[Vwdiesel] 1990 Turbo diesel Fox 2 dr Wagon

[James Hansen]

VW opted for 23:1 solely for starting. Cummins uses 18:1 in their older
stuff, and they cold start accordingly... chug pop and fart until the
combustion chamber warms up, but comparing a 1.6 litre with one that has
more displacement in one cylinder than the whole vw isn't really fair
either. :-)  you don't even care about compression checks in a 14 litre,
it's all about blowby when evaluating the rings.  But, to start the 17 litre
cummins with 23:1 compression would require a vw for a starting motor, or
more in winter just to get it spinning, which is why older stuff had
compression releases to get them turning, and build up some momentum before
you started to squish all that air.

Running more advance is dynamically similar to having more static
compression- it effects combustion chamber pressure at TDC, which is pretty
much all of it- square inches and how much pressure on that area equates to
torque. The consequential longer burn time may give a marginal increase in
efficiency as well, as you get to use more heat in the combustion chamber to
push on the piston, rather than releasing it to the exhaust stream. How
manufacturers balanced off the lower compression ratio is by running higher
boost numbers, 30-40 psi boost in Cummins for instance... I suspect if you
ran more boost, you would have a happier engine with less timing, and vice
versa. 

When you say recommended pump setting, are you going off pump numbers? You
stated the engine wanted the cold start out, maybe the pump is one that need
more advance right from factory?

Have fun with it Brian. as long as you have egt post turbo of less than
1250, you're good.  Find yourself a big long hill so you can WOT load it and
keep it there for a while, just to be sure.
-james

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com] On
Behalf Of Brian and Ruth Decker
Sent: April-18-12 1:01 AM
To: vwdiesel at vwfans.com
Subject: [Vwdiesel] 1990 Turbo diesel Fox 2 dr Wagon

Hi Folks;

                I got busy so the Turbo Fox project was somewhat delayed. I
rebuilt a 1.6 turbo diesel engine that I had bought at an auction. It must
have been from an Audi or Quantum and had an automatic. Through the years I
have wondered why our 1.6 diesels had 23 to one compression and wondered if
they might run better with slightly less compression. Where I live in
Western Washington it doesn't get incredibly cold so I felt perhaps starting
with less compression might not be impossible. The block has 1mm over
pistons.  I took them to my machinist and he took enough off the tops of the
pistons to take out about one half of the swirl chambers. I reassembled it
with all new bearing, seals and a 3 notch head gasket (the thickest
available). We were guessing we might have about 20 to 1 compression. We put
new exhaust guides in the head plus new valve seals and lapped the valves.
It has a rebuilt injection pump and rebuilt injectors. It also has a two and
a half inch exhaust system and a turbo Quantum 9Q 5 speed tranny. 

                Now the fun begins. We set it up using the recommended pump
setting from our Bentley. The engine started somewhat hard and truly wanted
the cold start pulled. After warming up it ran pretty strong but was getting
about 32 mpg. I then started fooling with the idle settings and the fuel
screw. I have a pyrometer so was careful not to get the exhaust gas
temperature too hot. I could get good power but mileage didn't improve.  

                I finally decided that since I have lower compression than
stock perhaps stock settings weren't what the engine needed. We upped the
pump timing to 1.10 and  it ran better, started  better and the mileage
improved. We now are at 1.30  and the Fox wants to run hard, fast and the
EGT's are good. It loves going down the freeway at 70-75 and would happily
cruise faster if I wasn't afraid of the law. The mileage is around 45 mpg
running hard and fairly fast. We pulled the injectors today and did a
compression check and all cylinders are very close to 360 lbs. For some
reason it just loves lots of injection pump advance.

Brian Decker

Toledo WA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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