Metric Thunder News

Cobra's Quick Fix: Honda VTX1800F

WITH 110 CUBIC INCHES OF V-TWIN KABOOM pushing it, Honda's VTX1800F moves down the road quite smartly, thank you.

As originally appeared in Cycle World

But you know how we motorcyclists are when it comes to performance: Enough is... well, never enough.

We always yearn for more - especially if getting it involves reasonable expense, easy installation and immediate results. So, when we decided to give our test VTX-F a bit more urge, we took a route that promised to deliver those easy, immediate results. We swapped the stock exhaust for one that breathes a little more freely, and coerced the fuel-injection system into being more generous with its distribution of dead dinosaurs.

Fortunately, we were able to obtain the equipment needed for both tasks from the same source: Cobra Engineering. At the time, Cobra was the only company selling an aftermarket exhaust for the F-model VTX: the drag-style Speedsters ($579), which feature full-length heat shields and a cleverly hidden crossover that connects the two pipes right at the front of the straight sections.

We also snagged one of Cobra's Fi2000 Digital Fuel Processors ($200) (discounted at Metric Thunder) to juice up the Honda's EFI.

Installation of these pieces was straightforward and absent any surprises. The entire stock system came off as a unit in less than five minutes, and bolting up the Speedsters required just short of a half-hour - much of which was spent fiddling with the hose clamps that hold the heat shields in place.

Installing the Fi2000 Digital Fuel Processor is another no-brainer that most people should be able to accomplish in minutes. It involves velcroing the unit to the top of the EFI black box under the seat, and connecting four wires using the provided Scotchlok connectors.

We were pleasantly surprised at the results. Stock, the F-model churned out 83.5 horsepower at 5100 rpm and 97.0 foot-pounds of torque at 3700. The pipe and Fi2000 bumped those numbers up to 88.6 hp at 4900 and 104.7 ft.-lb. at 3400 - increases of 6 and 8 percent, respectively. From idle to around 2700 rpm, the torque curve didn't change much; in fact, between 2000 and 2700, it was a foot-pound or three lower. Despite that, throttle response right off idle was noticeably more crisp, and the torque increase from 2700 up to redline was significantly greater than stock. Indeed, at around 4100 rpm, the torque output was almost 9 ft.-lb. higher.

We perceived the biggest improvement when rolling the throttle open at 3000 rpm and above, and when running up through the gears wide-open. In those circumstances, the VTX accelerated noticeably harder and was much more willing to rev. And because both the horsepower and torque peaks occurred at slightly lower rpm, that added performance was more easily accessible.

Credit much of this improvement to the crossover in the exhaust system. Without it, the Speedsters would likely have behaved like most other straight pipes and poked a sizable hole in the powerband, probably in that 2000-to-2700-rpm range. But the crossover gives each cylinder's exhaust pulses access to the total volume of both pipes broadening the system's effective tuning range. So, it allows the pipes to be tuned for higher-rpm performance without greatly penalizing the low-end and midrange. Plus, the resonant changes brought about by the crossover give the VTX-F a deeper, more pleasing exhaust note than the VTX1800N we tested in our December 2004, issue, which was fitted with non-crossover Cobra drag pipes.

Some of those performance improvements also result from the more-efficient fuel mixture provided by the Fi2000. When checked with an exhaust-gas analyzer, the modified VTX maintained a near-ideal air-fuel ratio of between 14.2:1 to 14.5:1 all the way through the rpm range, whereas in stock form, it was much leaner at low and mid rpm. Cobra's Fi2000 Digital Fuel Processor incorporates three richening screws under its flip-up lid, but the mixture was perfectly dialed-in as delivered, so we never had to touch them.

For just over $750, then, practically anyone can bump the performance of their VTX1800F enough to get rewarding results. All they need are a few basic tools and a burning desire for more kaboom.

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September 2, 2005 03:47 PM