In November 2009, we purchased a nice looking but neglected 1974 911 (G Series). It's a car I have dreamed of owning since I first saw one zoom by me on the New York State Thruway way back when. The engine needed a top end rebuild due to worn valve guides and most of the parts were pretty well worn out and the tub had some rust. In the process of deciding what to do with the car, we decided to make a fun track day car out of our new addition to the garage.
In this blog, I will recap the build process to convert an early 1974 911 to a 1974 IROC RSR (like the one Mark Donahue won the 1974 IROC series with but adding a few 21st century mechanical improvements). My job was to figure out what parts we needed and purchase/coordinate all of the procurement. I started with Bruce Anderson's book to get an idea of what to do. I never built any sort of car before.
More pictures can be viewed in the project gallery: http://www.p101tv.com/view-album/78/1974-porsche-iroc-rsr
The general idea of the build goes like this:
- Hot rod the engine but still stay with 2.7L, we don't want to weaken the mag case by over machining
- fix the known issues with the engine (head studs and the timing chain tensioners)
- get the car to shift better
- new shocks and stiffen the suspension
- strip out the interior and add safety equipment
- add the body conversion parts
- new wheels - some idiot curbed the Fuchs and one rim is bent
Before embarking on a project of this sort, it is almost essential to have welding as a core skill. This will save a ton of time and money. This is a no expense spared re-do.
The odometer read 23K miles on it (just 5 positions on the clock for this car). So we were guessing it was broken but it was still turning. We used Franz Blam Racing (FBR) as our engine build shop. When the case was cracked open, much to everyone's surprize the engine had never been rebuilt before. So we figure the car has 123K miles on it. This was a lucky situation since the car came with no maintenance history. On the other hand, the car was a ticking time bomb with the original timing chain and tensioners.
It probably is no news to anyone who has gotten into a Porsche 911 engine rebuild, but plan to spend 20-25K (USD) for a quality rebuild. A little luck, but the original motor and a 7R case were part of the project car. This was figured out during the pre-purchase inspection by looking at the number on the vertical surface of the fan housing support. The race shop sent the case for machining out in California, Glen Thompson I think. The case was also shuffle pinned (no boat tailing). We salvaged the cylinders and had them replated (Nikasil). I purchased JE 10.5:1 pistons, Pauter lightweight rods and ARP rod bolts as the engine basis. The cams were redone by Web Cams. They weld on new material and then grind the cams to the desired profile. The lower valve covers had already been upgraded to the aluminum 930 covers. They were machined for 6 more spark plugs for the twin plugging. I bought new upper aluminum covers from Hargett to replace the original magnesium covers. FBR cleaned and refurbished all of the reuseable parts to like new condition. We also changed out the oil feeder tubes and added a Carerra Oil pump. The stock pump will not move enough oil. This engine needs a hotter ignition, so we twin plugged and added an Electromotive ignition. We ripped out all of the CIS emissions and the stock airbox. It was replaced by 46 MM PMO carburators (modern day Webers). The nose bearing was worn out and replaced. The original motor mounts and tranny mounts were replaced with Wevo semi-solid mounts. There is a Mallory replacement fuel pump. The fuel pump and oil system is now under the front bonnet. We also added a fuel cell. The case has Dilavar inserts and fresh head studs and the engine is completely reassembled now.
The Drive Train
First order was to add an LSD. I was fortunate to find one on EBay from an abandoned project (Guard Transmission LSD). The next issue was to figure out what to do with the original transmission. It was in good working order but most of the gears would need to change because our new motor build is putting out about the same power as a 3.0 Liter. We sold the original transmission on EBay and bought a 1979 915 gear box. This also means we had to change out the transaxles and spindles, also found on EBay. The specifics of the change is the 1974 has 4 bolts on the transaxle and the 1979 has 6 bolts. The 1979 transmission was completely rebuilt and a taller 5th gear was added (27/24). The clutch was replaced with a Stage 2 racing clutch from Kennedy Engineering. With the new transmission and clutch change, the clutch cable has to be replaced with one having a hooked end. To address the shifting, we replaced the stock shifter with a Rennshift shifter and we changed the linkage and added a Stomski Racing coupler. The car shifts as well as a 997.
The stock oil cooler is inadequate in this build. I wanted an off the shelf oil cooler so I did not have to wait weeks to get a replacement. I went with a Setrab racing oil cooler from Patrick Motorsports. They also have a nice oil temp light that fits into the dash where the clock used to sit. The oil lines were removed from under the car. There is a new high volume oil canister (18 qt capacity) and hydraulic lines and AN fittings. The oil lines run through the passenger compartment on the passenger side floor. A custom elbow is required to snake the oil line though the headers. There are two oil filters one on the exit and one before the return to the tank.
Headers and Mufflers
How to get into this to meet the noise limits we have on some of the tracks and not spend an arm and leg on stainless steel? After spending a bunch of time, we went with European Racing Headers and SuperTrapps. The headers were sent for ceramic coating inside and out to reduce the heat on the bottom of the case and to help fend off corrosion.
