Written by Moore Good Ink
Last month, in the February News Brief, engine builder Norm Beerhorst of Ultra Tech Racing Engines, Mishawaka, Indiana, discussed the following:
• The advantage of the pressurized engine—centrifugally supercharged or turbocharged
• Heat and its consequences
• Preparing for the HOT ROD Drag Week™
• Testing valve train with a Spintron
In this March issue Norm tackles two further issues:
On the differences of the induction and combustion processes between the turbocharger and the naturally aspirated engine
With pressurized engines you can achieve a more controlled combustion compared with the complexities of trying to manage reversion and detonation within the narrow RPM band of a maximum-effort naturally aspirated engine. Of course having access to the correct fuel ingredients can be helpful. Nonetheless, normally aspirated engines encounter reversion and pulsing and other complications. The column of air entering the cylinder is severely disrupted when the valve closes. Consequently, it bounces off the back of the valve head as it’s moving at full speed and then collides with the next incoming charge. Unavoidably, the engine is efficient only in a narrow rpm band
In contrast everything in the induction tract of the boosted engine is under pressure. There is almost no reversion. As soon as the valve opens the mixture is pushed into the cylinder, the valve shuts, and the mixture is ignited. It burns smoothly and the spent gases are expelled completely from the cylinder, aided by the next incoming charge during valve overlap.
In conclusion, with the naturally aspirated engine, it is crucial to find the rpm band where it runs best. The pressurized engine, on the other hand, presents much less chaos and as a result the engine’s sweet spot delivers a much wider power band and at much lower engine speeds.
On camshaft selection
You can use a much milder camshaft on a pressurized engine than you could with a maximum-effort normally aspirated engine. Air flow and cylinder heads and intake manifolds are still important on the maximum-effort pressurized/boosted engine, but the shape of the cam lobes can be less radical when 3,000-plus miles are a must without part failure.
Ultra Tech Racing Engines
417 S. Byrkit Street,
Tel: (574) 256-9462