[s-cars] Stock Boost Levels for Mark Rivera

[Dave Forgie]

Mark: From pg. 18 of the VAG Self Study Program Guide 143 regarding the
AAN 20 Vt engine, when compared to the former 3B 20vt engine in the 1991
200 20vt, "the nominal charge pressure was increased from the former
value of 0.82 bar to 1.15 bar...fast charge pressure rise is programmed
in the lower speed range, the so-called 'overboost', in order to have
especially good acceleration".

This make pretty good sense based on 1 Bar = about 14.5 psi, 1.15 Bar =
16.9 psi boost.  The 92 spec North American cars that came with the
digital boost gauge often see 2.1 Bar absolute and sometimes 2.2 Bar
absolute.  Assuming atmospheric pressure is 14.7 psi, this implies that
the boost would be 15.75 to 17.2 psi (right in the range of 16.9 psi). 

A stock K24 turbo is capable of a little more without becoming
inefficient.  An aftermarket chip set, e.g. MTM Stage 1, IA Stage 3, MRC
Stage 1, with the stock 2.5 Bar pressure transducer (MAP) in the ECU
case  and stock K24 will usually push towards 20 psi and about 260 to
270 hp.  An aftermarket chipset, e.g. MTM Stage 1+, IA Stage 3+ and MRC
Stage 2, with a 3.0 Bar MAP (or a VMAP set to 3.0 Bar) in the ECU and
stock K24 usually push towards 22 psi boost and 270 to 280 hp. 
(Sometimes a bit higher but this is really stretching the K24 and
producing a lot of heat).

When you go to an aftermarket turbo like the KKK RS2 turbo or a Garett
2876 or 3071, then boost levels can be taken well into the 28 psi range.
26 psi is a safer, more conservative level.  Upgraded injectors are
needed to make proper Air/Fuel ratios and the end result is in the 360
to 370 hp range.  It is definitely possible to go higher still.  

HTH

Dave F.