I wanted a one stop shop to get all the parts for the suspension. We needed heavier everything. I found a set of spring plates on EBay and we refreshed the spring plate covers. The rest of the suspension was designed by Clint Smith at Rebel S Racing Products. It can take a while to get your parts but everything Clint provides is first class. We started with a set of RSR struts. They were a customer return and we made a great deal on them. They have 1.5 degrees of negative camber. We decided to go with Eibach coil overs. The fronts are 400 with a 220# helper spring. In the back we are at 550# (I think). We added new sway bars in the front and back. Our old front sway bar did not go through the body. With the new through-body sway bar, we will need to add some reinforcement before driving real hard. On the 1974 911, the rear sway bar was optional and our car did not have it, so we added the welded in supports and a rear bar. I cannot tell you the sizes of the ARB's. One day I will put a caliper on the bars and record the info. Our 1974 came with aluminum trailing arms. These were cleaned, inspected and reused. We also added monoballs and new bearings. I found a set of turbo tie rods and the ball joints were replaced with the bump steer kit from Clint. We are running 9 and 11's for tires right now with plans to go wider, so we added the tire rub kit.
It quickly became clear the stock brakes would not be able to last more than one or two track laps. Upgrading to 930 brakes is a popular but ever more expensive option due to the rarity of the parts. Clint suggested we go with fitting Boxster brakes. Clint makes a kit to fit the early 986 calipers onto the car. He also helped to find the rear adapter kit. The calipers were purchased from a salvage yard. We did not hook up ABS. Hawk pads fit perfectly. The master cylinder has to be upgraded to the 23 mm master cylinder to get proper pedal pressure, part number is P916132 from Automotion. We are still experimenting with rotors. The first set is already cracking after one easy day of track driving when we broke in the motor (Zimmerman cross drilled-high performance...expensive and not lasting). We are going to try out Carrera slotted rotors from Paul at Weston Motorsports in Tampa, Florida.
I found a set of wheels which are replica Speedline wheels. They are heavy and do not have the look we are going for but, they will work for break in and as rims for rain tires. The plan is to have one piece wheels made out of the original Fuchs.
The interior was cleared out except for the dash and the instruments. A set of FIA rated Sparco EVO seats are installed with Schroth Profi II harnesses, a classic Momo Prototipo wheel was added. The pedal cluster was rebuilt. A full roll cage was custom welded and installed. A 17 inch Longacre convex rear view mirror has been added. The Electromotive ignition panel is mounted on the rear firewall. Fire system currently consists of a halon extinguisher mounted between the seats but will be updated to an automatic, three compartment system before racing. The instruments were updated to have an Autometer Comp II tach with shift light, oil pressure lamp.
We bought an IROC RSR fiberglass kit from GT Racing. The kit consists of front fenders, 14 inch rear flares, front and rear bumpers. The ugly US 5 mph bumpers were removed. The kit requires some expertise in fiberglass work to mount tabs on the bumpers for mounts and to fit the rear flares. Once the pieces were fitted, the car was sprayed in our garage with a two part primer. The car was then wet sanded to a smooth surface. The car was sprayed in the garage with orange paint from Summit Racing. Not a Porsche paint but our garage was not a place to do a technical paint job and this is a track car.
Ready for transport to have motor and drive train reunited with the freshened roller:
Documenting the Car
We purchased a log book from the Rennshift website to record all of the part numbers and details for when we need to fix anything. This is very important because we have so many non-stock parts on the car.
We were fortunate to be able to break in the new build on a beautiful fall day at Sebring, just 13 months after buying the car. Not one issue. So taking our time and buying quality parts has paid off.
Car makes its Inaugural Debut ....
Glowing in the Sebring sun: Dec 10, 2010
More to come.... TRACK TIME!
After just 3 track days, the Zimmerman high performance cross drilled front rotors have cracked. We are trying out some different Carrera rotors (slotted/not drilled). Paul at Weston Motorsports does our brake setups for both cars.
The fuel cell had a problem during the season opener AutoX event at the Bank Atlantic Center. The feed line in the tank became dislodged and it was not actually in the gas, but curled upwards (Jazz fuel cell). Looking into this more. Not a good situation that sloshing gas will curl up the feed line.
24 Hours of Sebring - 2011
It was an exciting weekend for the RSR. We ran the Solo 1 event. We placed in the middle of the field. It is clear this is a track car. With the PMOs rather than fuel injection, it was interesting to manage the throttle to keep good power through out the course. The highlight of the weekend were the comments from the paddock. The car received high marks for 'period correctness'. Many of the racers who came by to look at the car commented about their experiences with Franz Blam building cars for them back in the late 1970's for the 12 Hours of Sebring and the 24 Hours of Daytona.
Next Track Days: Feb 26 and 27, 2011 at Sebring
Story to follow...