Aermacchi 175 Chimera

The original Two Brothers Racing RC31 (NT650 Hawk)

(anyone have any better pics of this bike?)

Two Brothers Racing

The story of the RC31 would terminate here without the intervention of three year old North American road race team TBR, comprised of brothers Kevin and Craig Erion with their tuners Mike Velasco and Dan Kyle. In 1989 TBR selected the NT650 Hawk GT as their racing platform.

“Nobody had raced the Hawk,” said Erion. “We missed the first two races of the season developing the bike and, to the total surprise of all, we entered and won the remaining five races, taking the 1989 GP2 class championship.” In 1990, TBR moved up to campaign in the open-class Pro Twins GP1 series, finishing 3rd overall for the season. “We took that bike from 39 rear-wheel horsepower in stock trim to over 70 horsepower (probably 85hp) in race trim,” said Erion. “We were competitive and we began to get noticed.”

In 1991, TBR traveled to Japan to compete in the All Twins Battle and they caught the attention of HRC Director Mr. Oguma, who invited them to visit Honda RD to meet the NT650’s designers and discuss ways to increase power. “A designer at Honda RD, Mr.

Hasumi, became interested in our work,” said Erion. “His team was designing the CBR600F2 for ‘91, and Honda wanted to field an F2 race team.” For 1991, TBR had a Honda contract to race the F2 in Supersport and the RC30 in Superbike, thus beginning a relationship with Honda that would flower and bear fruit for many years to come. While TBR had moved on from the RC31 platform, other teams had followed suit and were tasting victory with the RaceHawk. ( ( (

T.B.R. RC31 Race specification.

The basic concept ot the RC31 race engine was Velasco’s, based upon his years of work at Honda Racing. The heads were ported by a respected Canadian, Rick Tomacic, and according to Erion, flow better than factory VFR heads. The RC31’s heads were fitted with 1mm oversize Del West titanium valves, which weigh only 60 percent as much as steel valves. Light titaniurn valves continue to follow a cam contour long after steel valves would have floated.

Velasco selected a Megacycle cam, based on what had worked in VT500 Ascots. Three-milimeter-oversize Wiseco domed pistons (82mm) were installed, increasing the displacement to 700cc with a compression ratio of 12:1. Con rods were cut from titanium billet by Crowers really big, and 60 to 70 grams lighter than stock, says Erion.

The downdraft intake system was topped by two 39mm racing CV carburators taken from an RC30 race kit. Ignition came from a Honda RS750 dirt-tracker, providing 36 degrees advance by about 3000 rpm for optimum performance with higher compression. The new ignition system extended the rev limit to 12,000 RPM and eliminated the requirement for a battery. The Exhaust system dimentions were copied straight from the RS750.

Kerker fabricated the two-into-one exhaust pipe in stainless, feeding an RS-style canister and muffler section.

Engine longevity was increased by the installation of an RC30 radiator and another sourced from a VFR750. Coolant from the bottom radiator was pumped to both cylinders in parallel, eliminating the issue of rear cylinder overheat experienced with O.E.M. sequential routing.

A complete road-race front end was lent by Honda, taken from a ex-Joey Dunlop Isle of Man TT1 bike. Twin 323mm disk brakes, machined-from-solid calipers with Nisin pads, delivered more than double the original stopping power. A Fox shock controled the rear suspension.

The 17-inch rims were 3.5/4.5-inch, shod with bias-ply front/radail rear mchelin 250 GP slicks.

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