I suspect the chambers are virtually identical.. The Cosworth does get a
little timing hungry above 9800 though made some improvements running 38
degrees there but was pretty dicey. I save that setup for the return run
and not the qualifying one.. I look for egt around 1375 and air fuel
ratio where ever it likes it but typically 13.0 at 10k rpm and 13.5
around 8k the whole thing is on the wrong side of the curve above 9500
as far as efficiency goes but does pull 304 at 10.3k with the worst oil
pan I have ever seen but the only one that will fit the car. I suspect
there is another 20 hp in the pan yet to be had. It just won't fit the
car though.
The timing curve looks like 1k-1.8k 28(idle) 1.8-3k 34(slope) 3k-7k
34(flat) 7k-8.5 32(slope) 8.5k-9k 34(slope) 9k-the moon LOL about 11k 38
(flat) these are all in a slope that changes gradually between the
points. the reason for the timing out at about 8.5k is peak torque is
the and it needs less to make best torque.
Dahlgren
Tim Schoeny wrote:
>
> 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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