|With the motor disassembled I had
some decisions to make. I had always planned to make some changes
while I had the motor apart. I also wanted to keep my overall
project costs as low as is reasonable. Here are some things I
considered in no particular order.
The 5 cylinder uses the smaller VW intake valve sizes used on non-GTI
cars up through 1988. I had hoped to change this head over to the
larger 40 mm intake valves vs. the standard 38 mm. I have solid
lifter valves coming out of my ears, but had forgotten that the Digifant
head (hydraulic lifters) that has been collecting dust for 2 years in my garage has 40 mm
valves. That means I would only have to buy one more ($22) instead
of 5. It turns out that the standard valve seat is too small in
diameter to work with the larger valve by about 0.5 mm. I guess
you could have the stock seats removed and install larger ones, but this
is outside the scope of my budget.
I had also looked at doing away with the sodium filled valves after
comparing them to the solid lifter exhaust valves I had on my shelf.
After further inspection the hydraulic lifter valves out of the
Digifant head are very similarly shaped and a few grams heavier so I
will be sticking with the stock 5-clinder exhaust valves. It is
strange because the older solid lifter exhaust valves are shaped much
nicer than the later ones. I guess short of getting custom valves
made you would have to cut down a set of solid lifter
valves. Maybe for some future project....
If you are willing to mix and match parts you can find later normally
aspirated 10v heads with 40 mm intake valves. If you are
interested in this search in the archives of the quattro list on Audifans.com. Make sure it will fit
on your block however. For example an MC head (later turbos) will
not fit on a KH block. Been there tried that.
Most people won't care about the weight of valves, but I thought since
I had them out I would measure them. They were all still a little
dirty with carbon so the weights might be off slightly overall.
*Solid lifter valves have slightly longer stems, but the exhaust valve
has a much smaller diameter stem at the back of the valve head (see picture on project intro page).
|70g (38 mm)
|65g (33 mm)
1.8L GTI (83-84) *
|77g (40 mm)
|64g (33 mm)
lifter - Digifant (89-92?)
|74g (40 mm)
|71g (33 mm)
This one I was back and forth on. Ultimate power in a turbo motor
comes from low compression and high boost, but low compression gives
poor off boost torque and in turn poor day to day drivability. Since I am looking for a fun car, but not a
rocket I kept the compression close to stock. If I
was planning to use programmable fuel injection like on my Race Rabbit
I would go higher with the compression. With the factory system I
am worried about detonation since I don't have control over the spark
When I started this project I had not realized that the KH engine had a
fairly high compression ratio. I had planned to deck the head some
to get into the low 8:1 range. Since the engine is higher than
this to start I just decked as necessary to get a flat surface.
In the end I think I took about 0.009" off the head, but in
reshaping the combustion chamber probably ended up with slightly
lower compression overall.
My technical knowledge of turbo motors before this project was very
limited. I have reviewed some of my old textbooks and read many
opinionated postings on the Internet. Correct or otherwise I have
come to the following conclusions:
I am looking for a motor with good torque, reasonable gas mileage,
minimal turbo lag and good power. First the gas mileage.
Obviously on boost I will use far more gas than I would in a NA
4000 motor. The efficiency of a spark ignition engine is driven by
its compression ratio. My current motor has 8.5:1 which is very
close to the KH compression. For minimal turbo lag I want to
minimize the volume of air between the intake of the turbo (compressor
side) and the intake of the turbo turbine (exhaust side). To get
the turbo to spin up quickly you need a strong temperature and pressure
delta across the turbo's turbine. This means keeping the heat in
the exhaust stream before the turbo and using large piping after the
Since most of my experience is with normally aspirated motors some of
this has been hard to get used to. For a turbo street motor equal
length exhaust runners is of no help and could likely hurt things as
this means more exhaust volume and more lag. The purpose of an
equal length header is for exhaust scavenging by creating low pressure
zones in the header. Well the last thing we want in a turbo
exhaust manifold is lower pressure zones. This made my life easier
as I had been planning to make a new header.
Like I said this section is my opinion and many others abound.
Every hand made exhaust header you will see for Audi I-5 motors
searching the internet will be a long runner equal length header.
While this is where ultimate power is found I don't agree that it is the
solution for a daily driver. I hope to add a section on
Exhaust Ports and Manifold
I have some exhaust gaskets from some VW application that have a
generous port hole. I don't know what they are from, but they are
bigger than the ones I took off the turbo motor. Below on the left
is a picture of this gasket on one of the exhaust manifold ports.
You can see that the hole in the casting is smaller and offset
from the gasket. This is also the case on the head side, but they
are generally better centered. The picture on the left is one of
the other ports that I have already gasket matched with a die grinder.
I blended it back as far as I could reach into the manifold.
On several of the manifold ports I have found that the opening is
actually the smallest part and it opens up slightly.
The collector side of the manifold also needs help in its stock form.
The picture on the left is how it came from Audi. I am sorry
for the poor quality of the picture, but I had already started porting
before I realized this picture was not so good. What is strange is
the size of the openings verses what is feeding them. The larger
opening in the lower right hand is fed only by cylinder #1. The
other two manage the remaining 4 cylinders. My main goal here was
to open up the top opening. I also blended the other two openings.
