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Kostecki Engine Centre test the CHI 3V heads against iron 4V units.

Base Engine Specifications

To make the contest as fair as possible, the base engine specs in the comparison were kept as similar as possible. The 3V engine features some serious hardware and is set up to suit circle track racing on a strict premium unleaded diet. A King 3.75-inch stroke crankshaft was selected along with King 6.20-inch stroke H-beam rods. Custom Diamond pistons give a streetable10.58:1 compression ratio, given the alloy heads. A mechanical roller camshaft was used with 245 degrees duration at 50-thou, .680-inch lift at the valve and a 112.5-degree lobe separation angle. 1.75:1 Jesel rockers were used for the ultimate in accuracy and reliability. Adding to valve timing accuracy are the bronzed lined lifter bores. The block has priority oiling to the main bearings and is fed by a Petersen external pump.

The 3V cylinder heads are delivered to KEC by CHI as bare castings - bare in the truest form of the word, they do not even have holes for the spark plugs! KEC have developed a complete CNC programmer for the CHI head that machines them in their entirety - inside and out. This enables KEC to machine the ports and combustion chambers exactly in relation to each cylinder bore. When the CNC mill has finished, the valve spring bases are milled to the right angle, the pushrod holes are drilled, the sparkplug holes are bored and tapped, the combustion chambers are ported to absolutely identical volumes and the intake and exhaust runners are fully ported.

A Weiand X-cellerator manifold was fitted with port tongues (these were designed and custom cast in aluminium by KEC) to match the port shape in the cylinder heads. The entire intake manifold was Jet Hot coated to insulate it from the heat of the oil in the valley. Up top a Da Vinci carburetor, modified by KEC was chosen. This uses a 930 cfm base plate and a 750 cfm centre section. All jetting and air bleed and emulsion tube tuning was optimised while the engine was on dyno.

The 4V engine uses exactly the same carburetor as the 3V, an unmodified X-cellerator manifold and has a 9.5:1 compression to tolerate premium unleaded with iron heads.

When the heads come off the CNC mill, they have 220 cc intake ports with a minimum cross sectional area of 2.36 square inches. Valve sizes are 2.150-inch and 1.60-inch. The valve seats are cut with a five-angle tool (32/45/55/60/75-degree) that is used for V8 Super car cylinder heads. The combination of angles is critical to maximise both low and high lift flow figures. On the flow bench the CHI 3V flows 335 cfm from its 220 cc port and 2.150 valves at 28-inches of water.

The mighty 4V heads have also been ported and are fitted with larger 2.19-inch valves. Their monstrous 275 cc intake ports flow 355 cfm. Although the 4Vs flow more air in absolute terms, the ports are much larger than the 3V's. The object of the dyno testing will be to determine which port shape, size and cross-sectional area will be best suited to the stroke and bore combination of the Cleveland.

Dyno Testing

The dyno results tell a drastic story. The big 4V heads made power all the way to 6800 rpm but peaked at 6400 rpm with 408hp. Torque peaked at 5900 rpm with 353 lbs/ft. When the CHI-headed engine hit the dyno, things stepped up a notch or two! Peak power jumped to 530 hp at 6700 rpm, which is a massive 122 hp improvement over the 4V's.

The real story, though, lies in the torque curve where, even at 2900 rpm, torque is up by a massive 122 lbs/ft. The fat torque curve continues all the way to its peak at 5400 rpm of 468 lbs/ft. Peak torque has improved by 115 lbs/ft but it is the average torque across the entire rev range that leaves the 4V stumbling in its wake. The 3V produces more torque at 2900rpm than the 4V does at its peak.

On the street or on the drag strip, the 3V would be many car lengths ahead of the 4V. This is not to say that 4Vs are not capable of producing remarkable power. At the test and tune of the 27th March, KEC's own G/Gas Mustang ran an 8.60, a tenth of a second off the National record, with a set of 4v heads and a single carburetor. For the majority of street and strip cars, the 3Vs will deliver a more responsive, harder hitting engine than the 4 Vs. The moral of the story is that cylinder heads must be properly matched to the rest of the engine and that a big fat torque curve will stomp all over a glossy peak power pony on the drag strip.

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A bullet-proof bottom is the best insurance for tough engines

CNC ported 3Vs are awesome performers.

On Dyno, the 3V produced more torque at 2900 RPM than the 4V did at its peak!

Click here to view dyno graph

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