Supercharger info

[Chris Conlon]

Dan Zorde wrote:

> [...] info on the superchargers of the Toyota 4AGE engines.
> 
> Does anyone have a boost Vs rpm curve for this beast ?  or at least
> a rough  idea, so I know where to start with my fuel requirement calcs.
> 
> This is going on a Fiat 850 sport (903cc engine)

Head to Matti's site, a great Toyota engine resource:
http://www.students.tut.fi/~k124476/dataBySubject/Engine.html

There is a link to "Toyota Superchargers", where you'll see the SC12
is a 1200cc Roots-type blower. The actual boost pressure will depend
on the SC displacement, the engine displacement, and the crank vs.
supercharger drive ratio. Since this unit makes 8 psi (nominal),
feeding a 1.6l engine, driven 1.25x crank speed, you'd need to drive
it quite a bit slower to make similar boost on a 900cc engine.
(900/1600) * 1.25 =  0.70 times crank speed, for example.

The boost will be a couple psi even at low rpm, and will ramp up
pretty quickly as RPM rises to some value as determined above. It
should stay mostly flat, until the RPM gets high enough that the
torque starts dropping (on the NA engine). At that point boost will
start climbing again, since the head & cams are flowing less well,
and the air is backing up in the intake manifold.

Anyway that's a rough idea. This all kind of assumes an engine
with a decent-flowing head, and a typical torque curve, in NA form.

As far as EFI goes, efficiency & heating may be an issue, at any
kind of non-trivial boosts. If you're going MAP sensor, some kind
of temperature compensation is probably in order.

   Hope this is of some use,
   Chris C.