Toymods Car Club Inc: Tech & Conversions => ATDC (After top dead centre ) ??? Pls xplain ?

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RWDboy
Forums Junkie

Location:
South Australia
Registered:
July 2002

Re: ATDC (After top dead centre ) ??? Pls xplain ?

Thu, 29 May 2003 16:02

You'll find that the distributor has a counterweight set-up hidden away that operates on centripetal (or is it centrifugal, can never remember) force that generates advance as the revs increase.

Robert Bosch wrote a good reference book on fuel & ignition systems, but I can't remember it's name, will look it up next time I go to uni. Unfortunately, to say that having ATDC improves emissions in general is a bit of a fallacy. See generally with lower nitric emissions, you will get greater carbon monoxide emissions...it's one of those equillibrium/catalytic systems, you shift something one way then the other goes the opposite.

I think it's to do with available oxygen being spent one way or the other. Would look it up, but year 12 chemistry is a distant memory that I don't want to re-live!!!
I leave my road ignition settings to the engineers, and my race settings up to the dyno

Ignition advance does generally equate to greater power/torque due to there being more time to burn, and also the fuel gets burnt during a period of higher compression. There are of course, hazards to ignition advance, and it varies alot with different modes of operation (over-run as Bosch calls it, full throttle, temperature of the intake charge etc can also be factors). Quality of fuel is also important.

Quote:

If you have an old car with slightly low compression, you don't go and put ultimate fuel in it!

I'm not sure I'd believe that (but I'm not a know-it-all), fast burning fuel will require ignition timing that is more retarded (not in a spastic sense), whereas a slower burning fuel (higher RON) will be able to advance the ignition over standard, giving better torqure down low, and at least equivalent upper-rev range performance as well.

I think having faster burning fuel has some heating issues as well, but I'd have to find that book to confirm that. More energy gets converted to heat rather than kinetic energy maybe? Not sure. Also if there is an issue with heat, that can change the equillibrium in the whole emissions equation. It's a way too complex an issue to remember everything, maybe I'll get that book and hit this post again

(In a way I'm admitting I'm not an ultra-reliable guru on this subject).

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