[BiturboS4] ??? about mods, boost gauges, and other exciting stuff.................

Ian McCloghrie ian at codrus.com
Wed Sep 18 11:22:56 EDT 2002

On Sep 18, 2002 jysap at cs.com wrote:
> When adding chips (Kokeln) chips to my 951, the overall
> recommendations on Rennlist (Porsche/BMW msg board) was to add an
> AFPR (Adjustable Fuel Pressure Regulator), Boost Gauge (many
> vendors), Air/Fuel Mixture Gauge (too know if u r running too lean
> under boost), and updated Boost Valve (the Porsche guys also use
> Forge - but I choose the stock 993 valve - direct replacement for a
> 951).

An AFPR is only needed if the stock injectors cannot deliver the
necessary fuel at the stock fuel pressure.  Presumably on the S4 they
have enough additional capacity to handle extra boost, so the new chip
can just hold them open longer.

A boost gauge is a useful debugging tool, it gives you information
about the health of the system.  But it's hardly critical, and once
you know the way the car behaves at a given boost setting, there's not
much reason to look at it unless you think there's something wrong.

AFR gauges are something of a mixed bag.  Narrowband O2 sensors (which
is what pretty much all cars come with stock) have limited use outside
of a very small range around stoich.  They also tend to get confused
by high boost settings.  They are limited cases in which they're
useful, but mostly they're just pretty lights.

Upgrading the bypass valves probably isn't a bad idea if you're
voiding the warranty on your S4 already.  IMHO, if you're keeping it
stock, then keep the bypass valves stock and have the dealer replace
them under warranty when they fail.

> Is the S4 head gasket so strong that a lean fuel mixture indicator
> (under boost) is not necessary, thus eliminating the need for a
> fuel/air mixture gauge?

No.  Head gaskets are, to a certain extent, designed to be weak.  It's
a sacrificial part, you'd much rather the head gasket failed when
there was too much pressure in the combustion chamber than, say,
cracking the head.

> I guess my point is - if this points are recommended when chipping a
> 951 (a turbo car) - why not - when chipping an S4?

See above.

FYI, if you haven't read it already, I highly recommend the book
_Maximum Boost_, by Corky Bell.  It contains lots of excellent
information about turbos, and IMHO should be required reading before
modifying/adding a turbo system on a car.

'99 Mazda Miata LP FM2 Turbo
'01 Audi S4

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