On 17 Dec 1997, dstauffa@csc.com wrote:
> After all, its not the PI per se that determines the hp, its the cam and
> compression ratio.
Not true. Not being choked by a venturi, and having essentially six
open pipes at WOT, the PI system has a significantly increased inlet area
(95 cm2 compared to 23 for a 150 CD, 31 for a 175 CD or even 51 for 3 DCOE
40s). This definitely has a significant impact on power output, given a
suitable cam profile.
> The PI can be
> calibrated to deliver a wide range of fuel to the cylinder. It would be
> easy to tone it down to meet US emission standards.
The Lucas PI fuel metering is based on two simple principles:
1. Proportional to RPM (goes without saying for injection systems).
2. Governed by engine vacuum, translated via a fuel curve (the
mechanism for which involves a couple of springs and a cam and
roller, with a number of adjustment points).
The problem with #2 is that engine vacuum is not a very good way of
determining air volume - the relationship between vacuum reading compared
to air pumped per stroke is not constant throughout the RPM range.
This simple approach is good enough if it is max power and good
driveability one is seeking, but probably not good enough to fulfill the
requirements for a de-smoged car.
See also:
http://home.sn.no/home/egilk/t_pi.html
Egil
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Email: egil@kvaleberg.no Voice: +47 22523641, 92022780 Fax: +47 22525899
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