fast times in the hammertown

[type53b_gtd]

The question is not how much soot the car blows, but at what rpm does the car blow soot?

If it's blowing soot through the entire rpm range, then it is overfueled for the air charge at the given rpm and boost level.

However, soot at high rpms (approaching or exceeding stock goverened speed) implies that the amount of fuel injected cannot be burned within the combustion window - which in terms of degrees of crankshaft rotation is the same size, however in terms of real time, occurs in half the time at 6000 rpm as it does at 3000 rpm.  At this point soot will occur regardless of intake charge - even with a boost pressure of 60 psi the engine will smoke, because the fuel doesn't have enough time to burn completely before it is expelled via the exhaust valves.

Running fuel with a higher cetane level decreases smoke because the fuel will ignite earlier in the compression stroke, meaning more of it will be burnt. - I believe I read Dr Diesel has shaved pintles as well to advance the start of injection?

Although the concept of the (really) high speed diesel  seems to me to be wasteful, and in the long term, detrimental to the engine (and the environment... )  It's still pretty damned cool though, having said that, and I would love to see it in action.

Drew

[Dr. Diesel]

I'm constantly making changes to the settings on my pump and boost. Literally, it's never the same one week to the next. I find even weather changes make significant differences in how my engine runs. Usually, I have the old hunny set to an economical, clean burn. For racing, I have found a little smoke under full boost isn't quite as powerful as a lot of smoke, and certainly, with such overfueling, turbolag is significantly reduced, much to the chagrin of bystanders or behind-drivers.
Bottom line is, without additional complicated mechanisms, a mechanical pump is always going to be a compromise between power and emissions.

[type53b_gtd]

Agreed on all counts.  This past winter I had a blast with the Scirocco, as it could handle very agressive fuelling with relatively little smoke.  I'm still trying to find the compromise now that the warmer weather has arrived.  On a recent caravan with a number of other Scirocco owners I was branded the mosquito repellent...

Last night I swapped out my A1 airbox for a slightly modified A2 airbox, which did make a noticeable improvement in off-boost and low-boost performance, but I'm having trouble coming up with an LDA cone setting that has sufficient fuelling above 6 psi and doesn't smoke like a pig below 6 psi.  In the end, I may surrender unplumb my intercooler for now, as I just don't spend enough time on boost above 6 psi to make it worth while.

Drew

[Turbo DS]

A lot of what you guys are describing regarding engine tune, sounds a lot like intercooler heatsoak effecting the charge, and simply warmer, less dense ambient air.  

When its cold or cool the fmic in my car is adequate (thermally, but mass flow wise its crap).  However, when the temps get over the 60s, the fmic will heatsoak too quickly.  Granted, there is still more than enough power, but I know far more power is being wasted to heat.

A *real* fmic is on its way... :twisted: