Date: Sun, 3 Apr 2005 18:12:01 -0600
Reply-To: Martin Jagersand <jag@CS.UALBERTA.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Martin Jagersand <jag@CS.UALBERTA.CA>
Subject: Re: re diesel injection pumps
In-Reply-To: <20050403212346.FARH1796.tomts6-srv.bellnexxia.net@mxmta.bellnexxia.net> (message from Ben and Natasha on
Sun, 3 Apr 2005 17:23:46 -0400)
Hi Ben,
The swap you are doing is quite interesting. Putting in a 1.9l TDI block
while keeping the simpler and easier to understand/maintain mechanical
injection pump from the 1.9l TD. You should be able to gain the higher
efficiency (more power and lower fuel consumption at the same time!)
from the TDI, while maintaining the simplicity of the TD setup.
As you mention there will be some difficulties in getting the pump
tuned right to work with the new block. The most important difference
between the blocks is that the TD injects the fuel in a pre-chamber
(or swirl chamber), from which (with a bit of delay) it is pressured
out into the cyliner. In the TDI it is injected into the cylinder directly
(DI = Direct Injection). The latter gives much better thermal efficiency
simply because there is less surface area in the combustion chamber
to absorb and dissipate the heat energy. Hence more of the heat energy
is converted to pressure driving the piston downward.
Now to make the DI engine less Diesel-sounding and palatable
to the average auto buyer, VW introduced some innovations:
1. A dual stage injection. Pre-injection delivers a small fuel amount
to start rising cylinder pressure gently and prepare for the main
injection.
2. A 5 hole nozzle that spreads the fuel more evenly in the cylinder
than the 1 hole conventional style nozzle.
3. A specially shaped indentation in the piston to aid in the mixing
of fuel and air. (In combination with the TDI head)
4. A computer controlled electronic injection pump that replaces the
good old mechanical Bosch pump we all come to love.
Now the key question in your swap is how to make the TDI engine
work well without the new and complicated injection pump.
To answer that it helps to understand the purpose and function of the
innovations above.
Number 1. above helps simulate some of the time delay effects of
the pre-chamber in the indirect injection (IDI) engine.
Number 2 and 3 takes over the fuel-to air mixing duty previously
done in the swirl chamber of the IDI engine. Still the mixing
is not as good in a DI engine compared to an IDI. Hence the
DI has to run with much greater air excess than an IDI.
(so you need to keep the max fuel setting (smoke screw) to
about 20-30% lower.) This might seem like a power loss, but it
is compensated by the higher efficiency, (get same power from
less fuel). Also the TDI can take higher turbo boost pressures than
the IDI before reaching its thermal and mechanical limits.
Number 4 mainly fine tunes the timing of the pump to be optimal
for a particular rpm and load. To do this more precisely it uses
a needle lift sensor in one of the injectors. (which is one of
the common things to malfunction on TDI's)
The good news is that you can get 1 and 2 in your combination
engine by using the TDI injectors. Now it may still not work exactly
the same as Bosch tends to use different plungers, potentialy
different pressure rise curves, different delivery valves
etc in the different pumps. But I think it should work good enough to
an approximation.
Number three is already installed in your new TDI block. Notice
how a TDI head combustion chamber looks much more like a gasoline
engine head. This is because the special Diesel shape is built into
the piston, and not the head.
By not using 4 you will loose some of the precise dynamic timing
adjustment of the true TDI. This will affect noise and vibrations
a little, but is neglible in terms of power and fuel efficiency.
(Should you be inclined to experiment you
could try to first buy the deliver valves for the DI pump
and put them on your IDI pump. (Other possible combinations may
be to put the whole "head" ie the pump plunger and associated
body from a TDI onto an IDI. The head is available as a service
part at Bosch injection shops and can even be had aftermarket
from often dubious sources. Now this latter change I don't expect
to do much difference and would be more expensive.))
When you time your new combination engine I expect that you should put
the setting a bit more retarded for your combination than for
the conventional 1.9l TD. I don't know any better advice than
to try different settings and see when the engine "sounds right",
starts easily etc.
From: Ben and Natasha <benny_terry@sympatico.ca>
Date: Sun, 3 Apr 2005 17:23:46 -0400
Hello Martin,
I came across your page while searching for some info on the
injector pump on my VW. I just dropped a TDI motor into my 95
Golf, minus the injection pump. I used a non-electronic pump (the
original pump from the 1.9td that was in the car prior to
replacement) and am looking for some information on what
modifications need to be made to accomidate this setup. The car is
running, but has a lot of blue smoke coming out the back end. I
guess I need to turn down the injection pump, but am unsure how to
do this. Any ideas?
Check in order of importance (as suggested above).
1. Right (TDI) injectors?
2. Try different (retarded) timings
3. Fuelling settings on the pump.
Do you know of anyone using the
non-electronic injection pump in their TDI conversion? Thanks in
advance! Ben Terry
I bet many must have tried or thought of this. I'm forwarding
this announcement to the vanagon mailing list, where every now
and then some good diesel swap information and discussion is on.
The vanagon list is on a volunteer, commercial free list server.
There are also some Diesel specific lists, but I believe these
are on commercial servers that want you to register, combine
the list with advertizing etc. Someone from the vanagon list
can probably advice on this.
Some years ago I saw ads from someone trying to sell engines
made from TDI blocks and IDI pumps. I never heard from anyone
using one of these though, but they might be out there.
Your idea makes sense since a TDI block is no more expensive
than the IDI one. It might also be possible to make your
own 1.9 IDI into a TDI at rebuild time yourself by just
buying and installing the TDI head and pistons. I think
block dimensions otherwise are identical between the AAZ IDI and
at least some of the TDI.
Good luck,
Martin
http://www.cs.rochester.edu/u/jag/vw/
