924 Garage "
... the best handling Porsche in stock form.", Jim Pasha, Excellence
David's Carrera GT Replica Project
David Frank has developed a kit for purchase. You can get all the details plus pictures of his car and the installation at his D.I.Y. 937 Carrera GT website.
About the car: The Carrera GT replica is built on a 1978 chassis. The body components are all A.I.R. fiberglass. Drivetrain and suspension are from a 1980 931 Donor car.
Modifications: Installing the 951 intercooler behind the front bumper
and routing the charge air tubes through a crowded engine compartment
presents some challenges. The prototype tube shown in the photo (Turbo side)
is hitting the hood and will need additional Modification. Mechanism that raises
and lowers the headlights will be replaced with non opening GTS type headlights. Fuel
distributor may need to be relocated closer to the center.
Adding a hydraulic clutch to a car equipped with a manual pedal and cable was accomplished with a custom adapter fabricated on the steel support for the intake manifold. The "lever" which engages the clutch cylinder was made from the 931 pedal.
Future plans for this project are the GTS headlights and some kind of vent or louver to cool off the turbocharger when the car stops moving, something more than the SCCA hood vent on most cars.
Following section reports the results of measurements of intercooler function:
Two temperature probes installed. The first one measures the air temp exiting the turbo. It is a digital Temp probe used for cooking with a stainless probe. The second Temp probe is a digital indoor/outdoor with the thermocouple installed inside the rubber banjo at the throttlebody. It reads the charge temp after intercooling.
With the boost at 9 psi the temp at the compressor soars to 150 F. within seconds at boost. Ambiant air temp at 60.F Temp at the throttle body max's at 67.F There is no sudden temperature spike after the intercooling (I thought there would be). Even in traffic with the car not moving the charge temp drops dramatically. The intercooler has tremendous heat sink ability. That was suprizing. I had originally intended to install ducting to force air through the core, but the results of my experiments indicate it may not be necessary.
Cooling the charge air creates additional HP in several ways: The first
and obvious being that a cool mixture is more dense. The second being that additional
boost can be added because the
detonation threshold has been pushed back. The speed at which the fuel mixture burns doubles with EVERY 18.F rise in temp. The pressure drop accross the intercooler is slightly higher than 1 percent. Contrary to what you might read this does not drop the boost because the wastegate is sourced AFTER the intercooler. With the boost at a conservative 10 psi the intercooler setup should yield AT LEAST 30 hp over the stock U.S. setup and still maintain the same or greater reliability/thermal stress. Although certainly not a simple installation, Adding the 951 intercooler (or any other intercooler of the same size-efficiency-etc) is absolutely the best performance upgrade you can do.