Re: bmw-digest V9 #547

[Brett Shortland <shorty@xxxxxxxxxxx>]

>>>>>>>>>>>>>
Date: Wed, 18 Nov 1998 21:42:21 -0800
From: Evan Arnerich <arnerich@domain.elided>
Subject: Way better than a <leaf blower> (and stealthier, too!)

....
 
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)
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Bwaaahahahahahaha
ROFLMAO

Oh dear, what we have here is well known in the automotive circles as a
Powered Induction System Strategy That Aces Kibort's Endeavor 
- - known in it's proprietry form as the PISSTAKE (Pat Pending)

Mr Goldberg (Arnerich?) has however added some nice touches to the PISSTAKE
with his notion of using the A/C evaporator as an intercooler.  I have some
ideas that may help him refine his system which may even allow him to
generate more power than he loses <grin> 

1.  To answer your first question, yes you will have some lag.  You may be
able to ovecome it by holding your foot down on the accelerator after the
last downchange into the braking area.  This will give the blower enough
time to pressurize the ducting and intercooler before you exit the corner.

2.  Tweak the evaporator themostat so that it cuts out at as low a temp as
possible without icing up the evaporator.

3.  Try installing an evaporator with a very large mass.  What can then do
is use a pressure switch in the airbox to cut the A/C out when it senses
that the blower is operating, indicating the application of full throttle.
The large cooled mass of the evaporator will still cool the incoming air
during the short full throttle runs.   This will allow you to leave the A/C
compressor in it's original location, so as not to upset the weight balance
of the vehicle.  It will also solve the problem of the net power loss.  ;-)

4. Piggyback a throttle cable from the accelerator pedal to the generator so
that it runs flat out at WOT when you really need it.  This will also reduce
the fuel usage of the generator by allowing it to idle when not required.

5. Fit a flap in the original air filter housing intake that opens with the
pressure from the PISSTAKE.  That way, when the PISSTAKE is not developing
extra air pressure, the air intake will revert to the original location
(behind the headlights) eliminating economy robbing losses during gentle
driving.

6. You will need to be very thorough to eliminate any air leaks.  I would
recommend Wurth Special Silicone 250 (the red stuff).  A 310 ml tube should
be enough  ;-)

7. Finally, a modified fuel pressure regulator should take care of any lean
burn condition on WOT...

As for generator fuel consumption, don't worry about it, just stick a 'T'
piece into the car's original fuel pump pick-up line.  That should supply
the generator with as much fuel as it needs.  Besides, we're talking
performance here, fuel economy should be of no concern.  ;-)

Hope that helps...

Brett Shortland
'82 535i - soon to be PISSTAKE'd   
:-)

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End of bmw-digest V9 #548
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