Manifold vaccuum, EGR & long duration cams

[Fred Miranda]

Tony,
I think you would be better off going with a table. Fill it with #s that 
work through trial and error and forget the airflow calculation.

You've probably got pulsations on the plenum. So you need to either
filter them out or time your map readings to the crank, or the system will 
go nuts.

Since the engine idled on the other system, it will obviously idle on
this one if it is fed the same fuel and timing.

Fred

At 05:21 PM 1/31/97 +1200, you wrote:
>In an attempt to go from my very bad RPM/TPS system 
>to a reasonable MAP system, I built myself an conventional
>arrangement plenum chamber, and tossed the
>DCOEs I was using as throttle bodies.
>
>However, It doesn't idle at all well.
>
>Setup: 72 degree overlap cam, largish plenum chamber, MAP system
>
>Problems:   
>  Won't idle below 1500 rpm. Simply dies if revs drop below 
>  that. Starts easily though. No idea how well it goes under
>  load at higher rpms.
>  
>  (used to idle at 500rpm on tps system or carbs)
>
>  At 1500 rpm with spark advanced for maximum
>  vaccuum (13" Hg), actual fuel requirement 
>  (as determined by using a colortune windowed 
>  spark plug) is 1/4 what it should be, according 
>  to the MAP calculations.
>
>Hypothesis:
>  During overlap a large amount of exhaust gas is being
>  sucked back into the cylinder & plenum chamber, effectively
>  giving me the EGR system from hell. 
>
>How to fix?
>
>I've so far managed to stay away from 2D tables, and stuck to 
>parameterised formulas. (For ease of tuning).
>
>Do map systems generally cope well with high overlap?
>
>Will I have to retard the ignition at idle to slow it down 
>below 1500?
>
>thanks...
>
>
>
>
>$$$ MAKE CAR FAST $$$
>bryantt at psc.fp.co.nz
>
>