My Biiig Project

[Jim Gathmann <jim_gathmann@xxxxxxxxx>]

--- "D. Dardalis" <dardal@xxxxxxxxxxxxxxx> wrote:
> Ultimately, you want to run
> the throttlebody 
> BEFORE the supercharger.

        Thought about that- causes a few problems, one being
damage to the supercharger when it isn't getting
enough air (with this type of supercharger, damage
will occur if it can't suck in enough, i.e. when TB is
closed).

  This way, your blower is
> not wasting energy by 
> compressing air which you then try to decompress
> with a waistgate.

        Wastegates are only with turbos.  The surplus air
rejected by the system I plan on tieing back into the
intake of the supercharger- as the air would have been
cooled via intercoolers before being rejected and thus
cold air would be going into the supercharger- so the
heating from the supercharger won't be as much-
followed by yet an additional pass through the
intercoolers generates perfectly cool dense air for
the engine.

        Also- on my engine, the RPM's required to get high
enough to need a blow off valve like that will rarely
occur- as the 3.3/3.8 V6's used in AC bodies (i.e.
Imperials) are low reving engines- mine has never gone
over 4k RPM.

 
> Also, are you sure you need
> alcohol injection 
> (since you already have an intercooler).  If you
> really do need it (I doubt 
> unless you plan to use 15 psi of boost), it will
> bring hell trying to 
> adjust your air fuel ratio (remember, alcohol is
> also a fuel!).  You may be 
> better off with plain water injection (only at WOT).
>  H2O is a bit cheaper 
> too.  Old WW2 aircraft used alcohol/H2O mixture
> injection at high boost to 
> prevent detonation, but the only reason the alcohol
> was in the mixture was 
> to prevent freezing at 30,000 ft+.
> D^2

        The compression ratio on the 3.3/3.8 is not designed
with boost in mind- adding boost without low
compression pistons and/or head shims will encourage
engine knock. Now since no one makes head shims or low
compression pistons for my engine, I would need water
and/or alcohol injection to prevent knock and as a
safety guard for the event of a lean conditions. Now
on my car (which uses an O2 sensor), the engine uses
the MAP (Manifold Air Pressure sensor) with the
computed RPM's and the oxygen level of the exhaust to
determine how much fuel to add- now with slightly
larger injectors and a fuel pressure regulator, this
will work perfectly at keeping A/F correct (I know
this from other cars with the same electronics which
have gone from N/A to boost). However this is not the
case at WOT when the O2 is ignored- and since my MAP
will only work to 1 PSI (single bar MAP), the computer
will have the system go lean during WOT- without
knowing it.

        Now since (for the most part) high boost levels will
almost always occur only during WOT and almost WOT
conditions, the added water and/or alcohol injection
will help deter lean conditions, and save the engine
from damage at the higher boost levels (and this will
in theory work according to an ex-Mopar techie I've
been in touch with on that part).

        Now I will have two additional injectors between the
TB and the intake manifold, triggured strickly by WOT,
lean readings, and specific boost levels- which
combined with the rest, should keep things all in
check.

        I would however have gone to the classic design of
superchargers if it weren't for the problem of space
in my engine compartment (my engine is sideways-
pistons are in line parrelle to the windshield and
bumpers). I thought about it- and even got detailed
measurements of all the classic supercharger designs-
all no go (wouldn't fit in there correctly). Now this
design will fit under the hood- which is nice, and I
can use my entire hood scoop for the big air filter.

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