[Vwdiesel] 1990 Turbo diesel Fox 2 dr Wagon

[Andrew .Libby]

IMO removing material from the piston tops is a bad idea for a couple
reasons.  First, it removes the thermal coating on the pistons.  The other
reason (and also the reason using a larger than spec head gasket is bad) is
because it disturbs the "squish and quench" or the proper turbulence in the
combustion chamber (probably not a deal breaker on an IDI) and the transfer
for heat from the piston crown to the cylinder head during its time close
to TDC.  If you want to lower the compression ratio, a better way to do it,
IMO, would be to increase the depth of the cloverleaf pattern in the piston
crown or to increase the size of the pre-chamber in the head.

Andrew

On Wed, Apr 18, 2012 at 12:00 AM, Brian and Ruth Decker <
decker at toledotel.com> wrote:

> 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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