""I found my
problem when I got home"", Tom, can or do you desire to share, I am most
interested, if you would rather not lt us in, understood, I will share some
"learning experiences" as well, not always easy to do, depending on the find.
Joe :) :)
Thomas E. Bryant wrote:
> Excellent dissertation on timing. However, it seems that there is
> disagreement as to when the burn needs to be completed, I had read 23
> degrees ATDC, in an other publication 20 degrees ATDC, now you give a
> different number, which I don't dispute. It is just that as a layman,
> the way I find what works is to keep advancing the timing carefully
> until it doesn't improve performance anymore and then back it up a
> couple and lock it down.
> Several years ago I went to a Champion Spark Plug Seminar where they ran
> an engine equipped with thermal coupler spark plugs on a dyno. To show
> the effects of advancing timing beyond specs, they ran the engine
> measuring HP and cylinder temp at increasingly advanced timing setting.
> It was interesting how HP increased up until 4 degrees over advance
> while temp increase was minimal At 6 degrees the HP increased a bit but
> temp climb substantially, past this there was a rapid climb in temp with
> little or no HP increase. This was a stock Chevrolet engine, but I am
> sure that the physics would be similar with the race motor.
>
> I am aware that cylinder heads have much to do with needed timing. That
> is why I was concerned about the timing I was putting into my motor at
> Speedweek. I had to do this years ago, but the heads I am running now
> are suppose to be superior to those I ran in the yesteryear. I found my
> problem when I got home, but I suppose a wiser tuner would have
> investigated further at the Salt. I was just having too much fun!
>
> Tom, Redding CA - #216 D/GCC
>
> dahlgren wrote:
> >
> > I am very sure that the amount of ignition advance you run tells you a
> > very important thing about your engine, well two actually. The first and
> > most important thing that I have learned is that there is a direct
> > relationship between the amount of the ignition advance and the design
> > of the combustion chamber. This is a very important thing to anyone
> > racing. The better the chamber the more power that can be extracted from
> > the fuel, the engine becomes more efficient. You have pointed out a
> > very good example with the 50 degree timing and the shrouded plug. If
> > you unshrouded the plug on that engine and did nothing else other than
> > reset the timing you would of made more power. The reason for this is
> > pretty simple. When you fire the plug that early and start the fuel
> > burning more of the energy goes into the surrounding metal as waste heat
> > rather than push the piston down. The ideal time for peak pressure as I
> > have understood it is right around 15 to 17 degrees after TDC. With that
> > said the most efficient time to burn the fuel is about 15 to 17 degrees
> > ATC so that all the energy goes into pushing the piston down and less
> > goes into the cooling system. The only problem with that is it takes a
> > certain amount of time for the spark to occur and the flame front to
> > propagate. This time is compensated for by ignition timing advance
> > expressed in degrees as it is the easiest unit to measure. If you look
> > at the timing as microseconds of delay time instead of degrees a very
> > interesting thing happens. First thing it does is take rpm out of the
> > picture and explains why you have to add more timing as engine speed
> > goes up. It also gives you a very nice number to show the relative
> > efficiency of the chamber. Different cylinder heads have delay
> > time/advance curves that are very common to them. ex, SBC 23 degree
> > about 38 degrees, Cosworth DOHC 32 , Ford Yates style head 34 and so
> > on.. what you want to do is work on the head chamber plug combination so
> > that the ignition timing is the smallest number that will burn the fuel
> > completely. The other important point is the faster the burn time in the
> > chamber design the less likely you will any preignition/detonation as
> > there is less time for a second flame front to develop in the first
> > place. So when I hear that someone is running a lot of timing to get
> > peak power I see a bomb waiting to go off and also an engine that is in
> > real need of further development. The timing is a crutch for a problem
> > in engine design, a lot of which can be avoided by proper chamber design
> > and spark plug placement and shrouding.
> > When the tuner becomes expert and sees big timing numbers a bell should
> > go off in their head and tell them to pull the heads and find the real
> > problem they are covering up with ignition advance and not write it off
> > to a tuning thing. Every time you change the timing or jetting or fuel
> > mixture/burn time in any way there is something to be learned. the
> > engine is telling you all about how it is doing and how good the overall
> > design is, but you have to listen to it too.
> > Hope I did not bore anyone with this but my 2 cents worth..
> > Dahlgren
> >
> > Marge and/or Dave Thomssen wrote:
> > >
> > > On spark advance from an old-timer.
> > >
> > > Correct spark advance is a matter of experience and experimenting. Every
> > > engine set up differently will need different advance. Some setups are so
> > > similar that they take the same advance. When I used to run my 8:1 ARDUN
> > > with the plugs somewhat recessed I set it at 52 degrees(!) with 10 pounds
>of
> > > boost or unblown. I worked up to that number gradually. Now that this
>one
> > > is 9:1 with better quench 42 degrees seems good blown and unblown. My
>12:1
> > > ARDUN with unshrouded plugs likes 36 degrees. My flatheads like 28
>degrees
> > > when there is a lot of clearance between head and piston. If the
>clearance
> > > is tight or the blower in attached they like 22 degrees. Some guys run
> > > flatheads at 10 degrees. The engine tuner becomes the expert on spark
> > > advance with experience.
> > >
> > > Dave Thomssen
> > > #322 XXFSTR
> > > The Hayseed
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