365 C/4 Page 2

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!