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Prepping Porsche Heads for 24 Hours of Racing, Dana Johnson
By Dana Johnson
One of the more interesting jobs I’ve had in my shop recently was a thoroughbred racing Porsche GT3 prepared by one of my regulars, Jerry Pellagrino of European Performance Engineering. Of course it was just the heads, but it was still very exciting. Jerry brought me two of these water-cooled three-cylinder four-valve heads. The heads were off his factory-built Porsche Super Cup race machine.
Besides having a Porsche GT3 Super Cup car, which costs a mere $115,000 and races in an international class of similar cars, EPE also has a GT3RS. The RS is a purebred race machine that fetches about $250,000 per copy. No wonder Jerry didn’t flinch at $5,000 worth of new valves!
Over the years, Porsche 911 heads have changed but the configuration has always remained the same. These engines are opposed flat-sixes with individual air-cooled or water-cooled heads, like many motorcycle heads. Although they are similar, the work to rebuild them is not. Some heads only need a basic valve job and guide replacement, while others require a full port job and the installation of a second spark plug hole. As was mentioned in last November’s issue (See page 49, "Get Your Motor Runnin"), a second spark plug enables fuel to ignite from both sides of the combustion chamber.
According to Jerry, few Porsche teams are allowed to open the motors to do any work because the factory likes to keep close tabs on most of these engines. However, because of EPE’s long history with Porsche, Jerry was given permission to open them up. Once inside, let me tell you, these heads were a "thing of beauty." They were factory CNC ported and had flat shallow chambers.
When starting to work on these heads – especially with this being a new job and all – I used great caution disassembling, measuring and recording all of the valve stem protrusions. And except for some valve guide wear, the heads were in good condition. The Super Cup car was near the end of its service limit so Jerry wanted to go ahead and do a complete valve job. The only problem was that after placing a call to Porsche Motorsports, we discovered guides were not available. And to further aggravate the problem, Porsche said you don’t replace the guides you replace the whole head!
With factory replacements out of the question, and not wanting to make Jerry buy new heads, I went with my next best option. When I have valve guide availability problems, I go to my trusty SI Industries catalog. They have an excellent catalog that includes a valve and guide listing with all their dimensions as well. In searching for the Porsche’s dimensions (6 mm), I found several with the correct I.D. I decided to choose the one with the slightly larger O.D. because it was the closest match I could find. And just to be certain of my selection, I called Lee Tagliamonti at SI who assured me that the guides I chose would be suitable for my application.
After the guides arrived, my biggest concern was with how to turn the O.D. to keep it concentric and taper free. I decided to consult with Ted Phillips of DCM Services and he was a great help. Ted made me a very precise mandrel to set up the guides for O.D. machining. After turning the O.D.’s, the seal end and port side taper were the finish work. When I made the guides, I was able to make them longer and add a taper, which didn’t really affect the flow of the heads. I wanted to make the guides as long as possible to eliminate any valve rock. The original guides looked to have been installed before the CNC work was done and therefore were cut off with very little taper. It may have added a little flow but the integrity of the valve was my main concern.
The old guides were core drilled and driven out cold with no problems. I made a cup-shaped tool to install the new guides. Then I put the tool on a 6 mm guide-drift and it fit the seal step perfectly. I pushed the guide in until the cup bottomed out on the spring seat, leaving the guide at the proper protrusion. Making special tools can be time consuming, but I know it will be time well spent because we will be doing more jobs like this one in the future.
It was obvious that the special mandrel Phillips made was worth it when we machined the valve seats. After I installed the guides, the seat run-out was better than .003˝. This made the seat machining and stem height correction much less work than I anticipated. The assembly of the heads went smooth, and the car ran great!
Afterwards Jerry invited me to his shop to see the cars and the completed engines. Both of the engines are 3.6Ls but the Cup car puts out 385 hp and the full race version RS pumps out 425 hp. Some of the differences in the GT3RS are larger titanium valves (approximately $200 apiece to replace), carbon fiber bodywork, individual butterfly induction system, exotic electronics including a complete data acquisition system and a flat bottom belly pan (for more efficient aerodynamics).
But these extras don’t come cheap, as the RS is nearly twice the price of the GT3 Super Cup car. Both of these cars are built in limited numbers and buyers must meet strict qualifications (one being a big bank account). These cars require a strict maintenance schedule, which includes a complete engine teardown every 30 hours. And, as you might imagine, the parts that are available from Porsche Motorsports are not cheap. At the time of my visit to EPE’s shop, the GT3RS was being prepped to compete in this year’s Rolex Daytona 24-hour race.
I should also mention that the GT3RS had only 16 hours on the motor before the race and therefore it didn’t need guides or springs in my opinion. But I installed new retainers and valves, just to be safe. You don’t want to take any chances in a 24-hour race. It’s far less expensive to pay for the maintenance now than to break during the race.
By the way, the No. 99 NETTS Racing Porsche GT3RS finished a respectable 29th overall, and 12th in class.
Dana Johnson owns Import Machine Services in Framingham, MA. He has been rebuilding VW and Porsche engines since the 1960s. firstname.lastname@example.org