On Wed, 23 Jan 2008 16:30:53 -0000, Gary Fritz <fritzxxx@[EMAIL PROTECTED]
>
wrote:
>still just me <wheeledBobNOSPAM@[EMAIL PROTECTED]
> wrote:
>> Saab builds in a "don't boost quickly in low gears so no one get's
>surprised" program in the factory computer ...
>
>Now that's interesting. I haven't heard that before. My '02 9-5 Aero is
>an absolute *dog* off the line -- I have accidentally chirped the tires
in
>a 9-3 turbo (and even in a rental Nissan Sentra!!) because I'm so used to
>punching it hard to get the 9-5 moving.
The Saab programming does not cause the initial problem - no boost at
idle. That's a "feature" :-) of a small turbo motor. The programming
does restrict boost in 1st & 2nd gears. The idea behind this it to
prevent serious boost from build in the low gears where you can spin
the tires and/or have more trouble controlling it. it's supposed to
make the Saab drive more like a normally aspirated engine with no
turbo surge. In higher gears, that isn't an issue and there's no
serious governing of the boost above 2nd gear aside from an overall
limit on max boost.
>Once you ****ft into 2nd/3rd it doesn't have this "no power" issue, but
even
>then there is a HUGE turbo lag, 1.5-1.7 sec or more. This happens after
>each ****ft and I've never come up with a way to keep the turbo spinning
>between ****fts.
>
>Could this "don't boost quickly in low gears" program be the cause?
Though
>it may be a moot point, as it looks like new ECUs run $1000-1200, and I'm
>not eager to dump that much into an experiment. It looks like most
>aftermarket ECUs are mostly aimed at increasing horsepower, and I *don't*
>need that. Once the turbo finally spins up there is PLENTY of
horsepower.
>It's just the "starting out in 1st gear" and "long lag after hitting the
>gas or ****fting" that are annoying.
You should understand first that your Saab engine is capable of
producing much more HP. The turbo produces boost on a relatively fixed
schedule depending on how fast it's spinning. The amount of boost that
gets to the engine is determined by the opening or closing of the
waste gate (when open, it dumps excess boost).
The programming of the ECU controls the waste gate, as well as the
ignition timing of the engine and fuel delivery. Your Saab can create
more HP, or more HP faster, simply by leaving/keeping the waste gate
closed. Saab has the waste gate programmed to be very open very
quickly in low gears to avoid a fast buildup of boost.
ECU upgrades typically provide more HP by letting the boost build
higher before dumping it (by controlling the waste gate). But, they
also provide more boost *faster*, by keeping the gate closed initially
until boost builds. The Saab factory program opens the gate quickly,
even at low boost, to keep drivability more the way most buyers expect
it. Some of us don't need that mothering :-)
Note that Saab itself sells ECU upgrades now. Factory boost is about
11psi, I believe the Saab upgrades and the stage 1 aftermarket
upgrades hit about 14psi. ECU's can reprogram that upper limit though.
People who do heavy mods head higher to 18-22psi but have to do other
mods to increase airflow through the engine like larger down pipes.
Around that you start to need larger injectors to supply more fuel -
the turbo really gives us all the air we need... but we run short of
fuel.
There is also the MBC or Manual Boost Controller. This is a mechanical
device which bypasses the ECU's control of the waste gate. It does the
same thing a reprogrammed ECU does, but mechanically. It's cruder,
since the ECU can be programmed to specific boost and timing curves...
the MBC just creates a mechanical arrangement whereby the gate stays
closed until a max boost setting is hit. The MBC also prevents the
engine from reducing boost if the engine knocks (although the stock
ECU will still control timing as best it can if it detects knock). The
MBC needs to be detuned slightly to avoid problems with seasonal
temperature changes or you need to manually retune it a little when
the seasons change (Fall to Winter, Winter to Spring) The MBC is not
ideal, but it costs about $35-$50 vs. $500-$800 for an aftermarket ECU
and slightly more for a factory-aftermarket upgraded ECU.
Back to your specific question: would an ECU (or MBC) upgrade help
with the lag? The general answer is "yes", because it will give you
more boost, more quickly. At the same time, it will also increase the
upper end boost. Will it be enough of a change to be worth the money
to you? Most people think so, but beauty is in the eye of the
beholder... so it is a little risk. You could try an MBC if you are
just a little mechanically inclined and if you like the effect, and
want a more proper solution, jump into an ECU upgrade.
.. smooth and gradual, no wheel spin. But, they also , or the same
boost for a longer time before they open the waste gate and vent it.
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