Engineering the Formula Fit

  • 17-Dec-2009 09:30 EST
FFDemoRacecar.jpg
Honda inaugurated its new support for grassroots amateur racing by designing a racing conversion for its 1.5-L L15A7 Fit engine to power cars in the class now called Formula F. (Honda Performance Development)

As might be expected, the cast-iron overhead valve 1.6-L Ford Kent engine that has been the foundation of Formula Ford racing in the U.S. for more than 40 years has long since gone out of production, leaving racers with few replacement parts.

In recent years, aftermarket replacements have been made legal by the Sports Car Club of America (SCCA), but the parts shortage and limited production of aftermarket components caused costs to escalate to levels out of line with the entry-level position of the Formula Ford (FF) class.

“Today, a nationally competitive Formula Ford engine costs $13,000,” noted Sandy Shamlian, owner of Quicksilver RacEngines, a leading Formula Ford engine builder.

The solution was a new engine. But there were several significant obstacles to permitting a new engine in the class, beginning with the compact size of the old Ford engine. The Honda Fit subcompact car employs a similarly tiny engine, a single-overhead cam 1.5-L engine that was sufficiently compact that engineers at Honda Performance Development Inc. (HPD), the company’s U.S. racing division, thought it could be a good candidate to replace the hoary Kent motor.

As the plan progressed, HPD Production Division Manager Marc Sours tasked Quicksilver with some preliminary research, which included Shamlian getting a Fit engine from a junkyard and test-fitting it in the engine bay of a Swift DB-1 borrowed from racer Todd Bardwell. Once he saw that the engine mounted easily in the space, the Swift was shipped to HPD, where they began the process of turning a production car engine into a race engine.

The first order of business was to bolt the engine into place, so they made the necessary engine mounting brackets. A more significant issue arising from the change from Ford to Honda power is the difference in the bolt pattern where the engine mates to the transmission.

The notion of designing a new Hewland gearbox housing with the Honda bolt pattern was floated, but the aim of the project was to develop a purely bolt-in conversion kit that would permit converted cars to be switched back to Ford power subsequently. So the team opted to use an adapter plate sandwiched between the engine and the gearbox, with a longer input shaft to accommodate the increased distance between the two. 

This approach was complicated by the fact that the bolt patterns of the two engines were nearly identical, with bolt holes about half a diameter from lining up. That meant that the mounting bolts in an adapter plate would interfere with one another, so Honda tilted the engine 10 degrees to offset the holes. That move had the benefit of helping slightly lower the center of gravity.

With the engine bolted securely in place, “there were a lot of packaging challenges,” recalled project leader Tom Grosart. The Swift DB-1 was selected as the prototype for installation of the engine because it is one of the most prolific designs in American FF racing, and because it was designed with extreme emphasis on reduction of aerodynamic drag.

That means the engine bay is the most crowded and unforgiving of any FF chassis, so if Honda could make the Fit engine work in it, it would work in the others. The areas of particular interest were the intake tract, the exhaust, the oil system, and cooling.

In the Swift chassis the dry sump pan mounts as a stressed member, and the Kent engine had the oil pump and filter attached externally. To clean up the engine bay and simplify the system, the Honda design retains the Fit’s regular internal oil pressure pump and engine-mounted oil filter.

In a bit of elegant engineering, the scavenge pump was built as a cassette device that slides into a dedicated spot in the dry sump casting, which features internal oil passages to the pressure pump and filter, eliminating all the external oil plumbing except for the lines to and from the oil tank, which is cast integral to Swift’s transmission bellhousing.

One reason for the internal oil pump was the desire to retain the original Swift radiator, whose inlet and outlet did not line up well with the attachments on the Honda engine, and having a belt-driven oil pump would have fouled the coolant lines.

HPD engineers have designed an intake manifold casting that wraps close to the engine’s head in an effort to minimize interference with bodywork. The HPD team was frustrated that the circuitous prototype exhaust header seemed counter to the Swift’s engineering simplicity, so they have simplified the production item, eliminating some turns, said Grosart.

The finished package weighed 7 lb (3.2 kg) more than the Kent engine, but the prototype oil pan was milled from billet, so the cast production part will significantly reduce its mass, Grosart said. The team is getting its first production parts in at this writing and will follow up with an SCCA-supervised test of an engine outfitted with the production pieces to ensure its power will mirror that of the existing Ford Kent engine.

On the dynamometer, the prototype engine was tuned so that “line for line, it was the same power curve,” remarked Grosart.

They did this using a combination of an inlet restrictor and engine mapping to duplicate the Kent’s power output as closely as possible. Still, the Honda demonstrates a bit more low-end power, while the Ford has a little more at redline because it isn’t choked by a restrictor, he said.

The earliest Fit engine kits for the Swift are scheduled to ship to customers in February, and the engine becomes SCCA-legal April 1, with a price for the complete conversion kit of $11,750. This will include fuel injection and a Denso alternator, which represent notable advances over the Kent’s Weber carburetor and total-loss electric system. Subsequent replacement engines will cost $2500, making a converted Swift much cheaper to operate over time.

The Honda engines, with their modern components and assembly practices, are expected to be more consistent and durable than the Fords, dramatically reducing the need for continuing maintenance and regular rebuilds.

Honda will develop and sell conversion kits for the Swift DB-6, Citation, Van Diemen, and Piper chassis, giving owners of nearly all currently competitive chassis the opportunity to switch engines. In recognition of the two eligible engines, the SCCA has shortened the class name to “Formula F,” which can stand for either “Ford” or “Fit.”

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