74 IROC RSR replica

Big motored street and track machine Updated 10/8/09

You might get the sense that we like cubic capacity in our 911s, and this project is another example. The plan? A big tyred, 3.6L powered, lightweight IROC replica. Modern injection for everyday reliability, but with the punch to keep up with almost anything on the road. Sound like fun? We think so!

At left is the project start - an 82 SC. The highpoints - a rare pair of Sonjay custom 16x10" rear Fuchs, and steel widebody conversion. The negatives? we were soon to find out!
After a bit of poking around it became clear that this car was covered in filler. almost 6mm thick over the entire rear guards. A few rust bubbles were evident too, so it was no choice but back to metal. Some poor repair work was also evident, which would have to be fixed without slathering on the filler! Many hours were spent massaging the rear guards back to shape without resorting to filler.
Following the shaping the bare metal was coated in POR15 paint. POR almost guarantees that rust will never be a problem again, as it actually uses any moisture to cure and form an impenetrable seal. The rear lid catch panel also required a lot of straightening too. While you can't see it here, it's the same story on the other side of the car. Thankfully with the POR on we could see the shape was pretty good - minimal final filler will be required.
The car had the later G50 style flares, which was no good for the desired IROC look. The G50 panel was modified to resemble the early torsion bar access hole and welded into place.
Primer time - this is Tiecoat primer, specifically designed to bond to POR15 paint and existing painted surfaces.
With the exterior coming along, it was time to attack and repair the common rust areas. The front tank support was bad. Here it is cut out and the insides coated in POR15. A repair panel was fabricated from thicker material with an internal reinforcing brace to allow the car to be jacked from here in the future. At this time we also cut out the metal in front of the support to fabricate an RSR style oil cooler duct.
Here's the duct in place. It allows airflow through a front mount cooler and under the car, and replicates what the factory did on 74 RSR race cars. You can also see the new support panel welded in place. The mounts are made for one of our Setrab coolers for plenty of cooling.
Here,s a shot of the oil cooler duct from inside the front trunk, where you can clearly see the new panel work. This mod isn't strictly neccessary for a front mount cooler, but ensures maximum efficiency and is definitely the right way to do it!
The front trunk area painted. The tank was flushed and cleaned and painted in an OEM style epoxy. I can say it's worth pulling out your tank drain plug from time to time and cleaning the filter. The big battery is not going to stay - a lightweight one will replace it. We also spent a lot of time cleaning up the wiring loom. The air control duct work won't be going back in - we have a custom setup for heat and cold air that weighs next to nothing and is a breeze to operate compared to the confusing Porsche controls!
Fibreglass bodywork saves a ton of weight compared to steel. This is our fibreglass turbo guards and and IROC front bumper. That's a fibreglass hood also in place. The guards weigh about 4kgs each, versus 14kgs per steel piece. The front bumper saves over 25kgs versus the standard bumper and valance.
Here's the rear IROC bumper in place prior to paint. You can also see that the tub has been coated in the first coast of Mexico Blue - our chosen colour! In this shot it's been colour sanded ready for following final coats.
And here are the final coats on the tub. The sunroof hole is still in place, but will be filled with a custom removable lightweight fibreglass insert. That saves about 15kgs too, right from the top of the car where you don't want the weight.
Another mod we chose on this car was a through bonnet fuel filler, but rather than a centre fill which is awkward to use and kills any luggage space, we went for a side mount flush filler.
Here's the filler in place. It's a billet filler from a motorcycle, and I think it makes for a nice custom touch.
The current exhaust is also unique. We use the factory 3.6 heat exchangers, coupled with a stainless dual pass muffler. This muffler is lightweight and fits in really nice where the cat might normally live. The centre outlet will have twin pipes - GT3 style. Again, a lot of weight was saved with this exhaust system, and the straight through design should be good for power.
A shot of the car with all panels now in Mexico Blue. Looking sweet, but still a lot of work to do. Rubber gaskets will eventually go between the bumpers and guards etc for a more factory appearance and durability.
This is a mod I've wanted to do for a while. It's a raised centre tunnel to move the 915 shifter to a much more ergonomic position. The centre tunnel will now more resemble a 964 model car, with a short shifter that doesn't require a stretch to first when you're strapped in tight.
Here's the tunnel welded in place. The shift rod was shortened for the new position, which places the shifter about 100mm up and back from stock. The standard handbrake with new linkage still fits behind it, and there's a spot for a custom extinguisher mount too. All of the standard tar sound deadening mat has been removed, and the metal coated in grey POR15 for anti rust protection.
The interior rework continues. These are custom aluminium dash fascia panels, which eliminate the air controls and side vents. The dash is getting trimmed in suede, with a late model larger centre vent fitted for better airflow. The aluminium panels will be trimmed in vinyl. The one hole is for a flush mounted CD player. As a street car a radio is an accepted compromise :-) Some sound deadening mat has also been fitted over the dash metal to stop any annoying vibrations. We're allowing a total of 20kgs of sound deadening in the car to make it nice on the street. I think we'll still be under 1100kgs when finished, maybe even close to 1000. With 3.6 power it should be a rocket! :-)
The engine bay has now been painted, and is waiting the installation of the 3.6 and gearbox.
Front suspension is now re-installed. The steering rack has been cleaned up and checked, and new turbo tie-rods installed. A Carrera sway bar is doing duty, and 21mm torsion bars are in place. With the front end of this car being all fibreglass, bigger than a 21mm t-bar would really hurt the street-ability. A arm bushes are now nolathane, and all parts have been cleaned up and where appropriate coated in POR15.
Front brakes are AP 4 piston calipers over carrera 24mm thick rotors. Braided brake lines are in place. As this car features the turbo width IROC guards, 1" spacers are used to position the front 8" fuchs correctly.

