RE: alfa-digest V7 #1156 Spica "Improvements"

[bearbvd@domain.elided (Greg Hermann)]

>> I would appreciate receiving detailed definitions and descriptions with
>> documentation of these "improvements" from anyone involved so I can pass
>> them along to Dario Radaelli (the developer of the system) for his
>> comments.
>
>i'll try.
>
>for the non-ingram mods, i know of two.  the first was done by ven fonte,
>although i don't know if he thought it up himself or was told by others.
>basically it involved stretching or replacing with a looser one) the spring
>in the section of the pump that holds the centrifugal ball.  the idea is to
>allow the ball to increase its orbit faster, which slides the 3d cam
>sideways (or lengthwise) faster, which pumps more fuel faster...
>

>the street pump is 'simply' a rebuild, to much tighter tolerances than
>original, of a stock pump.
>
>the high performance pump is the street pump with a modified cam.  wes does
>not recommend this pump for a street motor, the motor has to be fairly
>heavily modified to take advantage of the high performance pump.
>
>for the record, *my* rendition of the ultimate gtv ('71 of course) has a
>stock 1750, balanced, with euro cams, very mild porting (just a clean up),
>and an ingram street pump.

Rebuilding what is essentially a diesel fuel injection pump to tighter
tolerances seems to me a plausible proposition. This is pretty common
technology.

However--I would have to say that re-profiling the alpha-n fuel cam to suit
a different engine set-up would be a _HIGHLY _ finicky operation. Best one
could really hope for would be to be somewhat too rich--and in varying
amounts-- throughout the power band. I can recall working with a stock 1750
GTV, new. Something as minor as setting the valve lash to .016/.018 (rather
than the stock .018/.020) would leave one with a slight flat spot when
mashing the throttle at about 2000 rpm!! Any Alpha-N fuel curve is simply a
_VERY _ sensitive beast.

The idea of using one "high-performance" profiled cam to cover a multitude
of possible engine tuning situations therefore seems to be pretty
incredible to me!

Other side of this is that a mechanical injection pump has some wonderful
characteristics of which electro-magnetic injectors are NOT posessed.
Mostly having to do with far greater dynamic range--being able to inject
all of the fuel into the port during high velocity air flow in the port,
even at full power.

Far superior fuel atomization is the other thing which comes immediately to
mind.

And--if you want still better fuel atomization than stock, try setting the
injector opening pressure up a bunch higher!

Another thing to pay serious attention to-- in order to equalize fuel
delivery to the cylinders--is having equal length high pressure fuel tubes!
Especially if you are tweaking the injector opening pressure, the
deflection of the tubes AND the compressibility of the fuel are BOTH very
significant factors.

OK--higher pressure, better atomization. Equalized fuel flow. Goth go
directly to better performance. Great! What to do about the metering
problem??

How bout using (easily available) a linear actuator (with position
feedback, preferably) to position the rack in the Spica pump--and
controlling said actuator with a modern ecu brain, with all of the usual
inputs--MAP, engine speed, MAT, throttle position, coolant temp, altitude,
etc. to set the proper fuel delivery for any given set of engine operating
conditions. If one combined this approach with feedback from a quality wide
band O2 sensor AND an EGT probe (or probes), I think one might well have a
system which would be easily capable of seriously outperforming a system
using electromagnetic injectors!!!

Regards, Greg

------------------------------