RE: [DMCForum] Turbo Bosch X-Jet?

["Dave Stragand" <dave.stragand@xxxxxxxxxxxxxxx>]

Thanks for the great explanation, Martin.
 
That actually brings me to a strange idea I had yesterday about installing a
second, 'boost' CPR that would get movement of the metering piston
mechanically based on manifold pressure, but not vacuum.  Probably possible,
but it would be difficult to implement.
 
The electronic FI makes more sense from a calibration standpoint, but I'd
like to get blood from the stone mechanically rather than electronically
when at all possible.
 
The Porsche & Lotus turbos that used Bosch CIS must have had some way to
effectively manage the turbo fuel requirements under boost, correct?  To not
reinvent the wheel, that's what I'm currently investigating grafting into
place.
 
-Dave

-----Original Message-----
From: Martin Gutkowski [mailto:martin@xxxxxxxxxxxxxx] 
Sent: Saturday, January 15, 2005 12:03 PM
To: DMCForum@xxxxxxxxxxxxxxx
Subject: Re: [DMCForum] Turbo Bosch X-Jet?


They work through the control pressure regulator lowering the control 
pressure proportionally to intake manifold pressure - much the same way 
as they do anyway but ours have a "ceiling" of 1bar (atmosphere). That 
said, you can fool the stock 066 cpr into fuelling under boost, but my 
experience is it does it rather too well...

The snag for you is that they also work for a proper turbo engine where 
the air is forced through the throttles, unlike the Island setup. The 
theory is sound in that the island setup uses the K-jet metering unit as 
a MAF sensor. Unfortunately the heisenberg uncertainty applies here (ok 
not quite) in that the action of observing/measuring the air flowing 
into the intake has the effect of changing it. New MAF sensors are not 
at all restrictive whereas the k-jet system is and therefore leans out 
proportionally with RPM but which can be compensated for by steepening 
the fuelling curve. Unfortunately a turbo engine hasn't got a linear 
fuelling curve, so they use the control pressure to dynamically adjust 
the mixture. The snag here being it must be properly calibrated to the 
engine in question.

Martin



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