was stationary

With all this in mind, and given the car has now done 40k miles of hard driving I thought it prudent to strip the engine down and examine the various parts, particularly the turbo bearings, seals, and wastegates. My car had been running fairly rich in terms of its fueling in order to protect the pistons from meltdown and I had a feeling that there was going to be a fair bit of carbon buildup

On initial inspection we noticed that the oil catch can was almost full, which was a bit of a concern as it's designed to prevent oil deposits from reentering the intake system and carbonising up the valves. The fact the catch can was so full meant that there had to be some oil passing back into the intake system and if there is oil in the intake system that will account for the smoke out of the back of the exhaust.

However the valves themselves were very clean and hadn't coked up and the rest of the intake system was largely oil free as well. This prompted us to examine the cyclonic oil filtration system in the cam cover but as it's a completely sealed (and stupid) design in one piece there's no way of telling whether the cyclones themselves are completely blocked without hacking the whole thing apart I decided to adopt a 'just-in-case' approach and changed the cam cover anyway, reassembled the engine and fired the car up. The result was the engine idled and ran much smoother with no hesitancy at all. But there was still some smoke once the car was warm, and still with the smell of burning oil.

Engine apart again, exhaust off, downpipes off, steering rack off, suspension moved out of the way - just to get the sodding turbos off the car!! Quite a ridiculous amount of work (thankfully I didn't do any of it!) to get the turbos out in the open to view.

In short, the turbos are in a bit of a sorry state! There is considerale carbon buildup along with oil seepage past the bearings and seals. The compressors look a bit worn, and the wastegates when in their fully 'closed' position still had daylight shining through the poppet valve. No wonder the engine was a bit lacking in power And no wonder there was smoke and burning oil!!

The turbos were shipped down to Turbo Dynamics ( in Dorset a few days ago for inspection and to see what could be done to overhaul them, or even upgrade them to perform better. Turbo Dynamics are one of the world-leaders in turbo development, building, upgrading and fettling. The reputation is phenomenal, and if anyone can work some magic on these crappy Mitsubishi turbos that are used on the 335i, they can!

The bottom line is that the turbos can be overhauled, but they would probably wear themselves down again in similar fashion as the turbos are running close to the edge in terms of the performance they can deliver in their factory state. The better option is to get them overhauled and upgraded internally so that the flow rate is better and components used which are much longer-lasting with the resultant improvement in durability and performance. With suitable remapping by DMS I'll be able to achieve same amount of power from the engine I have now, but at a lower boost level with consequent reduction in turbo temperature and stress.

There's no point in changing the turbos, as there'll be fitment issues as well as the need to manufacture custom exhaust manifolds and all sorts. With the improvement in efficiency, durability and performance, there's no reason why I can't get over 500bhp from the engine if I wanted to. The main limitation will be the injectors and fuel pump. However my intention is not to go crazy on power - I'm very happy with how the car was performing anyway, so to be able to achieve the same but at far lower stress and heat levels is a major achievement

I had concerns that a larger compressor wheel and increased flow rate will result in an increase in turbo lag, but instead the way Turbo Dynamics develop the compressor wheel and how the compressor housing is enlarged will in all likelihood decrease the spool-up time of the compressor, so if anything the turbo might end up being more responsive than factory. Anyway, the proof will be in the driving, so I'll report back about that later.

I received an email back from their Technical Manager today with a bunch of pictures and information. I'll quote from his email -

The following pictures here show the end of the bearing housing that was leaking. You can see the carbon build up around the ring area and some corrosion starting to form on the surface.

Bearing housing before processing

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Bearing housings before, and after, processing

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Bearing housing after processing

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The after picture shows quite clearly how effective their cleaning and blasting process is with all carbon deposits and corrosion removed from the bearing housing before any machine work can take place to re-ring the bearing housing and open the recess to suit a larger compressor wheel.

The next lot of photos show the compressor cover and wheel before processing and getting ready for them to be machined. Nothing with any dirt or corrosion can go through the machine shop as any form of contamination could be detrimental to the process.

Compressor cover and old compressor wheel before processing

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Compressor covers before and after processing

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The next picture shows the carbonisation of the oil on the back of the heat shield compared to one that has been cleaned and blasted.

Heat shields before and after processing

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The next picture shows the shaft and wheel. You can see the heat soak suffered on the shaft by the discolouration and the carbon build up around the ring area.

Shaft before and after processing

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The next load of pictures show the turbine housings and manifolds before and after processing.

Turbine housing before processing

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Turbine housings before and after processing

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Turbine housing after processing

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They did all this work in one day, and are continuing with the upgrades tomorrow. I'll have more pictures emailed over soon. Can't wait to get the 'new' turbos back on the car and get it running again in real anger! Will continue this thread when I have more info.