Next to come - clean up of the 3.6 engine and reinstallation of it and the rear suspension..
Rear Suspension features new wheel bearings, 28mm Torsion Bars, and poly springplate bushes. Rear brakes are stock 911SC. Rear sway will be a carrera item, with Bilstein Sport shocks.
A mini project was to clean up the intake manifold of the 3.6. A number of sensors have been relocated to the rear of the manifold to clean up the plumbing and wiring. The main wiring loom has also been moved to the rear where it will be largely out of sight. The vacuum signal for the power brakes has also been simplified to a single feed from the left plenum. The factory airbox was cut apart to form a solid mounting flange for the standard bell mouth. Air filter options ( if any ) have yet to be determined. A custom bracket now supports the AFM in place of the airbox. I'm confident this will make for a much cleaner looking top half of the motor..
Valves adjusted, distributors serviced, and everything cleaned up like new and the engine long block is almost ready to be re-installed. The fan and valve covers are now Mexico Blue for aesthetic appeal.
It's time for some interior finishing work. the custom fibreglass cover for the raised shift tunnel has been trimmed in black carpet to match the rest of the carpet set. We've even managed to incorporate a small change tray - how civilised! The handbrake linkage for the raised mechanism was quite a challenge, particularly considering it had to fit around the shift rod and still actuate the standard handbrake cables. A lever system was fabricated that is doing the job, although at a 2:1 ratio the handbrake must be kept adjusted properly for best operation. Factory rubber gearshift and handbrake boots are in place.
The dash has been retrimmed in black alcantara, complete with mexico blue boot stitching around the instrument cluster. That's a late (88+) centre vent in an enlarged dash opening for more air with our custom heat and air control system. We can supply these vents now too, and can also arrange the re-trim in alcantara of your dash (about $800 for a dash retrim). The fabricated aluminium dash panels are covered in factory vinyl, and that's a steering wheel quick release in place.
The engine bay has come up nicely, with the work on relocating sensors and intake manifold clean up really making a difference. New fuel lines have gone throughout the car, and wiring has been moderately revised and cleaned up and relocated.
Even the coils have been colour coded Mexico Blue, as has the fan and valve covers. New plastics and rubber make this engine bay look like a new one. The factory airbox has had the bellmouth cut from it for a no-nonsense air intake system. No filter for the time being, but that may change with a pod in the future.
Factory exhaust manifolds have been sand blasted and high temp painted, and all new gaskets etc fitted. These team with our custom side mounted muffler and twin centre outlet exhaust. The engine has been thoroughly cleaned and detailed. The Bilstein sports are in place, as is a Carrera rear sway bar in new bushes.
And a ducktail now lives at the rear, proving to be much lighter than the IROC wing. This is one of our import ducktails - reasonable quality given the price. Email us for more info. Note the lack of weight at the rear of the car with the lightweight exhaust system and removal of factory brackets.
Remember the carbon rear reflector idea? Here it is executed. A lightweight carbon panel replaces the factory reflector. A sticker was used as a mask, and then the panel sprayed in blue. The sticker is removed to reveal the carbon letters, and then the panel is clearcoated. Even though this is a 74 replica, a bit of this century performance doesn't go astray..
The interior is complete. The combination of suede dash, door tops, and headliner work well. Stainless Carrera script sill plates are just some of the details here. A Prototipo lives on the steering quick release, which has been colour coded blue. Mexico Blue Recaro logos on the seat mounts are the final touch. Note the 935 style mirror on the drivers side glass. Small, not very effective, but cool.
The engine bay is designed to be clean and functional. An anodized blue catch can is now mounted in the inner right corner, with a blue breather hose from the oil tank. Importantly every component has been cleaned up like new or replaced, making servicing much friendlier.
The finished article. Here at 911 Parts we are really pleased with the outcome - it matches the original vision of so long ago. Alignment has been completed, and with camber plates and the aggressive ride height we have achieved 3 degrees negative front camber and 2.5 rear.
Despite this being a street car that is track friendly, our first drive was on track at Wakefield Park. With corner balancing yet to be completed, we managed to lap in the 1:09's - a strong testament to how well the car will perform with some more sorting, and 12th outright of 50 odd cars in the PCNSW event.
There are always details to be finished, and mods. Note here there are no exhaust tips. A new muffler will soon be fitted as the current system is too quiet! For the most part though this car is going to do some miles on the street and track.
In the shakedown session on track a few things were learned. no.1 was how important corner balancing is - with mismatched diagonals handling was different right to left and front brake lock-ups were all too easy. No doubt the light front end also contributes to easy front brake locking - some bias adjustment may help to add some more rear brake.
The other key learning was decent power and low weight is still our favoured recipe for big fun and a quick car. We'll be at Oran Park in late August for some more fun :-)