365 GTC/4 Background The front-engined Ferrari 365GTC/4 was introduced to the world at the 1971 Geneva Auto Salon as the replacement of the 356 GT 2+2. The C/4, as it is commonly known, had a distinctive wedge-profiled body designed and built by Pininfarina in Turin. The C/4 body was comprised of welded steel panels and aluminum trunk and hood over a steel frame. The car was in production for 18 months with a production of a mere 500 cars.
The car was powered with a Columbo-based, 4390 cc, 60 degree V-12 engine rated at 320 bhp (DIN) at 7,000 rpm and 318 lb-ft of torque at 4,000 rpm. The engine has an 81mm bore and 71 mm stroke and runs at an 8.8:1 compression ratio. The 4-cam motor is similar to that of the 365GTB/4 Daytona except that it uses a wet-sump lubrication system and fed through 6 side-draft Weber carburetors (38-DCOE-59/60). The wet-sump system utilizes an oil gear-pump sharing its housing with twin water pumps at the front of the engine. The pumps are chain-driven off the crankshaft. Twin oil-filters are mounted in the in the center of the vee. The carburetors are connected to the cylinders through inlet ports positioned between the inlet and exhaust camshafts in order to reduce the height of the engine for fitment under the low-profile hood. Euro-spec C/4s had a single Marelli distributor mounted in the rear of the engine and driven off the right exhaust camshaft. US-spec cars were equipped with dual Marelli distributors on each bank. The engine configuration gives the C/4 engine a beautiful and stately appearance both under the hood and when on an engine stand.
365 GTC/4 Project Car
This
Ferrari 365 GTC/4 has been modified by CAROBU Engineering LLC. The modifications include a 5.0 litre C/4-412i hybrid engine, Brembo GT “Big Brake” kit, 17” “Speedline-style” wheels and height adjustable suspension. As the resale prices show, the C/4 is a “sleeper”
Ferrari whose image was outshined by the popular “Daytona.” However, the elegant Pininfarina styling, and the steady road manners of the car made it an excellent basis for modification.
C/4 – 412i Hybrid Engine - The goal of this project was to increase the power and torque of the engine while retaining the balanced character and stock appearance of the C/4. In order to accomplish this, it was elected to install the 5.0 liter engine from the later 412i. The 412i engine is based on the same Columbo block and made an excellent basis for the C/4 project. In stock form, the 82mm bore and 78 mm stroke results in a 4942 cc displacement operating at a 9.6:1 compression. The higher compression of the 412 was possible through the use of Bosch K-Jetronic fuel injection. The 412 engine was rated at 340 hp at 6000 rpm in the original configuration. For this project, the stock carburetors and air boxes were retained.
Heads and Camshaft - In order to design and build a high performance street engine fitting for the grand touring nature of the C/4, CAROBU elected to use its proprietary “hot-street-grind” camshaft, used successfully in the 365 GTB Daytona project car, to control the engine breathing. The lift and duration of the intake and exhaust lobes are the same measuring 0.363” maximum lift and 247 degrees of duration at 0.050”. The camshaft grind provides good torque and power without the drivability issues associated with more radical grinds such as the “P6” race-grind.
To properly utilize the additional lift and duration provided by the CAROBU camshaft, the intake and exhaust ports were massaged to match the port flows with the camshaft. Computer simulation modeling was used in order to determine the ideal intake and exhaust flow profiles. Figure 1 illustrates the head flow, in cfm at 28” of water, of the intake and exhaust ports for the original 412i heads and for the “ported” 412i heads. The original heads flowed 127.2 cfm at 0.350” valve lift. After porting, the intake port flowed 144.7 cfm, and increase of 17.5 cfm or 13.8% increase over stock. As mentioned above, in order to reduce the height of the engine, the intake port positioned between the intake and exhaust cams and manifold configuration of the C/4 is less than ideal for engine breathing. For comparison, the 365 GTB/4 Daytona project engine, with a more advantageous intake port design, had an intake port flow at 0.350” lift of 168.4 cfm at 28” of water. The exhaust ports of the heads were not ported as the computer simulation predicted that additional exhaust port flow would actually hurt the performance of the engine. The exhaust port flowed 127.9 cfm at 28” of water.
Induction and Ignition System - Since the K-Jetronic Bosch injection of the 412i would not be adequate for the modifications of the project engine, and to keep with the original character of the C/4, it was decided to keep the 38 DCOE side-draft Weber carburetors, fitted with larger 32 mm venturis. This required some modification of the 412i heads to accommodate the C/4 intake manifolds including plugging the injection ports in the heads. It was also necessary to modify the heads to accommodate the C/4 distributor drives. A Black Stallion solid state electronic ignition kit with programmable ignition timing was fitted. This kit includes a special stock-appearing distributor with Hall-sensor trigger, ignition coil, wiring harness, spark plug wires and a programmable ignition module. The kit allows for a reliable ignition upgrade while retaining a completely OEM-look. Some of the features of the ignition include extreme accuracy in ignition firing, live ignition curve adjustment, in-car switching between two preprogrammed curves, and “soft” engagement rev limiter. With these modifications, the engine has actually become a 365GTC/4 – 412i hybrid.
