Date: Mon, 20 Dec 1999 22:02:01 -0800
Reply-To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject: Re: Unleaded Regular or Unleaded Premium?
In-Reply-To: <385EE9E3.86F1101B@whidbey.com>
Content-Type: text/plain; charset="us-ascii"
I would have to somewhat disagree with that statement - under "normal"
driving conditions you could get away with 87 octane in these 10:1cr
engines. I ran my 1980 Rabbit PU with a 2.0L ABA engine for an entire
summer without a knock sensing ignition. I used 94 octane Chevron fuel and
set the timing to 6 BTDC at 850rpm. On your typical summer day (low 20s C)
there will be no knock. If the temps got to +30C there would be some knock
if you are stuck in stop and go traffic. Also at higher altitudes (Rockey
Mountains) there is knock if you push it, even with 94 octane. This was
all done using a 1982 Rabbit Distributor with vacuum advance and vacuum
retard - generally considered the best performance non-knock sensor
distributor. If there was a knock sensing ignition present, there would
have been no knock as it would have retarded the timing until it
disappeared - thus giving you less power. With 87 octane fuel in a high
compression motor (with a knock sensor) you will not see any knock while
driving (unless something is not adjusted correctly). With the car at idle
and the oil at 80C static timing of 6 BTDC will result in no knock. Bring
the engine under load and you run the risk of knocking, especially if it is
hot outside. The ignition will compensate and retard the timing - a loss
of power will result. Running higher octane fuel will reduce the frequency
of knock and allow your timing to be more advanced most of the time. The
factory setting for most of the 10:1cr engines is 6 BTDC. You *can* set
these engines to 10 to 14 BTDC and see a 5 to 7% increase almost the entire
RPM range. The theory behind this is the knock sensor WILL retard the
timing under load at the lower RPMs (to around the factory +6 BTDC), but as
the engine starts to go up in the RPM band it is less prone to knock - the
computer advances the timing due to increased RPMs, now there is no knock
and the computer will increase the timing to the fullest (6 more degrees
than normal) to gain more power. Some ignition systems up to 30 degrees
advance can be seen (total of +36 with a static timing of +6), on systems
with +12 BTDC timing total advance goes to +42 hence 5 to 7% more power and
torque. I like to compair 10:1cr engines to fine wine - the experience
is better if you drink it out of a wine glass as opposed to a tupperware
container! Same goes for the gasoline you put into the engine, the
experience is better with more expensive gasoline. There is one catch
though... high octane fuel has less poential energy than low octane fuel,
so you need to burn more of it to do the same work (especially if there is
alcohol in the blend)... that is another thread!
At 06:45 PM 20/12/1999 -0800, Dana Morphew wrote:
>List, I followed Doktor Tim's advice and called Campbell/Nelson, a local
>VW dealer in our area, about what octane fuel the RV, HT, RD, PF, 3A or
>ABA engines from VW (all with high compression and knock sensor)
>require. Their service dept. said these engines will all do fine with
>87 octane with no degradation in performance. So there we have it...you
>can have your cake and eat it also.
>
>-Dana-
>
>
-- 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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