So far I must have worked on it for 100 hours. After all, the welder’s bill
has already reached 11 hours (at AUD$50 an hour) and I’ve spent easily ten times
as much time on it as he has. In fact, having previously plonked a turbo late
model engine into an early model chassis, I’d say this project isn’t far away in
time and complexity.

And I thought it was going to be so easy…

The project is forced aspiration on my ’99 Toyota Prius. The Prius is a
hybrid petrol/electric car – but that unique driveline has absolutely nothing to
do with the time that I have so far spent. In fact, doing the same job on a
Toyota Echo would involve all of the same steps. (The Echo has an engine whose
bottom half is pretty well identical to the Prius.)

For forced induction I’d initially thought ‘turbo’, and in fact had found
exactly the right turbo going on eBay. A ball-bearing Garret GT12, it was new
but the private seller was quitting it after changing projects. Unfortunately,
he is also apparently one of those people who puts up eBay items with a low
starting price, then withdraws the auction at the last moment when the price
hasn’t risen high enough. And so wastes a lot of people’s time.

My thoughts then turned to supercharging. In the case of the Prius,
supercharging has distinct possible advantages – but then so too does
turbocharging! Given that no one in the world has forced aspirated a Prius, the
approach which would work best is problematic. But if I could pick up a small,
cheap blower, well…

Then while on a visit to Adelaide (surely the best city in Australia for
wreckers!) I bought an Aisin AMR300 blower, originally fitted to a Subaru Vivio.
It was physically small, at $200 the price was right, and the airflow capability
should match the Prius engine very well. So, just a case of making a few
brackets, bolting it on and sorting the engine management, hey?

Well, I haven’t got as far as the management (hell, as I write this the
engine hasn’t even turned the blower belt!) but the ‘bolting it on’ bit is
waaaay from the truth. To be frank, my appreciation of those companies that
develop supercharger kits has risen a long way.

Why? Well it’s simply not easy! Consider these points: the supercharger
mounts have to be rigid and strong; the mounts must bolt to very heavy duty
block and head fasteners; the pulley of the blower must line up exactly with an
existing belt drive (or with a new added crank pulley); a belt of the right
length needs to be available; the belt must be able to be tensioned; inlet and
outlet plumbing must be able to reach the blower; and of course the blower (and
belt and plumbing) need to fit into existing space. You’re saying: Yeah, so
what. OK then, go out to your car and find an underbonnet spot that
satisfies all those criteria!

With the Prius, I have less than 5mm clearance from the supercharger towards
the front, towards the back, towards the right-hand side of the engine bay, and
downwards. But sure, the Prius is pretty squeezy under the bonnet – but then so
too are lots of other currentish cars.

So what are the specific problems? Well, where will I start? Let’s try the
fact that the only way of adding a blower is to use the original Prius engine mount
bolts, so requiring that a new engine mount (now incorporating the blower
mounts) be fabricated. Oh yes, and since the original engine mount was a complex
casting, the new mount has to duplicate much of this shape – as well as
including the blower mounts, of course. Or perhaps you’d like to know that a
3-rib belt of the required length is not available? Or that tensioning the belt
by pivoting the blower on its lower mount isn’t possible because the inlet
plumbing will then hit an intake manifold stud and the solenoid that controls
the intake cam timing? Or you’d like to hear that the inlet plumbing path that
I’d chosen when designing the mounts proved not to be feasible when the blower
was bolted in place – clearances had just shrunk too much?

Or perhaps you’d simply like to hear of the mistakes I’ve (so far!) made? The
fact that, after all the brackets have been made, the blower now needs to be
moved 5mm laterally so that the belt lines up? Or the inlet plumbing fitting
which has been painstakingly bent and shaped, massaged with a ball-pein applied
to the copper until it fitted – but which has left way too little room for air
to pass within its confines? Or the belt tensioner bracket that I made (in 8mm
thick steel plate – the forces are so large!) that allowed adjustment of the
pulley angle but would have caused a big lateral kink in the drive-belt?

I am starting to think that a turbo conversion would have been easier –
despite the requirement to put an oil return line fitting into the sump and pick
up coolant and oil pressure. At least with a turbo, it doesn’t matter a damn
whether one end of the turbo is 5mm one way or the other, or whether the turbo
compressor is slightly higher than the turbine. And the rigidity of the mount?
Well, when it’s bolted to the exhaust manifold, a turbo will be plenty
rigid…

But today I think I had a win.

The belt tensioner is in place and even if it is on the wrong side (the
tension side of the belt, rather than the slack side), and even if it causes
less belt wrap around the supercharger pulley, at least it’s strong and rigid
and will be able to be adjusted with the blower and belt in place. And the
intercooler looks like it might now fit behind the bumper, although the current
mocked-up position does place it rather a lot behind the radiator for the power
converter (a heat exchanger which looks like a large oil cooler) and the
plumbing is tighter than I’d like. But at least the tube runs are much shorter
than the alternative going-around-the-headlights route…

And well, if my blackened finger-nail advertises to all its nascent pain,
that’s only to be expected when you jam it between a pivoting supercharger and
its heavy duty mount; and if Pete-the-welder is becoming more than an
acquaintance, that’s only to be expected when you’re at his place from any hour
from 9am to 6 pm six days a week; and if the concrete floor of the garage is now
covered with a Prius half-cut, a Prius up on jack stands, hoses and tools and
pipe bends and drive-belts and bits of raw steel, that’s only to be expected
when you take on a project that once upon a time, you thought would be a simple
three-day job…