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POSTED ON October 30, 2017

This 383 cube Cleveland hit the dyno and produced over 560 hp on pump petrol.

The engine was built by A1 Hi Performance, in Myaree, using readily available parts and some good old-fashioned know-how. The owner of this mighty mill asked only three things of the engine: to produce 500 hp, to rev to a maximum of 6500 rpm and to run on BP98 fuel. An engine such as this would deliver mid 11-second quarter mile times and be very safe and solid on the street. As Leon from A1 Hi Performance put it, with a smile, “You have to be careful what you ask for as you just might get it!” In this case the customer got an extra 60 hp and the potential to run mid 10-second passes.

After running the engine in using Superflow’s automatic break-in procedure, Geoff from C&R Motorsport, in Walliston, was able to give the engine its first full load dyno test. The results (shown in Figure 1) show the typical flat torque curve of a stroker Cleveland and a smooth power curve which peaks at 548.9 hp at 6050 rpm. Maximum torque is 486 lbs/ft at 5300 rpm but the engine is producing nearly 450 lbs/ft under 4000 rpm, which it holds until the 6050 rpm cut off point.

A quick glance at the oxygen sensor revealed that the engine was a little on the lean side so the Demon carburettor was jetted up both front and back in gradual increments over several more dyno pulls. The extra fuel made its presence felt mainly in the low to mid range rpm bracket where the torque figure was up 15 lbs/ft by 4300 rpm.

Figure 1 Figure 2

Figure 2 compares the engine’s sensitivity to operating temperature. Sometimes engines can produce significant power gains at a particular coolant temperature “sweet spot”. In this case the engine was tested at both 155 degrees F and 180 degrees F and showed no significant sensitivity to operating temperature. These tests were conducted with BP98 fuel and showed that even at a relatively high 10.8:1 compression ratio; the engine still produced strong power with no signs of detonation. This is exactly what is required from a street engine on pump fuel. The Clevo’s best power on BP98 was 560.5 hp at 6400 rpm and 491.7 lbs/ft of torque at 5400 rpm.

No performance engine dyno test would be truly complete without an injection of VP Racing fuel, just to see what gains could be made. In this case, it appeared that the camshaft overlap was helping the engine’s tolerance of detonation on pump fuel by bleeding off some cylinder pressure at low rpm. Nonetheless, a brew of VP103 was supplied to the carby and the engine was run up again.


Figure 3

Despite the fact that the engine did not really require the higher octane rating of the fuel, the burn rate and latent energy characteristics of the VP Racing fuel showed their worth with instant improvements in power and torque throughout the rev range. These gains were made with no jetting or timing changes. Figure 3 shows that peak power jumped to 568.7 hp at 6350 rpm and maximum torque cracked the 500 lbs/ft barrier with 502.1 at 5400 rpm.

Another glance at the air/fuel ratio revealed that the engine was still too lean and required more jetting. Unfortunately, no larger jets were on hand and time was up for the dyno day.

However, the main purpose of this motor is to run hard in street trim and the testing proved that the engine was safe at this power level on pump fuel.
But extra dyno time dedicated to further timing, jetting and spacer plate changes would undoubtedly result in more hidden power. Leon and Geoff are confident that over 580 hp would be achievable on the VP103 fuel. With 560 hp on tap and a big, fat torque curve, this thumper will be one of the toughest Clevos on the street.


Engine: 383 CID Cleveland.
Block: Standard, bored 30-thou.
Cylinder Heads: CHI 3V alloy with 185 cc runners, ported by H.I.T.
Crankshaft: Eagle cast steel 3.75-inch stroke.
Rods: Eagle H-beam.
Pistons: CP custom forged.
Compression Ratio: 10.8:1
Camshaft: A1 Custom solid roller.
Intake Manifold: CHI single plane.
Carburettor: Demon 775 cfm.
Ignition: MSD with custom A1 MSD wires.
Extractors: Pacemaker ceramic coated 4V four-into-one.
Exhaust: Magnaflow 3.5-inch mufflers fitted on dyno.
Fuel Type: BP98 and VP103.



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