Short Block - The 82mm bore and 78 mm stroke of the 412i engine was retained resulting in a 4942 cc displacement. Based on the engine simulation modeling, it was decided to increase the compression ratio to 10:1. This would provide increased power and allow for the use of premium pump gas. The engine was equipped with Razzo Rosso forged aluminum pistons. The stock connecting rods were replaced with steel Carrillo rods. The stock
Ferrari crankshaft was retained.
Headers and Exhaust - Due to the additional power produced by this engine, computer modeling predicted that the stock
Ferrari exhaust header with 35mm OD primaries was inadequate for the job, especially since the inside diameter of the exhaust port is 1.45” (36.8mm). CAROBU previously demonstrated in the 308 project engine that port matching the exhaust header and port increased engine power. CAROBU Engineering designed and fabricated a new, larger tube, stainless steel header with 1.625” (41.2mm) OD primaries. Again, in order to preserve the character of the original header, the 6-2 design using flat 3-1 collectors was retained. These collectors were custom made by Burns Stainless LLC. The headers were ceramic coated in order to minimize under hood temperature and to match the original black exhaust paint. These headers are available from CAROBU for the C/4.
The car was also fitted with a Tubi Style under-car stainless steel exhaust , also ceramic coated to match the original parts. It is interesting to note that this particular car was equipped with a modified exhaust system installed by others. The system eliminated the center muffler/resonators. The muffler/resonator in the OE system and the Tubi system also provide additional exhaust tuning resulting in a broader power band for the engine. Testing of both systems would be done as part of this project. Further discussion of exhaust testing will follow.
Dynamometer Testing - Upon completion of the engine build, the engine was tested on the CAROBU Engineering DTS dynamometer in order to break in the engine, tune the carburetors and set the optimum ignition timing and to test the engine performance. Running the engine on an engine dyno is also helpful in that small issues such as oil, and water-leaks can be located and corrected while the engine is out of the car. The CAROBU dyno facility was also designed with the capability of running the complete under car exhaust system to insure proper tuning. Following break-in and tuning, this engine produced maximum power of 410 bhp at 6,400 rpm and maximum torque of an amazing 385 lb-ft at 4,500 rpm. This engine makes 90% of maximum Torque by 3,800 rpm. No one can say that this
Ferrari lacks low-end Torque! By comparison, the original C/4 engine, dyno tested in the “as-received” condition, made 291 bhp at 5,300 rpm and 300 lb-ft at 4,900 rpm.
As mentioned earlier, this car was fitted with a non original, custom, stainless steel exhaust system. The original
Ferrari exhaust, and the Tubi-Style system include a center resonator section that “connect” the front three cylinder with the rear three cylinder exhaust on each side of the motor. This provides a secondary tuning effect providing for a broader power band and increased horsepower and torque. The custom system deleted the center resonators, thus isolating the exhaust. Both systems were tested on the dyno. The Tubi system made nearly 5 bhp more maximum power and 8 more lb-ft of maximum torque. But what is really evident is the improvement in mid-range torque. At 4,100 rpm, the Tubi system produced nearly 45 more lb-ft of torque!
Additional Powertrain Modifications - The additional power of the engine required improved cooling. To increase the cooling capacity, an aluminum radiator was installed. The thermal conductivity of aluminum is almost double that of brass, greatly increasing the ability of the radiator to reject heat.
This is a direct replacement aluminum radiator, 100% TIG welded with multi-louvered fins and billet machined fittings. The aluminum radiator also saves 35 pounds due to the lightweight aluminum construction. To improve the responsiveness, the engine was also fitted with a custom lightweight aluminum flywheel mated to a modified Kevlar-lined clutch to take the extra power.
Suspension and Brake Modifications - The guiding design principle at CAROBU Engineering is to design modifications that keep with the original character and intent of the automobile and to make a “balanced” car. In keeping with this principle, CAROBU chooses to use high performance parts from
Ferrari OE suppliers such as Koni and Brembo or from special suppliers such as Tubi that build special exhausts for
Ferrari racing and special construction cars. To design a “balanced” car, CAROBU prefers to make improvements in the three aspects of performance - Engine, Handling and Braking.
The engine modifications have been discussed above. In order to address the handling of the C/4, CAROBU upgraded the shocks and wheel/tire combination. CAROBU Engineering in consultation with the owner chose to convert the OEM Koni shocks to height-adjustable shocks. This conversion allowed us to lower the ride height of the car and adjust the spring rates. The stock Konis have adjustable rebound settings allowing for suspension tuning.
The conversion utilizes 2.5” diameter racing springs that are available in a variety of spring rates. By choosing the proper spring rate and shock-valving combination for the desired ride-height, the handling of the car could be optimized. Since this car was to be used primarily as a street car, moderate spring rates of 300 lb/in front and 200 lb/in rear rates were used. The car was lowered approximately 1” from stock. The stock shock-valving was retained.
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Gruß,
Lamberko
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