What kind of EGT's are you looking for in trying to determine optimal timing or
are
you using other criteria?The Honda seems to like about 32-34 degrees total
advance
above 6000 RPM and so far we haven't burnt anything up.It's interesting you
mentioned
32 degrees for the Cosworth which I assume has a pent roof chamber similar to
the
Honda.Any thoughts would be appreciated.
Tim Schoeny
dahlgren wrote:
> I was referring to peak pressure as opposed to the burn being done. two
> different #'s. And yes advancing slowly until peak power is the best
> bet. On the dyno I usually start with something that sounds realistic
> and the retard the timing 2 or 3 degrees and if that is a loss in power
> i go for plus 2 to see if it wants more advance. I always go for the
> safe test first and have been pleasantly surprised on many occasions
> when the power went up taking a couple of degrees out. At Bonneville you
> have two reasons to change the timing. The first is the density altitude
> which says you might want to advance it and then the air temp that says
> you might want to retard it..Comes out as a wash on lots of occasions in
> my experience.
> Dahlgren
> Dahlgren
>
> "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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