Turbocharged 968 engine by Anderson Motorworks. Check out the products > conversions site for pictures of my car and video of it on the dyno! This was before the mixture was tuned and only making 229 rwhp and 212 rwtq.
www.andersonmotorworksinc.com [copy and paste into browser]
If you recall John Anderson from Speedforce Racing [the chip stuff] then you should know he started his own business: Anderson Motorworks, Inc. He focuses more on racecars and performance engines than the broader aftermarket items that Speedforce specializes in.
Anyway, John called me last summer saying he wanted to turbocharge my 968. I sort of laughed and agreed it'd be cool, thinking he was only half serious, and I knew it'd be expensive if we did. He got right down to business telling me what he had in mind and I instantly realized how serious he was...we were going to turbocharge my 968. He wanted my car the same week so I drove down to San Diego.
We discussed the project over the phone and John proposed a conversion using entirely 944 Turbo parts. We wanted the car to remain as stock as possible while offering a REAL performance gain. We went over the parts that the conversion required. Of course we needed a turbocharger and a wastegate. John had a newly rebuilt K26/8 turbocharger laying on the shelf with a 993 compressor wheel. These are known as 'cheater' turbos because they look like stock turbos on the outside while offering better performance. We would need the 944 Turbo engine mount because this is what the turbocharger mounts to and drains oil from the turbo bearing section back into the oil pan.
The 968 oil pan drain bolt can be replaced with the 944 Turbo jetted drain bolt to receive the oil coming from the turbo mount feeding back to the oil pan. The oil source for the turbocharger is on the driver's side balance shaft cover, which would be tapped and connected to a factory 944 Turbo oil feed line which bolts to the top of the turbocharger. The 968 throttle body is actually water heated to prevent the throttle from freezing over on cold winter mornings, but this being a California car the throttle did not need these coolant lines...they would be moved downward 8 inches and fitted to watercool the turbocharger.
The next thing to address is powering the exhaust driven turbocharger. John figured we would need the 944 Turbo headers, crossover pipe, catalytic converter, and wastegate dump tubes. The 944 Turbo headers would require modification to the flanges because the 968's 16 valve head uses a 3 bolt pattern per exhaust port while the 944 Turbo head uses a 2 bolt flange. Seems like we would simply cut the 968 flanges off of the stock headers and weld them to the 944 Turbo headers. With the turbocharger driven we're producing boost, so the intake system would also require attention. We wanted to keep the factory airbox and run a custom intake pipe from the airbox to the turbo inlet using the factory MAF sensor. We would then run custom piping from the turbo to throttle, and this leaves the intake manifold.
The manifold itself proved to be the biggest dilemma. The factory 968 intake manifold uses a dual resonance 'VarioRAM' design that actually has 5 intake runners feeding 4 cylinders. Once a particular engine speed is reached the fifth runner is needed to direct the greater rush of intake air. Porsche engineered the manifold to overlay this fifth intake charge so that it resonates with the other four intake charges later in the manifold, actually resulting in low boost pressure to the cylinders. The problem with using this manifold was the physical size; with the fifth runner going downward and underneath to the back of the manifold, this area was required to mount the turbocharger. A custom intake manifold made of a 944 Turbo and 968 manifold was fused together.
So that was the basic mechanical part of the turbocharged engine. We would address tuning [fuel delivery and timing] after the engine was converted to forced induction.
John started by removing everything on top of the engine. While we were at it we also replaced the radiator to ensure maximum cooling efficiency with the added stresses and heat from turbocharging. The intake manifold was sent to Tim Richards and Speedforce Racing along with a 944 Turbo intake manifold. It was Tim's job to weld the 968 intake manifold flange to the 944 Turbo intake manifold. Meanwhile John installed the 944 Turbo engine mount and connected the oil drain system to the oil pan. He then removed the balance shaft cover and tapped a hole where the factory 944 Turbo line is tapped and connected the oil feed to the turbocharger. The down pipe was then bolted to the turbocharger and the turbo bolted down to the engine mount. Then the cooling lines were connected with no modification to any of the coolant lines.
With the car then lifted up we began working on the exhaust system. We decided to keep the 968 headers on the car. The problem is the flanges on the crossover pipe don't line up with the flanges on the 968 headers, so the flanges would need to be cut and turned to line up with the headers, then welded back on. The 968 exhaust system came down next and the 944 Turbo catalytic converter went on but there was an 18" gap between the Turbo catalytic converter section and 968 muffler. This is because the 968 uses an additional resonator in the exhaust system behind the catalytic converter to silence the exhaust, so Tim Richards at Speedforce later fabricated a 1 inlet 2 outlet pipe connecting our catalyst section with the dual inlet 968 muffler assembly.
The intake manifold was proving to be very difficult. With the 968 flanges welded to a 944 Turbo manifold the intake was too wide and didn't fit on the engine. The 968 has a 16 valve head with two camshafts and the 944 Turbo has an 8 valve head with one camshaft...therefore the 968 head is significantly wider than the 944 Turbo cylinder head and the manifold would need to be cut to fit on the wider 16 valve cylinder head. All three of us spent an afternoon devising ways to make the intake manifold work. Tim suggested a custom plenum but I wanted the car to remain looking stock. Tim then cut both manifolds in locations for the runners would line up. The manifold went back and forth between the car and work bench to clock each side so that the manifold would lay at the correct angle across the top of the engine. Too flat and it would hit the turbo, too much of an angle and the hood wouldn't close.
After trial and error we finally got a manifold that would physically bolt up to and fit on the engine. The next dilemma was using a 968 throttle body with the 944 Turbo intake manifold. the 968 Throttle measures 65 millimeters and the 944 Turbo plenum measures 2.25" or ~57 millimeters. Since the 944 Turbo throttle also measures 57 millimeters we thought this throttle would be a better match for the 944 Turbo intake plenum. The main reason for not using the 968 throttle body was it's physical size, it came too close to the coolant tank with our intake manifold design and the throttle arm itself was on the wrong side so it would be used upside down if used at all. Instead we decided on the 944 Turbo throttle with an adapter so it would work with the 968 throttle position sensor.
After the intake manifold was finalized John ran all of the vacuum piping from the back of the manifold. He also ran a line for the vacuum assisted brake booster and now it was time for the intake piping. Again Tim Richards at Speedforce was chosen to do the intake piping with ports for a diverter valve, and at the same time close the gap in the exhaust system.
All of us worked on the car until late before it was fired up at LAST! The car belched some smoke from the oil and coolant items that had been reworked. The car had race gas in it to hold us over until the car could be tuned and with that the engine was idled to operating temp before we got in and stomped it around the parking lot. The 968 made torque before but now it broke the tires loose at 3k RPM's in 1st gear...sure didn't do that before! The car was still a little rough because it was dirty as hell from sitting around for 6 weeks and the engine required necessary tuning and other bits. But the car ran, and the turbocharger was definitely doing its job. The minor details could wait until tomorrow.
...Will update the rest of this story later...
This isn't the most recent dyno chart but the one from last february showing 251 RWHP and 238 RWTQ. As you can see the mixture still wasn't right [this has been corrected with the latest chip and dyno tune] but the car is now making 10 more hp and lb-ft of torque. The red air/fuel curve is what the mixture basically looks like now, the green lines with black arrows indicate timing retard related to knock, and the blue circles are big changes in torque associated with corrected timing and the variable valve system shutting off at 5500 RPM's.
