Stephen Kasper from Imagine Auto comments on my build

[Aggie93]

The PO (Don Cothard - former pelican) had Imagine Auto rebuild his car. I think it ended up being the prototype for what was called the "Stage 3" build. After the build Don and Stephen wrote an article for the local PCA newsletter. The link was posted here, but the link is dead.

Since Stephen does not post much here anymore, I thought it would provide a good summary of a lot of the mods that our cars have. Additionally, it could provide a springboard for how technology and best practices has changed since 2005 (when the build was done).

It is long and I had to break it up. I hope it is worthwhile.


I remember the first 930 I ever drove. Not only did I walk away with a full understanding of what vertigo mean, I also walked away with the car. I had known fast-everything from Mustangs with blowers to Porsches with blowers, even an RSR. At least I thought I knew fast, that was until I found the 930. In the last fifteen years I have owned over 30 Porsches and I have come to realize that even when you have found fast, you are never content with it very long.

Don came to me with the standard request. Make it better than before. Like BASF, I don’t make them, but I do make them (Porsches) better. Owning so many cars has given me a sense of intimacy with the cars that perhaps can’t be found unless you live with them daily. I love telling people I have driven a Porsche daily for the last fifteen years.

The first thing we did was to determine what Don’s goals were. He wanted more power, more drivability, better handling and a way to stop all the added power on a dime. We examined which RPM area needed the most power. The result is almost always the same, better low end, a better response time, and the ability to run with the best at the Glen. The goal when building a car is to make sure all the components work well together. Don had a few modifications already. The higher capacity intercooler was there as well as the exhaust. He had added a turbo that just wasn’t performing like Don was anticipating and was actually hindering performance, not helping. We decided that the best way to achieve Don’s goals was to look at each mod and how it interacts with the others. Keep in mind that the930 is a Constant Injection System (CIS) and is rather old technology, but it does work well. Because of the CIS, we had to with within the horsepower limits of this system.

Creating low-end drivability on Don’s car was simple. We added one half point on the compression to produce low-end response and to create the “snappy” feeling. We then added a set of custom JE pistons that were enlarged from 97 to 98mm. This increased the displacement from 3.3 to 3.4 liters and created low-end torque. Horsepower increase on the type of modification is rather small whereas drivability is the key. A cam was chosen that would add low-end power without sacrificing too much upper end. There is no free lunch. When you increase the lower end you also take away from the top. You must carefully match the package. So we now had our base. The car would have a great low end and torque with a cam that aided very quickly to the building of power.

On the top end, we first added headers. This removed over 4 feet of pipe to the turbo. The turbo responds based on expended exhaust gases. The faster the exhaust can reach the turbo the faster the turbo can come up to speed and create the added air to the system. The headers aid in that process and once again add a little horsepower, but huge drivability. The turbo that was chosen for Don’s project was one of the first of a new design. The prime of all CIS turbos has been the K27 7200. Originally installed on the Carrera 2 Turbo this set-up came on boost faster and harder and still yielded a nice 35 HP gain. The major difference between the C2T and the earlier turbos in regards to HP was simply the turbo and better ignition. For this usage and to satisfy our desire to continue making power on the back straight of the Glen, we needed something that would provide enough push without causing the turbo to stall out. The choice was a custom built turbo that was developed and assembled using all factory parts. The custom turbo retained the drivability the K27 is known for, yet pushed like the K29 on the top end. The design of the compressor wheel brings this turbo into the year 2004 without issue. The outcome was so grand on Don’s project, that this turbo has been put into production full time.

At the end of the day the package looked something like this…the added CR and displacement allowed the car to come away from a light with immediate response. As the low compression motor started to gasp for air, the cams picked up very quickly and in turn started the velocity of air to the turbo. The headers got the air quickly to the turbo and as the cams were hitting their ideal power spot the turbo had gradually come into full force. The power band has become more usable and the leaner to redline. As we explained to Don, we can make even more HP but if we chase the HP drivability becomes an issue. However, if we focus on drivability then the car naturally ends up with more HP.

The system received some back up help from various components. The car was fitted with new valves, rockers, guided and seals. We then cut the angle of the valve seat from 2 angles to 5 to promote better air movement through the heads. We did not add bigger ports nor polish the heads. We know that the max HP on a CIS is near 500HP and we can achieve this without big boost and without big valves. The bigger the valve and port, the more air in the head. The more air that comes in then has to move out and that means a delay in time in throttle response. So we always pay close attention to the type of head work we do and match it for the system. In Don’s case this was perfect. We added coated and X-rayed springs. The coatings help keep friction down on the springs. Less friction means less heat and less stress. We removed some weight from the valve train by using titanium retainers on the valves. We also twin plugged the heads for insurance. The main reason we do this is a follows: The typical CIS turbo car creates a spark far before the piston is ready to fire. The idea is that a fire wave starts and by the time it can make it to the other side of the piston for a near complete burn the entire combustion chamber is lit. The trick is when adding a higher CR and displacement you also create more heat and the chamber becomes less efficient than it was before. The placement of the factory plug is favored to one side. We drill and machine a second spark plug on the opposite side of the piston. This allows the piston to receive a complete burn without the risk of the fire wave. It takes less timing or advance spark to create the explosion in the chamber. By less timing we create the same HP and we reduce the stress on the main bearings, rods, rod bearings, and crank. It is a win/win situation.

