James517

100LL - is 100 octane, leaded fuel available at many airports.

The engine was a 1.8L, air cooled (essentially), Type 1 (bug) VW engine with approx. 8.1 compression.

Tried ethanol free, unleaded premium (about 93 octane). Got noticeable soot from the fuel. Although I didn't like the way the engine ran, others who use it have noted more soot than the older style leaded fuel. The leaded fuel also seems to be more stable and can be stored longer without additives.

The flip side is, that for some engines, the leaded fuel creates deposits that have their own issues for rings/valves/tappets.

No free rides.

Dshady

Catalytic converters do not like even low lead fuels. Could the soot be due to direct injection? Is the gas A6 direct injection, TDI guy so not sure.

DB22

Good question, again it would add more context to the conversation if people's location was embedded in their posts.

SGMJohn

ScrewGuy

Thanks for the tip on the Simichrome Metal Polish. I ordered some from Amazon and when it came in, WOW! Sure did the trick! Just for grins I looked at the cost of tailpipe extensions, blew me away with MSRP of $350 each! I'll stick with the Simichrome Metal Polish.

Fahrer

DI engines produce soot for reasons similar to diesels. The fuel droplets do mix with air before entering the combustion chamber and some of the fuel droplets hit the piston before vaporizing. There is less time for the fuel to be absorbed/mixed with the air. This forms more soot.

DB22

I am not convinced.
Today's engines have much cleaner combustion than the older cars and they try to get a perfect swirl before ignition to eliminate the pollutants. Additional soot would clog cats in no time, would fail pollution limits, be less efficient and increase fuel use.
DI is only possible today because of todays faster computers. DI in the old days was dump approximately the correct amount of fuel then add a bit more because what you don't use will be thrown out of the tail pipe. Those days are over.
Carbon build up has been an issue with DI however but most of that inefficiency is due to the engine not being up to temperature.

Fahrer

Actually, engines ( including VW and Audi) for the European market are now being offered more and more with both DI and port injection. The DI injectors are only used for idling and for full power. The port injectors are used all other( ~80%) times to reduce pollution. Port injectors result in much better ( air) mixing and reduces soot. The only advantage DI offers is improved cylinder cooling so the compression ratio can be increased, yielding a bit better mpg and power but at the cost of increased pollution. The port injectors are not normally offered for the US market as the particulate standards are not yet that strict and for cost savings.

Check out the attached ( slide 23 for EU and slide 25 for the US market)

http://www.cargroup.org/assets/speak...idt_oliver.pdf

DB22

It's getting very complicated. The good old days when Cadillac wanted to increase torque they just increased the engine size until they got up to 500 ci and then realized that there must be a better way! Now the challenges of pollution and MPG's are exponentially advancing. I see 3 cylinder/hybrids of 350 HP in our future?

Fahrer

Could be ... could be. For sure though, the engines keep getting smaller and the hp keeps going up but with the aforementioned complexity.

DavidA

A8 uses 93 octane, causes some soot, got rid of the black stuff w/ Terminator from 'Stoner' (same brand as Invisible Glass)
it may be hard to find or use WD 40 with a paper towel. It has worked fine for the chrome w/ soot. You can use steel wool "0000" extra fine also but only if its stubborn...