David is right,
Probst book is an excellent primer on CIS and a "must" reading for anyone who owns Bosch injected car.
Another book worth reading is "How to Tune and Modify Bosch Fuel Injection" by Ben Watson. This book has more practical, "hands-on" approach. Both are highly recommended. Additional online reading about CIS tuning:
VWVortex.com - CIS, CIS-Lambda, CIS-E and CIS-EM FAQ and Tuning Guides
Modifications described above (in post #127
) reach over and beyond the scope of these books and are based on empirical experimentation encountered on Pelicanparts, Rennlist, Turbobricks and couple other Forums. : http://forums.vwvortex.com/showthrea...-Tuning-Guides
David is right in saying, that you should not consider
replacing OE hydro-mechanical WUR with digital (DWUR) or boost sensing unit, unless
you're going to install larger turbo, increase boost or radically improve the air mass flow.
Bosch CIS system is quite flexible and able to adjust to some improvements in the air flow. Contrary to the popular belief, CIS system delivery is not limited by injectors (mechanical injectors have no duty cycle), but only by the fuel distributor.
CIS Esprit engine has a couple of choke points:
1. Turbo is intentionally "smaller" to provide snappy response and a minimum lag. Unfortunately, it creates a significant exhaust gases back pressure.
2. Turbo-to-down pipe adapter bore ID is smaller than the turbine port ID (!)
3. Mass Air Flow Meter is maxed out (only 108mm) to flow any significant additional amount of air.
Until you remove these performance obstacles you don’t need to replace the WUR
My point: If you introduce radical changes, you'll have to take care of the continuous enrichment under boost in order to avoid engine damage. Therefore,
the Control Pressure has to be modulated via continuous WUR adjustment in function of the rpm and MAP. Some Turbobricks forum prefer another method, i.e. grounding pin #11 ("accelerator pump" of the CIS ECU). [URL=https://www.lotustalk.com/forums/usertag.php?do=list&action=hash&hash=11].
It can be done either digitally, with an application of the UTCIS "PT" Digital WUR, (UnwiredTools UTCIS-PTâ„¢
) or mechanically by applying the IM plenum pressure signal to one side of the diaphragm in the WUR lower chamber. Boost sensing WURs were used on 1980-s Volvo turbo, Audi TQ, MB, Saab, Porsche, BMW, etc., but mysteriously Esprit was outfitted with bare-bone N/A-type
CIS system (another example of a cost avoidance).
FYI: some folks made about 345hp with 4 cylinders Volvo! Group A Volvo Specs
On the car equipped with a single lambda sensor and a rudimentary CIS system,
“Vampire” ant-knock processor is a cheap engine Life Insurance and is always worth implementation, even if you leave your car “stock” (for explanation WHY - see my post # 68).