[Vwdiesel] 1990 Turbo diesel Fox 2 dr Wagon

[Stephen Kraus]

Most Cummins engines have intake heaters to heat the incoming air in the
winter, so compression isn't as big an issue.
On Apr 18, 2012 8:45 AM, "James Hansen" <jhsg at sasktel.net> wrote:

> 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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