Date:         Sat, 27 Nov 2004 15:59:32 -0800
Reply-To:     syncrolist@BOSTIG.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Bostig Engineering <syncrolist@BOSTIG.COM>
Subject:      Re: Intake air flow, improvement possible?
In-Reply-To:  <001401c4d4d3$fb61dfe0$e10cfea9@9100d>
Content-Type: text/plain;charset=iso-8859-1

Hi Gary,

You make some good points, but let me clarify a couple things.

> 1. The volume of air required by a gasoline engine is directly
> proportional
> to RPM.
> The higher the RPM, the more air needed.  A gasoline engine needs to
> maintain a relatively constant air fuel ratio.

True, however above and beyond the volume, we're really concerned with air
mass, which is derived from volume as you point out, temperature, and
pressure. It is the mass of air not just volume that affects air/fuel
ratio which like you say, the ECU likes to try to keep in range. This is
the primary problem with the vanagon stock system, it measures force on
the vane spring(crudely measuring volume), and tempurature, and then back
calculates mass. This is the reason why vanagon guys have problems at
altitude, because the stock system isn't *measuring* mass and does not
calculate the value correctly when not at sea level.


> 2. The stock air filter - throttle body - intake manifold  system is
> capable
> of flowing enough air for the stock engine up to redline.

True, but any given intake system, isn't just qualified for flowing X CFM,
at X pressure drop. The vanagon system at the CFM needed by a running 2.1
at redline creates about a single PSI of drop. This is in effect running
your engine at well above sea level. At lower flow, it isn't as much of a
drop, but it's significant enough to make a substantial gain in power
possible by increasing flow and decreasing that drop. Think of it this
way, do you get more soda by sucking the same through a wendy's straw, or
do you get more by sucking through the sewer pipes they give you at
McDonalds?

> > So, increasing the volume of air the intake tract can flow will have no
> affect on power or fuel economy (in a stock unmodified engine).

Again, we want to talk about mass. not volume, as I could put the engine
in a vacuum chamber at 1 PSI, and you'd pump the same volume but couldn't
produce 20 HP.

> > If you drive your van at less than redline, increasing the size of the
> throttle body and/or increasing the size of the intake tract will have no
> affect
> on performance.

It has an effect in multiple ways, not only is the pressure drop reduced,
and mass increases, but the volumetric efficiency of the engine increases
because the exhaust backpresure (which is always at or higher than
atmospheric) to intake pressure ratio is closer. Additionally pumping
losses will be less as a result of not having to suck air from a lower
pressure and pumping into a higher presure (intake to exhaust).  If you
don't buy this stuff, I'll hook you up when we're shipping and you can
feel it for yourself :)

 Certainly everyday city driving is far below redline,
> well
> within the capacity of the stock AFM and air filter.  Even if the stock
> system is
> restrictive, there should be lots of headroom for normal driving with a
> stock engine.

True, but this is akin to saying you don't need/want more power, which is
a personal thing.

> If you do not accept the above, then some related questions are:
> - just how bad is the stock system?

So bad that when we flowed it the first time, we had to go back and triple
check because we didn't believe the bench... and so bad that I don't think
it would be possible to find a system that performs this badly on ANY car
produced today.


> - do things like K/N air filters really honestly offer more hp and better
> mileage?

They can, but the entire system has to be considered as a whole, and just
the K&N while in one application yields great results, may not in
another... but basically the answer is yes because the surface area of the
filter is much higher lending itself to better flow/less drop... now just
to compound your head scratching... and for everyone on the list to
consider.. brownie points to anyone that comes up with the correct anwser
to the following FACT:

WHY does the vanagon air box/meter flow BETTER with an air filter, than
wide open without one?  :) (While we're on the sibject of filters and
flow)


Hope this helps,

Jim Akiba
Bostig Engineering