Re: Superchargers, EFI, & Twin Sparks

[bearbvd@domain.elided (Greg Hermann)]

>However...in #1034 Zamani Zambri brings up what many might consider a
>better reason, although what he says, does apply to turbos. So before I
>download his post, let me add that given the opportunity, I personally
>want more Instantaneous power off the line. No, I'm not a green light
>racer, just want considerable more oomph, for instance, when
>accelerating Up an on ramp without pausing (remember I have an Alfetta
>GT) losing considerable rpm, eventually shifting into 2nd, then trying
>to gain oomph again as I anemically motor up the on ramp onto 75 mph
>traffic.

One needs to be _very careful _ making such assumptions about turbo vs.
supercharger performance.

First--if one is dealing with one of the rather popular aftermarket
centrifugal compressor superchargers, their performance is even more
top-end oriented than that of a somewhat oversized turbo ! Their boost,
after all, varies with the square of their rpm.

Even with a more conventional, positive displacement type supercharger, the
facts of the volumetric efficiency and thermal efficiency curves of these
units dictate that there will NOT be the directly proportional increase in
bottom end "oomph" (read torque) which everyone assumes that they will give
!! The boost which such units yield is FAR from equal across the full rpm
band !!

I have played with the curves (and, yes, know how to use them properly) for
matching such units to a few different engines for the very _best_ of the
positive displacement superchargers (meaning the highly efficient, Swedish
patent, screw compressor type), and found that one needs to get the revs up
to a surprising degree before the boost will really come on !!

If you want virtually instant torque on demand, the forced induction device
which has by _FAR_ the widest "dynamic range" (yep, the same term as used
by audiophiles and controls engineeers, and it has the same meaning here
!!) of any of the usual options is a variable turbine geometry
turbocharger. One of these critters is easily capable of delivering FULL
boost by 1500 rpm, maintaining the same all the way to redline, and of
doing it with virtually zero response time.  For information on this type
of device, check out <www.aerocharger.com> , although Aerodyne is hardly
the only outfit making such turbos any more.

To think that you are going to get anything approaching optimum performance
and/or durability out of a boosted engine without making use of a fully
programmable IGNITION is nothing but a PIPE DREAM !!

The same applies to nearly as strong a degree to the need for a fully
programmable fuel injection system.

 Obtaining better atomization of the fuel than what is achieved with
typical electromagnetic fuel injectors (something more comparable to what
Webers will achieve) is also a very worthy goal, but that's a whole 'nother
story !

While you are at it, wide band O2 sensing gear is almost mandatory, EGT
sensing and logging capability are _very_ useful, and some sort of
detonation detection system is also all but mandatory. All of these are
very necessary during the tuning and "set-up" phase, use of any of them on
a "closed loop" basis during use/driving of the vehicle (such as is the
case with "auto tune" ) is not all it is cracked up to be.

Yes, the Autronics ecu's are very nice well thought out devices capable of
doing most of what is outlined above, although I think one might want to
step up to their next model above the SMU in their product line for a
boosted application. As for the lap-top question--yes, it is only connected
when actually tuning the engine.

If all of the above raised more questions than answers, you are probably
only inviting headaches, heartaches, and a _very_ sore wallet by playing
with a boosted engine without first seeking out seriously knowlegeable
advice !

Greg
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