Zlet Derestricted Induction Modification - By Man-Chun Hui

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Zlet Derestricted Induction Modification - By Man-Chun Hui

Inlägg  mullcom i tor jun 12, 2008 9:51 pm


The first
time you use the power of the Z20LET it induces a big grin on your
face. But soon enough you start to wish for more power. On turbo cars
the cheapest and quickest route to power is upgraded induction system,
full exhaust and a re-map, these 3 things will give you a very good
gain. If you wanted any more power than these three modifications
will supply then be prepared to spend a lot more money. In this article
I want to improve the induction system of the Z20LET.

Induction System.

From the
above picture you look at the standard induction system and wonder
what Vauxhall was doing when they designed this induction system.
The air box and intake pipe is lifted straight from the 1.6, 1.8 and
2.0 16v engines and without testing I presume it’s pretty restrictive
for the 2.0 16v turbo engine. Then there are three 90 degree bends
(the pressure loss of a 90 degree bend is equal to 12 feet of tubing
with the same diameter!!) before the air enters the turbo. Then there’s
the big black pipe that goes over the engine and I’m pretty
sure the charge air is warmed by the engine before it enters the turbo,
all pretty bad for power and safety of the standard engine.

of Standard Induction System.

1) Restrictive
Cold Air Feed.
2) Restrictive Air box.
3) 3 x 90 degree Bends which has the same pressure loss equal to 36
feet of same diameter hose.
4) The black pipe going over the engine soaks up heat, which heats
up the charge air.


at the system we know it looks restrictive and there should not be
such a restrictive system on a performance car. But we have to measure
to see if the system is that restrictive, so how do I measure the
restrictiveness of an induction system? I have to thank www.autospeed.com
for the contraption I have built. It’s not pretty but it works.

Picture of system tapping into bit before turbo

The above
picture shows how the contraption is connected to measure the restrictiveness
of the induction system. This is a very sensitive device as 1 inch
of water is = 0.036 psi. The bit the contraption is plugged into is
normally a place for the for the boost solenoid to vent of excess

of system in car.

The picture
below shows a one way valve, this lets the system do its work but
once the water has reached its highest point the valve will stop the
water dropping back into the bottle so I can read the highest water
level without taking my eyes of the road.

of Air valve

Ok so
now we can measure how restrictive the system lets get some results.
I ran the car in 3rd gear up through the rev range a few times and
got the result of 6 inch’s of water in restriction.

of 6 inches of water

as you can see from the results there was restriction in the system,
but only 6 inch’s of water or about 0.22psi. Not a great deal
of restriction to be honest, but the higher your state of tune is
the higher the restriction would be.


My solution
to the problem is to use a 2.2 16v air box and remove two of the 90
degree bends on the system. As well as removing the two 90 degree
bends you also don’t get as much heat soak from the engine,
which should help a little with charge temperatures. Here is the list
of components.

Air box.

of Air box

C Turbo Diesel Air Intake.

of Veccy Intake
these items need to be modified to make them less restrictive, I rounded
any square edges of so the air flowed a lot easier over them and I
also derestricted the 2.2 box as well. The pictures are below.

2.2 Air
box Bottom Derestricted

Above picture shows restrictor pipe being taken out

Above picture shows edges smoothed off on bottom of air box.

2.2 Air
box Top Derestricted

Above pictures shows
restrictor pipe being taken out.

Above picture shows
edges smoothed off on top of air box.

Cold Air Intake Smoothed Off

The above picture shows
the standard Vectra intake, the plastic lugs are sawed off to fit
the astra. As well as the two major components you need:

- 90 degree
70mm > 55mm Silicon hose
- 45 degree 70mm Silicon hose
- Electrical Wires.
- Wire wrap.

The hoses
are needed to join the 2.2 air box to the turbo. The standard airflow
meter wiring isn’t long enough to reach the position I needed
it to reach. So you need to cut the original airflow meter wiring
and solder additional wiring on so the airflow meter can be moved
to the desired location.


The picture above shows
the standard induction system part disassembled. The easiest way I
found to take the system apart was to:

1) Take
out standard air box first; be careful with plastic tabs as these
are fragile.
2) Then take out standard cold air feed, you need a little bit of
patience with this as it’s a very tight fit. Once you remove
the screws move the whole air feed left and you need to pull, twist
and squeeze the pipe for it to come out.
3) The airflow meter is just clamped in place by the two hoses; handle
the airflow meter with care.
4) The engine over pipe is easy to take off but a picture below shows
the crankcase vent hose, this hose needs to be unclipped before you
can take the whole pipe out.

Pic of
Crankcase hose

originally wanted to run a hose from the crankcase vent back to the
induction system after the airflow meter but there just wasn’t
enough room so I decided to just stick a crankcase vent on it for

be careful with the turbo inlet as anything dropped down there will
be very hard to get back out, and might possible need your car taken
to a dealer for the turbo to be take apart !!!!!!!.
Pic of Turbo
inlet covered up


1) Starts
with the airflow meter as this is as difficult as it can get in this
article; if you are no good at soldering please don’t attempt
this. The simplest way is to cut and solder one wire at a time, this
way you can’t mess up (ok less likely too).
2) Once the airflow meter is done its time to move on to the Vectra
intake, the Vectra intake is pretty easy to put into place but before
you secure this put the 2.2 air box in and try the intake with the
air box and intake to air box hose in place. This way you can guarantee
a good seal between the intake and air box, once you have the Vectra
intake in the position you want secure it will some small screws,
you don’t have to drill the slam panel as there is plenty of
holes there you can use.
3) Ok you have most of it done now, make a cup of tea and drink!!
4) In this next section you need to cut and assemble the hoses and
airflow meter the 45 degree pipe is used from the air box to airflow
meter and the 90 degree hose is from the airflow meter to the turbo.
Don’t cut too much off to start with and take your time to position
everything nicely so it all seals well and has flexibility.

Pic of
completed system

When you have finished your system it should look similar to this,
minus the recirculating DV bit (In another article).


With the
trusty contraption plugged back in I tested the new system and came
up with 1-2 inches of water. Ok the standard system wasn’t that
restrictive to start with but now with the new system it’s only
causing a restriction of 0.035 psi – 0.07 psi, pretty good in
anyone’s books. On the road I’ve noticed a slight increase
in response and the car being a little bit perkier but nothing too
spectacular, the main thing I have noticed is the performance has
been more stable even after being in traffic (30 degree ambient temps)
and not such a decrease in performance from heat soak in traffic.



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