Date: Sun, 16 Feb 2003 09:32:48 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: High performance fuel rail system.
Content-Type: text/plain; charset=us-ascii
The picture this fellow shows in his Ebaze auction is the rail from a
74-83 Air Cooled Type IV system; possibly less than 1/4" ID.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2403375533&
category=6764
This rail clearly could run short of fuel on each injector cycle and the
Type IV application uses a U type system with only one inlet to the fuel
pressure regulator.
Wasser Boxers have larger plastic chambers at the injectors that are
about 1/2" ID and incorporate a full loop system with a two inlet fuel
pressure regulator.
I believe that VW has addresses this low fuel availibility with the
larger fuel manifolds on wasserboxers.
In my case I addressed it by using a full loop system incorporating the
Wasser Boxer double inlet fuel pressure regulator and making the cold
start injector outlet dump to the second port on the FP regulator.
The reason for the changes I made were that the #3 cylinder was showing
lean burn on the spark plugs and running hotter than the other cylinders.
The full loop system corrected this problem on my 83 Air Cooled Van.
My fix cost me about ten dollars with the additional hose and a $5.00
used regulator from a wrecking yard.
If you're racing A porsche you might get some benefit from $175.00
lookem-good parts.
Stan Wilder
On Sun, 16 Feb 2003 06:45:12 -0800 Mark Keller
<kelphoto@HIGHSPEEDPLUS.COM> writes:
> Greg,
>
> The advantage or improvement with a larger fuel rail, is related to
> the
> localized low pressue variations that occur when the injectors open
> and
> close at high RPMs and High power settings.
>
> According to the Bosch Fuel Injejction, by Probst. It seems
> the pulsating effect is more pronounced as the interior volume of
> the
> fuel pressure rails get smaller. Therefore a larger volume of
> fuel
> under pressue in the rail, the less suspectable to localised
> pressure
> drop due to pulsation of the injector cycle, all things be relative
> to
> the rail volume and horspower being made.
>
> Keep in mind that Vanagon systems, all injectors fire
> simultaneously
> and therefore a strong draw on fuel. Starvation is somwhat accounted
> for
> by splitting the left and right cylinder banks with two fuel
> pressue
> loops. The first cylinders on each loop are # 2on the right and #
> 4on
> the left; leaving cylinders #1 and #3 in the downstream postion.
> Damage
> from Fuel starvation probably isn't a concern with a stock motor and
> a
> functioning fuel delivery system. Power drop off to the downstream
> cylinders could be as RPM increases.
>
> Just how high high a rpm? I don't know. I do know that
> thedigifant
> fuel injection pulse is nearly full time at 4000 RPM and up. The
> cause
> however isn't fuel rail volume, but rather is due to the low
> operating
> fuel pressue . In other words if the digifant system were to run at
> 50
> psi, instead of 36 psi, then the pluse cycle could be shortend at
> every
> RPM and the increase of atomization would improve the power
> produced.
>
> Back to the Fuel Rail. Even with 36 psi at high rpm and WOT, lower
> pressure whithin the rail occurs because of pulsation because,open
> closed cycle of the injectorslower localized fuel pressue being
> available to the injector n with . Any drop in fuel pressue and full
> power can't be produced. A good first step is to verify that the
> stock
> system fuel pressure at full throttle and 4000 RPM .. 36 Psi is the
> value at Wide open throttle, WOT. I believe this is critical to
> waterboxer power, since the system is engineered to be just
> adequate. A
> second step could either be a larger fuel rail or higher fuel
> pressure.
>
> Since stock is generally ok, just keep the system functioning well
> and
> to standards and power should be adequate. I do run a 50 psi
> system,
> and am quite please with it. I've driven well tuned stock systems
> and
> they really do quite well. The problem is that they require someone
> to
> calibrate them.
>
> Sincerely,
>
> Mark Keller
> 91 Carat
>
>
________________________________________________________________
Sign Up for Juno Platinum Internet Access Today
Only $9.95 per month!
Visit www.juno.com
| 
