Opinions wanted ( analysis of the effects of spark advance variation on vacuum)

[Len Sabatine]

At 11:17 AM 9/21/2000 -0400, you wrote:
>Opinions wanted ( analysis of the effects of spark advance variation on
>vacuum)
>Did you disable the IAC, set the VE table so that for a given amount of
>timing the fuel baseline was the same?.
>Over what period of time was all this done?.
>How long was the engine run for temps to stabilize.
>Looking at the BLs, seems like the pcm was affecting the outcomes, by being
>closed loop.
>
>I'd suggest repeating things with the above considerations.
>Nice to see someone putting in the effort to really tune something and share
>the results.
>
>I've found that making cruise corrections takes the ecm 15-20 mins for each
>correction to really take effect.
>
    ^ ^ ^ ^ This is an area very much "Overlooked " and _Very Important.
    Really can't be stressed enough + heat energy recovered during _each
    combustion Cycle or the lack of. This is a BIG Deal.  v v v v v v.  > LS.


>While timing is a big concern, remember it's really about recovering heat
>energy.  ie having the optimum timing of when the reaction will be pushing
>the piston back down.  So plug gap will have a rather large effect also (in
>response to you using a .040" plug gap).
>Bruce
>
>
>
>
>
>
>
>----- Original Message -----
>From: cmillard at crutchfield.com
>To: gmecm at diy-efi.org
>Cc: Chipsbyal at aol.com ; ewright at silverback.gorilla.net ;
>douglas.t.wood at lmco.com ; jll at edge.net
>Sent: Friday, September 21, 2001 10:04 AM
>Subject: Opinions wanted ( analysis of the effects of spark advance
>variation on vacuum)
>
>
>Friends, Programmers, Hacks, Lurkers-
>.
>I would like your feedback/ opinions on a little experiment I did.
>The experiment was studying the effects of spark advance (closed throttle)
>on idle vacuum.
>.
>Please take a look at it here:
>http://cmillard.freeservers.com/Z28/PCM/Ignition/idle%20spark%20tuning.htm
>.
>My theory was based on for the same given RPM (900 rpm) the spark advance
>which yielded the highest vacuum would give the best fuel economy. The MAP
>sensor reads opposite vacuum (higher vacuum is lower MAP, and vise versa),
>so I was shooting for minimum MAP. I plan to apply this to idle at first,
>then the entire timing map, if enough data can be collected.
>.
>This is based on Bruce's tuning tips I read about two years ago on ECMGuy's
>page, which just started to click in my short circuited brain (zap!)
>.
>The test vehicle uses a '8051 (as Daawagon and Dave H. called it). The
>16188051 is factory in my 1995 Camaro Z28 running 11.4:1 compression with a
>LT4 HotCam (219/228 .525/.525 112)
>.
>I did several excel pivot table charts based on data from about 12 flashes
>with closed throttle spark advance varying between 12 and 34 degrees. Here's
>what I found:
>.
>The higher the spark advance the higher the vacuum ( to a point, up to 36
>degrees advance ) Optimum spark at idle was 34 degrees, factory was 20
>degrees- whoa.
>.
>The higher the spark advance the lower the injector pulsewidths (matchs
>vacuum), again to a point. This again would help to suggest better gas
>mileage.
>.
>Sorry for the rant, it's Friday.
>.
>Your feedback is appreciated,
>-Christian
>(disclaimer: working on 2 hours sleep)
>http://cmillard.freeservers.com
>(Feel free to snarf the folders of my site for amusement)
>Christian Millard
>Application Developer
>Crutchfield Corp
>www.crutchfield.com
>
>
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