Way better than a <leaf blower> (and stealthier, too!)

[Evan Arnerich <arnerich@xxxxxxxxxxxxxxx>]

I apologize for the size of this post, as my ISP doesn't offer any
server space for a web page. If you're not interested in the subject,
please page down and accept my apology for the WOB.

Driving to the hardware store the other day, I saw one of those jump
houses (the kind they fill with air and hire out for kid's birthday
parties) in the parking lot. The jump house is continually pumped air by
a suitcase-sized blower through a six-inch air hose. I measured the
blower and it's just the right size to fit in the trunk of my '81 E21
320i (see where I'm going?). If I mount the blower in the gutted spare
tire well, there's still enough room in the trunk for a small
gas-powered generator (to run the blower), and even room for a small
duffle bag for those weekend getaways. Throw in a can of flat-fix and an
air hose to refill flat tires (I've already got a source of air
pressure), and I don't really need to carry a spare. That should save
some weight.

I've tried a few dyno-runs with the whole thing set up on the floor of
the dyno room and can report that not only has the power of my little
1.8 liter increased 10%, but torque was approximately 12% over the stock
numbers also. That's 11 more horses, kids! Blows the competition away
(pun intended).

I figure I can run custom-made furnace ducting (with appropriate
adapters) from the air meter box back to the trunk (gotta cut some _big_
holes in the trunk floor!), then from the trunk forward to the throttle
body. My sheet metal man says he can make custom 2"x12" ducting, one
running under each side of the car to maximize both air flow and ground
clearance. The only problem is leaving enough clearance for driveshaft
movement and staying away from hot exaust components. For extra
filtering, I'll put in a reusable house-type furnace filter between the
air meter box and the custom ducting.

To handle the heat of the super-compressed air, I'll route the return
ducting up through the floor board (more holes!) and duct it through the
A/C evaporator to cool the air before it gets to the throttle body. How
about that for an intercooler! The only problem is that when the A/C is
on, it sucks about 12 of those 11 horses gained (I know, a net loss).
But if I relocate the A/C compressor to the trunk and run a belt to the
generator, I should be able to gain that back. I'll have to run A/C
hoses from the condenser back to the trunk, but those (as well as the
compressor) are getting replaced in the already planned R134a conversion
anyway.

To get air to the generator (_it_ has to breath too), I've removed the
rear-deck speakers, but left the grills. This will cause some air to be
sucked out of the passenger compartment, but it'll kinda be like forced
flow-through ventilation. I'll use the trunk drain holes to route the
generator exhaust. No ugly stuff sticking out of the trunk lid, so it'll
have maximum stealth potential. I just hope that between the blower and
the generator, it doesn't get too noisy in the passenger compartment. A
high-powered stereo may be on my Christmas list.

I only want this on at full throttle, so I'll mount an A/C
compressor-type clutch on the pulley of the generator which will be
triggered by the WOT switch. That way, the only time the generator will
actually produce power (thereby spinning up the blower) is when needed.
If spin-up is too slow, I'll investigate solenoid-driven dampers,
bypassing the blower which will be spun up constantly, ready when
needed.

As a bonus, I could throw one of those jump-houses (all folded up, of
course) in the back seat and make a few bucks on non-race weekends. I
could have all the hardware paid for in about 150 birthday party gigs.

Some questions: Will I have any turbo-lag with the length of my intake
tract? Should I be concerned about my air-fuel mixture? What about air
that gets into the intake through the inevitable leaks which won't be
measured by the air meter box? How much fuel will the generator consume?

Total cost: $1200 for the blower, $1600 for the generator, and a few
more hundred for miscellaneous stuff and it's in for about $3200. That's
less that $300 for each extra horsepower.

Wish me luck, I'll keep y'all posted.

R. Goldberg  '81 320i (soon-to-be stupid-charged)

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