1. The Surbo, mechanically an air spindle, spins air into a compressive vortex which effectively raises air compression per throttle travel. At half throttle, the engine will reach the rpm red line, where the fuel cut-off will occur for most fuel-injection engines. If the rev limiter is removed, the revs can be extended by stepping further on the accelerator. For carbureted cars, there is no such limit so the revs can be extended straightaway.
2. At the original red line, since only half throttle is used, this means that a large part of the engine vacuum is still unused, and this can still be used to pull air into the engine, thereby extending rpm if there is no rpm limiter.
Examples of rpm-delimited Surbo-equipped manual cars are:
a. 2006 model Toyota Vios 1.5, which reached 95 kph in first gear.
b. 1993 Honda Civic VTi 1.6, which achieved 100 kph in first gear without having the accelerator floored. The original top speed in first gear was 80 kph at 8500 rpm.
c. 2008 Honda Accord Euro R, which exceeded 120 kph before full throttle in first gear.
As the original tachometers were used, we could only estimate the rpm achieved. For case a, that could be around 10000 rpm, with its VVTi engine having good top end power. For case b, around 11000 rpm. For case c, we actually saw on its aftermarket computer a record of 13000 rpm for 233 kph in 6th gear (throttle not floored yet), meaning at least 13000 rpm was achievable for this engine.
As a counterpoint, a Honda Civic ESi 1.6, the rpm limit of which was normally 7500 rpm, when delimited and fitted with Surbo, could reach 9000 rpm. This engine had a SOHC 16 valve head, and the Surbo gave it the "lift" of a DOHC 16 valve engine (original state of the VTi, case b).
This means that the Surbo has the effect of a higher lift cam, bringing each cam level to the next stage. In this case, it made SOHC like DOHC, VVTi somewhat higher than DOHC, DOHC maybe like Type R, and Type R nearer to a track car. The Surbo, with its air drawing power, fills up the void in the cylinders at higher rpm when the cam changes profile and widens the valve openings, avoiding the gasping for air and curtailing of power that can result if the air intake is not as optimized as the cam system.
Contact us if you wish to extend the revving capability of your manual car at a low cost!
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