|
Unlike front engine rear wheel drive where there is vast amount of
transmission options. In the longitualy mid mounted engine and rear wheel drive,
the transmission options are
somewhat limited though it does not mean there are none. For transverse mounted
engines options are greater as front transverse configurations can be
transplanted in.
The problem goes even further as most of the front drive transmissions are rated
below 250-300hp. There is a number of Volkswagen / Audi transaxels that
are longitualy mounted engines with front drive or Porsche drive trains that
were designed with mid engine and rear drive. All transaxels between those
brands are interchangables with Porsche versions being build with performance in
mind and thus are more expensive and are capable of handling upwards of 500hp. There
are plenty of alternatives that are and can be
sourced from Europe where longituadly mounted engines are more common.
However with 400+ hp engine or not wanting to be replacing transmissions every
new season the options are far fewer and come at much greater cost. One has to
look at Porsche G50 or specialty racing transmissions ranging into $5,000
and above. Ideal speed of the car is compiled in this
calculator with number of other transmission models.
For the short coming the car is going to be fited with G87.20 transaxle out of
Porsche Boxter S and are known to be capable in handling up to 600HP with light
foot.
Another issue is with mating the transaxle to the engine. Since the Audi group
transaxel has pattern specific to the engines it does unfortunately bolt up to
the General Motors LS block. The solution to it is via intermediate adapter
plate that acts as translator with bolt holes for the engine and bolt pattern
holes for transmission. Clutch and flywheel are the next issue, it can be
positive or negative but in either way it is also required for the adaption. A
detailed information on making the adapter can be found <here>
Mounting:
Reverse switch. A very simple on/off switch capable of
handling upwards of 5A. Normally wired to hot in run (black/blue) and
switched leg (blue/red) going into lights. With 2 bulb setup this is sufficient
and does not require relay for higher current. A black/blue wire is looped
and extended to VSS connector for electronic sensors requiring positive voltage
for operation.
Wiring change
Black/Blue
Black positive
Blue/Red
Blue signal
VSS.
The Audi/Porsche produces 4 pulses per revolution of
axel using a very simple reed switch/sensor. At the time and type of
speedometers that was sufficient to produce a stable seed indication. Plus the
fact that it was only used for speed indication there was no need for greater
resolution. The connector uses brown wire connected to ground and
brown/red to the speedometer, a positive black/blue is not used.
We can work with the 4 pulses/rotation to setup our speedometer and can adjust
the GM ECM to accommodate the lower resolution, but there is a problem. The VSS
signal is used in the ECU controls idle, fuel control/pump and cooling fans.
So lower resolution would make the engine run irraticaly, possibly shut down or
run in limp mode.
To fix the problem we are using pulse multiplier. A small microcontroller
monitors period between pulses and multiplies it and feeds the multiplied pulses
to the ECU.
Wiring change
Black/Blue
Black
positive
Brown/Red
Green/Black signal
Brown
Brown
ground
Connectors
The Audi transmissions are using Junior Power Timer JPT AMP connectors. There
are 2 versions of them, the older ones where not water sealed aside of having a
rubber cover over the shell and they tend to corrode after few years of water
exposure. Newer design use rubber plugs that are around wire and cavity thus
having water sealing of each conductor and are of XG7035A / 282193 series.
Both older and newer shells are using standard 2.8 T078MF crimp terminals which
are easily available on many online stores
Older(original sensors use 3 and 5 pin connectors where are the newer sensors
use 2 and 4 pin connectors and are interchangeable with in the casing of the
transmission but harness needs to be modified
|