The opening in the bottom left corner has a sharp corner to turn
just before exiting and there is ton of material available for removal
here on the inside of the turn. I cleaned some of it up, but the
rest was hard to reach with the cylindrical burr I was using in the die
Additionally I have opened up the exhaust ports on the cylinder head
quite a bit. On the valve end of the port I found that the
machining to install the valve seat left very sharp edges and also
blocked flow out of the combustion chamber. In order to fit in the
head the exhaust port shifts to one side as it moves from the valve to
the manifold. I rounded edges and blended transitions. The
exhaust ports required a lot more work than the intake.
The valve guide blocks a great deal of the flow as seen in the picture
below. I had a little trouble getting a good picture, I may post a
different one later. Sadly the valve guide is already very short
so I did not feel comfortable cutting it down (plus it would be a lot of
work). I did however change their shape from convex to concave giving a
slightly larger cross section to the port.
You can see like the exhaust manifold earlier that the exhaust ports on
the head are much smaller and offset from the gasket. That has
On both the head and the intake manifold the gasket matches almost
perfectly with the head. The intake port size is already quite a bit larger
than a ported GTI head I was comparing it to. The ports are also
slightly higher on the head maybe to minimize the turn the flow has to
I found that at least with my head the quality of the casting was not
as good in the intake ports as in the exhaust. It was not as
smooth and the mold separation seams were more pronounced. As with
the exhaust side I had to clean up a little right under the valve seat
with some minor blending. I also tried to clean out some of the
As with the exhaust side the valve guide protrudes quite a ways into
the port with a casting bulge around this protrusion. I changed the shape
of these slightly as with the exhaust. There was a little more
room to work on the intake side, but I had to reach a little farther as
the intake port is longer.
As best I can tell the combustion camber is the same as other VW/Audi
motors of the era. I did not measure the volume of the head, but
compared it to some I have by eye. It is slightly different in
shape than the Digifant 10:1 head. Surprisingly the Digifant looks
to be slightly larger in volume. Below on the left is a picture of
the untouched combustion chamber. Next to it is a close up of the
exhaust valve seat. I found that the exhaust valve seat was sunken
more than the intake. This means the first few millimeters of lift
would have very poor air flow. The far right picture shows where I
carefully removed some material to bevel into the valve seats. It
took some time since I don't want to buy new valve seats so I had to be
very careful not to nick them.
These pictures are from my first head before I found it was badly
warped. I did similar work on the second head, but continued by
removing all sharp corners and then polishing the entire combustion
chamber after ceramic coating it. Edges and corners get hottest
first and lead to detonation, so I wanted the combustion chamber as smooth
as possible. I was careful to remove only what was necessary
since this will slightly reduce my compression ratio. The head
has been decked slightly to compensate for some reshaping I did in the
combustion chamber and to get a flat mounting surface.
Intake Manifold and Throttle Body
The KH motor turns out to have a
desirable intake manifold. The
single round throttle body makes upgrades to electronic fuel injection
easier as it allows room for a fuel rail where the spread bore throttle
bodies make it difficult.
The first thing I noticed about the intake and TB where the features
(or bugs) designed to make the single throttle plate feel like a
progressive spread bore. First the throttle plate has a huge ramp
on the back side to minimize the open cross section at low throttle
openings. Second the manifold has two huge lumps to further block
air flow at small throttle openings. Needless to say these are all
gone now. Below are some pictures of before and after. You
can see even the choice of fasteners for the ramp cause a large flow
The throttle is a little twitchy now as you would expect with a
single large plate. I think a conversion to electronic fuel
injection would help this.
Also you can see the after shot of the intake where I removed A LOT of
aluminum to do away with the humps. I also used a sanding
wheel with a long arbor as far up the intake ports as I could
reach. On most I was able to get at least 3 inches up. As I
recall the total runner length is about 12 inches.
Feb 12th Update.
Well a lot has happened since I last updated here. It turns out
my first head was unusable. I had noticed a crack between valve
seats when porting but this had not concerned me all that much. I
didn't really look the head over more than that. I got a call from
the machine shop and they said the deck was about 0.010" out of flat on
the gasket side and about double that on the cam side. When the
cam was placed in the head it rocked like a see-saw. The warping
on the deck side would not have been a problem as they could have just
machined it, but repairing the cam side would involve line boring and
inserting cam bearings. I am told there is no one in our area that
does that and I just saw dollar signs.
So I ordered another one from a local salvage yard. It turned out
to be the wrong part (my fault as I thought the motor was from an 86 car
until this week). The MC head from 86 to 88 motors will NOT fit on
an 85 block. Hopefully I will have the correct head (and head
gasket) within a week or so.
March 30th Update
I have had the new to me '85 head now for almost a month.
Extensive overtime at work has put this project on hold. My
confusion on the year of the motor also meant I had the incorrect rings
as '85 motors have slightly lower displacement (bore). I have had
a chance to work on the bottom end more since the last update.
With help from Blackdog
Motorsports my pistons now have ceramic coated tops and moly coated
skirts. Below is a picture of the now high tech pistons back in
the block. I have some other pictures of the pistons themselves
that I will get up sometime. The bottom end is most of the way
Below is the engine 95% of the way together. The coated
exhaust manifold is the only external sign of all the coating work that
went into the engine. I still have a few little things to bolt on,
but some of those will wait until it is in the car.