Date: Mon, 27 Mar 2000 09:01:46 -0800
Reply-To: BRENT CHRISTENSEN <bchristensen@INFOGENESIS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: BRENT CHRISTENSEN <bchristensen@INFOGENESIS.COM>
Subject: Re: Why did this mod increase my fuel economy?
Content-Type: multipart/alternative;
I suspect that is that this related to the same reason that my 2.1L Syncro
gets worse gas mileage that a 235 hp Chevy 327-powered IH Scout I used to
have (it averaged about 17-19 on the highway with military axles and 35"
tires, even towing a trailer). The Syncro is underpowered, and forces you
to drive at WOT a lot of the time. With more horsepower and torque
available at lower RPMs, your driving habits are altered and you end up
having to "push" the car less, resulting in better mileage.
Smooth driving results in better mileage, all other things being equal.
(I should mention that the aforementioned Scout started with a Holly 4
barrel 750 cfm carb and only got about 12 mpg until I switched to a
Rochester 2 bbl unit, which gave better low-end performance)
Brent Christensen
'89 GL Syncro Westy
Santa Barbara, CA
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM]On Behalf
> Of David Marshall
> Sent: Sunday, March 26, 2000 10:22 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Why did this mod increase my fuel economy?
>
>
> Volks,
>
> First a little background on my vehicle:
>
> - 1988 Syncro Transporter (Double Cab)
> - 225/60R16 tires (~27")
> - 2.0L 1995 Jetta engine
> - 1.8L Cylinder head from 1986 Jetta
> - 266 degree cam
> - Timing set to 10deg BTDC
> - CO set to 1.5%
> - 87 Octane fuel
> - CIS Fuel distributor from 1979 Audi Fox
> - CIS-E knock sensor (ignition timing) from 1987 Jetta GLI
> - Scirocco 16V fuel injectors
> - Audi 5000 turbo warm up regulator
> - No cat, free flow exhaust
>
> Proior to my modification I was getting ~15L per 100km (16 US
> mpg) in town
> and ~13L per 100km (18mpg) on the highway doing a constant 100km/h.
>
> The modification that I did was very simple. Ever since I
> installed the
> ABA (formerly 3A) engine I have been too lazy to modify the
> throttle pedal
> linkage so the throttle valve would open fully when the pedal
> is all the
> way down. Performance was good and fuel economy was nothing to be too
> concerned about. The problem with this setup is the 2nd
> butter fly (larger
> of the two) in the throttle valve would open only part way (75%). The
> solution to this was to install a small bolt and nut in the
> linkage of the
> throttle valve so 2nd butterfly would open sooner and all the
> way open when
> the pedal was fully depressed. Normally the smaller
> butterfly open 75% of
> the way before the larger starts to open - with the bolt in
> place it starts
> to open at 50%. The result was a much more snappy drive with
> a noticable
> "push you into the seat" feeling when you are accelerating as
> the thottle
> would go wide open a lot sooner and in a non linear fashion.
> The first
> fill up I did after the mod I got about 8L per 100km... I
> figured I must
> have missed recording a fill up so I thought nothing of it.
> On saturday I
> drove from Quesnel to Prince George on 11L of gasoline - this
> was a 125km
> trip through rolling hills at a leasurly 95 to 100km/h - this
> translates
> into 8.8L per 100km (26.7 US mpg)- the trip back we did a
> little more speed
> ranging from 100km/h to 115km/h plus really pushing hard in
> 3rd going up
> some of the steep hills - we consumed 14L of gasoline or
> 11.2L per 100km
> (21 US mpg).
>
> So, why did things get better with a throttle that opens
> quicker? Not that
> I am complaining!
>
> -- David Marshall - - Quesnel, BC, Canada --
> -- 78 VW Rabbit, 80 VW Caddy, 84 VW Westie, 85 VW Cabriolet --
> -- 87 Audi 5000 Quattro, 88 2.0L VW Syncro Double Cab --
> -- David's Volkswagen Home Page http://www.volkswagen.org --
> -- Fast Forward Autobahn Sport Tuning http://www.fastforward.ca --
> -- david@volkswagen.org (pmail) or vanagon@volkswagen.org (list) --
>
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