Joe when I checked my actual Valve to Piston I did it Ten Before and ten
after... Just to make sure I was Okay to alter the Degrees on the Cam if
nessesary.... I did this AFTER we ran it on a Dyno... which is Major League
Stupid.... because we had already changed the Cam Timing on the Dyno....
Now I know better... when my engine guy actually got an understanding of
what I wanted to do with the Belt Drive He came to the House and we checked
it all out... this of course we a direct result of Dave's Question about
Actual Valve to Piston Clearence...with different Rocker Ratio's
It's a Number you Simply have to know up front... again I am storing all
this information so I can come back Later and Maybe fix some of these
Mistakes...
Keith ( why Yes.... I am Learning.... Just SLOWLY )
----- Original Message -----
From: "Joe Amo" <jkamo@rapidnet.com>
To: <saltracer@awwwsome.com>
Cc: "dahlgren" <dahlgren@uconect.net>; "Marge and/or Dave Thomssen"
<mdthom@radiks.net>; "Land-speed Racers" <land-speed@autox.team.net>
Sent: Saturday, August 26, 2000 2:05 PM
Subject: Re: Timing advance
> Tom, so bare with me here as many of us bike guys have DOHC, we degree
cams in using
> lobe centerlines, do you not set the cam timing using lobe centerlines?
It sounds like
> you use actual degree numbers of opening and closing is this correct?? If
you use
> centerlines, the centerline stays consistent no matter if checking at
0.20" or at
> 0.050", do you then check valve to piston at say from 10 degrees before to
10 degrees
> after TDC? It would seem that checking 10 before to 10 after would show
the valve to
> piston discrepancy no matter the method used to set the cams. Please
enlighten me. Joe
> :)
>
> Thomas E. Bryant wrote:
>
> > Joe,
> > I had published it already on the list, but here goes again...The last
> > run we made on Thursday we advance the timing 1 more degree, (our
> > fastest run, 222+ MPH, was with 49 degrees BTDC). We also leaned the
> > mixture .002 which was a mistake. The engine detonated before Jeff
> > shifted out of low gear, he went on through the three mile and shut
> > down. We lost #4 & 6 spark plug electrodes and dusted # 6 piston near
> > the spark plug. Luckily, no major damage. I found that all the intake
> > valves had been colliding with the pistons and with deeper analysis,
> > found that I had degreed the cam incorrectly.
> >
> > The cam card gives two numbers that got me confused. The timing spec is
> > .020" of valve opening, the duration is checked at .050" valve opening.
> > I obviously set the cam timing with .050" of valve opening, which when
> > rechecked at .020" read 69 degrees BTDC rather than the spec of 53
> > degrees. After resetting the cam timing, I had more than .100" of
> > clearance between the valve and piston. This was a major mistake. I had
> > set it up correctly when I was checking valve to piston clearance in the
> > beginning, I don't really have an excuse for setting the cam timing at
> > .050. Just brain fade I guess, but I don't think that I will do that
> > again. I try to learn from my mistakes.
> >
> > Tom, Redding CA - #216 D/GCC
> >
> > Joe Amo wrote:
> > >
> > > ""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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