[Aggie93]

Part 2

Grouped with the twin plug for added safety were some coatings. The coatings were of several types to serve several purposes. The piston cylinders received a thermal displacement coating. This allows the chamber to dissipate heat faster and more evenly to produce a cooler chamber. The pistons received a barrier of ceramic coating to the top and a dry lube coating to the skirts. The rods also received an oil shedding coating to reduce oil friction and drag. The head studs were replaced with like product. The car was built with many small details to ensure longevity and reliability. Even the ignition that was installed offers greater reliability. The system uses no moving parts and gets its reading from a digital signal. It in turn sends that signal to 6 coils that fire based on the order. The accuracy of this system is within a degree in timing. The coils fire harder and faster than a traditional CDI system. It also will not vary like the factory system. The factory system uses a brass gear on the distributor. The gear wears the timing wonders. The system installed also allows a sensor to take a reading in the intake of the manifold to reduce seven degrees of timing under boost. This is much of the same idea that Porsche used in the Carrera 2 Turbo. The clutch was also redone with a factory flywheel grouped with a pressure plate that is OEM then modified to our specs. We then take a spring center disc and reline one side with organic material and the other side is lined with Kevlar puck.

The result is a butter smooth clutch with a clamping force that can hold 500 RWHP without issue. We do not believe in using a lightweight clutch on a turbo motor. The motors carry low compression and the idea is that the momentum will keep things moving in the low end. When you hit the throttle then you already have help from the momentum on the clutch side. The result is a smoother, faster spooling lower end. After all turbos spool on load, not RPM.

We knew that the torsion bar system in Don’s car was tired and outdated so we went to work on updating it. In 1989 with the Carrera 4 system, Porsche adopted a coilover suspension system that was used from that point forward. Now all Porsches have coilover suspensions. We used the same on Don’s car. The system used was a RSR Bilstein setup that had raised spindles to allow the car to sit lower and retain proper steering geometry. The spring rates chosen were 300 pounds front, 400 pounds rear. The idea was to create a ride that was good for track and still would allow your teeth to remain intact driving to the video store. The stock sway bars were retained. The 86 forward 911 turbos had larger bars then previous models. By using this setup if Don feels down the road he needs to upgrade he can. Springs rates are changed very easily as well as ride height and bars. The goal is to keep the car usable in all areas. This setup allows that.

Moving the car forward is easy, stopping it is another issue often overlooked. The car was already upgraded with 18-inch turbo wheels so we took advantage of that. The rotors were upgraded to 13 inch and the front calipers painted red and moved to the rear. The fronts received new “big reds”. Adapters were used to accommodate the bolt pattern and the hat size. The original fronts were moved to the rear to keep the balance of the breaks. The big reds are capable of stopping 1900HP per axel. If you don’t have balance in the rear than stopping will actually become decreased. This setup allows an ideal setting and balance.

Now that we have addressed most of the performance standards we should visit a few other goodies that were changed. The GT tail on back was creating an unbalanced down force on the car. We knew we wanted to add an additional oil cooler. The frontal oil cooler is nearly 3 times the size of the original and will drop oil temperatures at least 25 degrees even on a 100 degree day. The added air ducts not only allow balance to the car, it provides air to the oil cooler as well as the breaks.

Don’s project was completed in about 4 months and encompassed the total engine overhaul, suspension, breaks and the paint on the front nose. The interior even had time to receive a few upgrades as well. The outcome was a 475+ HP car creating over 500ft lbs of torque at 3000 RPM. Able to tear most new turbos up at the Glen, yet starts and get groceries on the way home.

[rsrfan]

I remember reading that article when it came out and remember Don's posts on the car. You got yourself a great one for sure. I cannot remember how Stephen dealt with the fueling requirements but suspect he had the fuel head flowed. Short of an EFI conversion, about the only improvement I can see is a change out to twin scroll headers and a GT3582R...

[quattrorunner]

Yeah, thats pretty sweet. Nice car, I can only dream.
Stephan is still very helpful when it comes to these cars, spoke to him(texted) the other day, he helped me decide on an intercooler. He's a smart sucka.