www.944-20v.nl
When I started with this project there was little information to be found on the internet with regards to a Porsche 924 or 944 with an Audi 5-cylinder engine swap, and as such I’ve had to figure quite a few things out for myself. As such I hereby provide the information about how I went about solving certain issues. There may be easier or better ways, if so please let me know! :-)
What was clear from what I found online was that the 924 utilized an old type Audi 4-cylinder engine and that later longitudinally mounted Audi engines used the same bell housing pattern. This includes not only the 5-cylinder engines but also the V6, V8, and possibly even the V10 (not confirmed).
Engine
The engine that I’ve chosen is the 20-valve 5-cylinder (engine code 7A) that was used in the Audi 90 and Coupe around 1989 – 1990. This is a naturally aspirated engine and peaks at 170 hp. A question often asked is why I did not opt for a turbo 20v engine as these have a huge power potential. My main reason is budget, I could have the 7A engine cheap. Additionally I like n.a. engines better for use on the racetrack and the 170 hp will be enough to keep me entertained.
In order to get the 7A to work in the 944 I made several modifications.
Intake manifold and injectors
The original 7A intake manifold is formed such that its long intake runners curl over the engine and basically lie on top of the valve cover, where the throttle body is mounted on the exhaust side of the engine. Inside the 944 engine bay this is far from ideal. As such I have mounted an intake manifold and fuel rail from an Audi S4/S6 (engine code AAN) which has the throttle body mounted on the left side of the engine. This intake manifold fits without modification to the 7A cylinder head although a coolant hose connection also mounted on the cylinder head (but underneath the intake manifold) needs some modification to create clearance.
Because the intake runners of the AAN manifold are much shorter then on the original 7A manifold one might expect that low rpm power would suffer, but I have not recognized this thus far.
I have utilized the standard 7A throttle body and have made an aluminium adapter to mount this to the AAN intake manifold.
An additional advantage of the AAN intake manifold is that it accepts Bosch injectors. The 7A engine originally uses Hitachi injectors which have been proven to have bad fuel atomization and spray volumes differ from injector to injector. A 7A manifold can accept Bosch injectors as well but requires adapters to be used, for the AAN manifold Bosch injectors are plug&play. I currently use Bosch 0280150737 injectors of an Audi 200 20v (engine code 3B). Before these Bosch injectors can be used the injector resistor box as used for the original Hitachi injectors has to be removed and its wiring shorted.
Exhaust manifold
The 7A engine was manufactured with two exhaust manifold types, a cast iron one and a beautiful bundle-of-snakes header. Neither will work as they exit way to far to the back of the engine. As such I have made my own manifold.
Oilpan
The original 7A oilpan will not clear the 944 subframe and as such cannot be used, so I made my own oilpan. As I cannot weld aluminium, I utilized an old 10v 5-cylinder oilpan which is steel, and reworked it to resemble a similar shape as the original 944 pan. Capacity is 5 liters and oil baffles have been places around the pump pickup to avoid loss of pressure during hard cornering. Note that due to the different oilpan shape the oilpump pickup pipe had to be modified as well.
Engine mounts
Made my own out of steel.
Oil cooler
The 7A engine normally does not have an oil cooler. Instead of using an aftermarket kit I utilized the aluminium thermostat housing off an 5-cylinder 10v turbo engine which fits straight onto the 7A engine. I did have to mount this under a 45 degree angle (filter facing forward) to clear the 944 subframe, and this provides perfect access to the filter from the front of the engine. I picked up a nicely dimensioned oil cooler from a wreckyard and had the oil lines made at a local hydraulics shop.
Other
The engine itself got treated to a cylinderhead rebuild including new valveguides and lifters. Other then that the engine received all new bearings and seals.
Clutch
My 7A engine uses the standard 7A flywheel and pressure plate.
Bell housing
The 944 bell housing will not fit the Audi engine; the bolt pattern is completely different. Fortunately the 924 has a similar transaxle setup but this car used an Audi engine and as such a 924 bell housing will also fit the 5-cylinder engine. The ‘normal’ 924 has a cable operated clutch, but the 924 turbo, or 931, has a hydraulic clutch mechanism similar to the 944. As such, I used a 931 bell housing.
Not all holes between engine and bell housing line up, but there are sufficient that do for proper mounting. Additionally, some minor clearancing has to be performed inside the bell housing to clear the 7A flywheel outside diameter. I did this with an angle grinder and it took minimal effort.
I then found that the 931 bell housing was also not deep enough to house the 7A pressure plate, but this proved easy to solve as described next.
Spacer plate between engine and bell housing
Besides the problem of insufficient depth inside the bell housing I also found that the tip of the torque tube would not properly line up with the pilot bearing in the flywheel. I needed approx. 10 mm of spacing between the engine and bell housing to solve both issues. Upon going though an Audi spares catalog I found that Audi must have had a similar issue with one of their models, because it listed a 11,2 mm thick spaces, P/N 01E103551C. This part is used on the Audi RS4 with bi-turbo V6. I ordered the part and everything now went together smoothly.
Clutch plate
A 7A clutch plate will not fit the 944 torque tube. Going through a clutch manufacturers catalog reveiled that either a Ford Transit 2.0D or Audi 2.8 V6 would be the perfect fit. Same outside diameter as the 7A plate, but same diameter shaft and splines as the 944 torque tube. What’s nice to know, these cost a fraction of a 944 plate.
Clutch actuation
As said, the 931 has the same hydraulic clutch setup as the 944. Unfortunately that does not solve everything. On the 924, 931, and 944, the clutch is actuated by pulling on a clutch bearing rather then pushing as on a ‘normal’ setup. As such the level inside the Porsche bell housing cannot be used.
I went about solving this a rather odd way simply because I then did not know of the existence of an easier option I will describe next. I created a custom clutch fork with a new pivot point that used the original Porsche hydraulic actuator but then provides a pushing action working on a standard Audi clutch bearing. This works perfectly but was quite time consuming to make.
Another and easier way is to use a hydraulic clutch bearing such as found on some Fords and Saabs. This involves mounting the hydraulic clutch bearing to the bellhousing and running the hydraulic clutch line to it, and that’s it. I test fitted a Ford Mondeo unit recently and it looks like it would do the job.
Exhaust
My rear muffler is original 944 and the centre piece between rear muffler and exhaust manifold is custom made. The centre piece also includes a muffler and a flexible piece to allow some movement to relieve the manifold.
Cooling
I am using a stock 944 radiator and coolant reservoir. This setup has proves sufficient even during trackdays.
Below some pictures that I took during the build:
A freshly rebuilt cylinderhead
New mains and conrod bearings
The 931 bellhousing
Inside of the 931 bellhousing. Shown Porsche clutch fork cannot be used
The original 7A clutch plate next to the Ford item
Home-made header installed
Custom oil pan installed. Note also the stock 7A throttlebody on the AAN intake manifold
931 bellhousing installed on engine. Visible on the right side of the bellhousing the pivot point I made for the clutch operation fork
Note spacer plate between bellhousing and engine
Below picture shows the car at the inspection location for registration modification to 5-cylinder engine.
The car was also weighed at 1200 kg with 590 kg on the front axle and 610 on the rear axle. As such this engine modification retains the perfect balance the 944 is known for.
Email: 944-20v@live.nl