does any mod...

[Konstatntin Bogach]

Thanks for such comprehensive answer. 
Does it mean that RZ/stiffer_spring mod will not suffice to drive at
1.8-2.0 bar because of lacking of additional timing entries?

Ameer Antar wrote:
> 
> this is a loaded question! well, first a look at CIS will help. The A/F
> ratio is not calculated by the ECU. In fact, the air-flow sensor is what
> determines the A/F ratio for the most part. The higher the air-flow plate
> is, the more fuel is allowed to enter the injectors. The angle of the cone
> around the sensor plate dictates how the plate moves for a given amount of
> air. This cone is calibrated for a stoich 14.7:1 A/F ratio. The more air
> flows, the more fuel...all this is so the A/F ratio remains the same.
> 
> Now the ECU takes info from the O2 sensor and adjusts the mixture really
> thru the air-flow sensor plate. This is done by the CIS freq. valve
> adjusting the fuel pressure which sits on the plunger which is attached to
> the air-flow sensor plate. This adjustment of pressure atop the plunger
> adjusts how easily the air-flow sensor plate is able to move. If you take
> off the air-flow sensor intake boot, you can feel pressure behind the
> plate, so that there is more resistance to air flow. Otherwise, too much
> fuel would be metered to the injectors. So the ECU really doesn't decide
> the actual A/F ratio, it only has a small adjustment to center it around
> whatever is metered by the air-flow through the sensor. So the ECU will not
> limit the movement of the air-flow sensor plate beyond 1.4 bar, it will
> continue to compare to the o2 sensor readings and shoot for the stoich A/F
> ratio.  The only real limit is the limit of air-flow sensor plate. Once it
> reaches its maximum level, the fuel dist. can no longer provide any more
> fuel and the A/F ratio will steadily increase as more and more air enters
> the engine. But it's been said that stock CIS can handle up to 2.0 bar.
> 
> In a modified vehicle, at 1.4 or 1.6 bar the A/F ratio should still shoot
> for the stoich 14.7:1 ratio. The WOT switch allows for a richer mixture not
> b/c the engine needs it to survive, but to give the car the max. amount of
> oomph at extreme conditions. If you look at a graph of A/F raitios, the
> max. power in an engine is a bit above 14.7:1, while max. economy is a bit
> below 14.7. Stoich is a compromise between those two conditions, and WOT is
> the only time you want the max. power, w/ disregard for economy. It's OK to
> use stoich A/F ratio at 1.6 bar b/c the engine will be fine...no need to
> increase D.C. But beyond that you begin to run into the problem that the
> engine is now running under very high compression, esp. at high boost. High
> compression is a problem b/c it maximizes the amount of energy released
> from combustion, causing excess heat and therefore pinging. The pinging is
> not caused by the wrong A/F ratio, but high compression. To combat this,
> what many tuners do is make the mixture richer to cool the combustion. They
> also use water injection to cool it. Another method is lowering normally
> aspirated compression [by changing pistons or thicker head gaskets] and
> using big intercoolers to lower air temps. But this is only a concern for
> very high boost.
> 
> A chip should do:
> -shift 1.6 bar fuel cutoff to some max. value [1.8-2.0 bar]
> -add additional timing entries for higher boost
> -adjust WOT boost value to some max. level [1.6-1.9 bar]
> -adjust any entries where timing is fully retarded beyond stock boost level
> 
> other than that, air-flow sensor plate will adjust the mixture
> appropriately as long as boost is kept within limits.
> 
> -ameer
> 
> At 01:21 PM 12/4/2000 , you wrote:
> >modify A/F ratio (thru duty cycle, I think it is the only way) at high
> >boost?
> >Do those chips do anything except changing cutt-off pressure value and
> >boost map?
> >
> >Thanks.
> >
> >Konstantin Bogach.
> >200tq 89