Some of you who know me personally know that I am an inquisitive fellow by nature. At the age of six my first bicycle lasted all of three hours before it was completely disassembled. Probably drove my parent nuts with "how" and "why" questions as well. Luckily, they chose to let me live.

Anyway, two questions have bothered me since moving from the Gen 1 platform to the Gen 2.

1. Why all the soot in the tailpipe?
2. Why is chain stretch such a problem?

Initially I made assumptions like "Well Mini's burn oil so it must be because of that." and "BMW must not have used pre-stretched chain material or the load with the vacuum pump and HPFP is just too much for the chain."

Recently however I came across a study that I think sheds some light on both of these questions. I think it also helps illustrate the automotive industries tendency to sometime leap before looking at long term implications.

For those that do not wish to read the entire study I'll give you the cliff notes version before posting the link below. Some of this may seem counter intuitive to all the hype from the auto industry about direct injection. Just keep in mind that with traditional port injection the injectors can be open for nearly the full 720 degrees of rotation whereas GDI injectors must perform their function within a maximum of 310 degrees of crankshaft rotation.

1. Direct Injection results in a less homogeneous gas-phase mixing resulting in incomplete burning and clumping of particulates. In fact gasoline direct injection engines produce more soot than diesel engines equipped with a particulate filter.

2. These soot particles invariably build up in the engine oil and increase the rate of wear. In point of fact chain "stretch" is considerably accelerated by elongation caused by wear of the chain pins and bushings.

So know we now the how and why of a great many of the reliability problems these vehicles suffer from. So what's next? I think we can infer some solutions to help us happily motor on much longer.

1. Change your oil more frequently. Yes, synthetic motor oil will in fact retain it's viscosity and lubrication properties much longer than conventional motor oil even up to six or eight thousand miles. But no matter how good the oil is it's not able to do it's job very well with a handful of sand thrown into it. As soot accumulates in the oil it will increase the rate of wear on the timing chain, turbo bearings, main bearings, etc...

2. Consider increasing your oil viscosity. Oil film thickness correlates to viscosity when measured in a kinematic or high shear rate viscometer. A thicker oil film will do a better job of preventing larger particles from abrading surfaces. Manufacturer's are constantly pursuing increased gas mileage and efficiency and many have lowered their recommend oil viscosity to further that goal. My wife's Subaru (gasp) has a recommended oil weight of 0W-20

3. There's been some question as to if or why cryogenic treatment of the timing chain by some of our vendors (Detroit Tuned) results in less chain stretch. The short answer is that cyro treatment increases hardness and abrasion resistance. The conversion of austenite to martensite results in an increase of about 2 on the Rockwell hardness scale and the precipitation of Eta-carbides helps close the grain structure of the surface of the metal. Both combined will result in a longer lasting chain.

Here's the full article for those interested.
http://www.sciencedirect.com/science...01679X15000432

Food for thought.

 

And all this time I thought the increased exhaust soot was from my "spirited" driving...

Seriously though, I love analysis like this. Great writeup with specific explanations/examples.
I definitely noticed less oil burn/soot when I switched to a higher viscosity oil (5w-40)
Thanks Tigger

 

Thanks for the write up.

 

You also need to remember that DI combined with the heat of turbocharging and the use of a timing chain results in high amounts of oil shear. All of these combined factors reduce the lubricating properties of the oil at a quicker rate, which ultimately results in a higher rate of wear for the timing chain.

Plus, throw a little oil dilution and oil consumption in there (natural with DI/Turbocharged engines) and it's the perfect recipe for issues.

My solution is to change the oil every 5k with the most shear-resistant approved oil you can find. Cheap insurance.

 

So how do you determine an oil's resistance to oil shear?

 

You're welcome sir. I noted the same as regards to oil consumption with 5W-40. When running a Stage 2 meth tune I changed oil at 4000 mile intervals but since switching to pure meth, installing the 51mm turbo and upping the boost to 1.7 bar I have shortened it to 3000 miles.

 

I figured that the soot in the tailpipe was due to an enriched fuel/air ratio at startup.

 

Good idea on reducing the oil change interval with that level of boost.
Im jealous...Vlad was an absolute beast on the Manic Stage 2+ with meth, I can only imagine it now with a 51mm...

 

This explains it far better than I ever could: https://www.bobistheoilguy.com/oilshear.htm

 

Well the turbo is still under ECU control and on the Stage 3 tune we pulled a fair amount of timing to keep it safe, but at 291whp Vlad is indeed a bit more frisky these days. I'm also glad I installed the Wavetrac LSD. It seems to be doing a really good job of keeping the wear even on both front tires.