Custom Chrome Revtech High-Performance Kit

CUSTOM CHROME REVTECH HIGH-PERFORMANCE KIT

CW EVALUATION

Bolt-on horsepower for Milwaukee's finest

FOR SOME, HARLEY-DAVIDSON'S EVOLUtion Big Twin offers the perfect combination of performance and reliability. Others see it merely as a starting point for greater things.

Custom Chrome Inc. (16100 Jacqueline Court, Morgan Hill, CA 95037; 800/729-3332) aims to capitalize on that latter philosophy with its RevTech High-Performance Kit. The company caught Cycle World's attention with ads claiming that the kit would produce 92 rear-wheel horsepower when installed on a stock 80-cubic-inch Harley-Davidson V-Twin. CCI also said that the $2700 kit could be installed by anyone with average mechanical skills using basic garage tools.

To test those claims, we bolted a CCI kit onto a 1990 Sturgis. The same kit is designed to fit any Harley-Davidson FXR model (except FXRT and FXRD) from 1984 through 1992, and FXST, FXSTC or FXSTS models from 1986 through 1992. The kit consists mostly of parts either made by or packaged under the RevTech name (Custom Chrome’s own brand of high-performance hardware), and includes dualplug, high-compression cylinder heads; an Accelerator 2 carburetor with extra jets; a high-lift camshaft with shims and adjustable pushrods; and a single-fire ignition system with a high-output coil and new plug wires. Also included is a 2-into-l SuperTrapp exhaust system, along with Custom Chrome’s Premium top-end gasket kit and Dyna Kote internal exhaust coating.

Rev Tech’s cast-aluminum heads are the centerpiece of the kit. They have a rough outer finish compared to the stock components, but utilize intake ports shaped for improved flow and better combustion. There’s also greater fin area to provide better cooling. The heads come with stainless-steel valves already in place; the intakes are .100-inch larger than the Stockers, while the exhausts retain the stock diameter.

Installing the kit involved more work than we had been led to believe. Custom Chrome does acknowledge that before the new heads can be installed, the pistons must be machined for proper valve-to-piston clearance. The kit includes a template for machining the pistons, along with brief instructions for cutting the valve pockets yourself. We strongly recommend, however, taking the pistons to a qualified machinist.

Besides, the template just gets you in the ballpark. After the pistons are machined, the actual piston-to-valve clearance must be checked by placing modeling clay in the valve cutouts, assembling the top end and rotating the engine through one complete cycle. In our case, a second round of machining and clay checking was necessary to provide the required clearances.

More machining was needed to install the cam. The area surrounding the inner cam bearing only allows clearance for the relatively low-lift stock cam; we had to use an air grinder to cut away enough of the crankcase to provide clearance for the high-lift, longduration RevTech 40 camshaft. For most people an air grinder doesn’t qualify as a common home workshop tool.

While the piston machining and cam clearance grinding are mentioned in the instructions for those components, several other items are dealt with either superficially or not at all. The RevTech intake manifold, for instance, would not fit into the vee of the cylinders until after .040-inch of material had been removed from both ends-a requirement not mentioned in the instructions and one that called for yet another trip to the machine shop.

Then there was the RevTech ignition system, which is claimed to offer easier starts, a smoother idle, increased gas mileage and prolonged sparkplug life. It may do all those things, but it also eliminates the stock rev limiter and causes the tachometer to read at half-speed. An adaptor for the tachometer is available but is not included in the kit. What’s more, the RevTech coil is slightly larger than the stock unit and, on our Sturgis, would not allow the cosmetic sidecover to be refitted.

Further uncertainties revolve around the ignition timing. The instructions state that the stock, 3 5-degree BTDC setting is only a “rule of thumb,” and recommend adjusting the timing “to suit your riding style.” Unfortunately, there is no mention of how to translate any riding style into a timing specification. Also, the Harley engine has only one timing mark, for its stock setting, and the kit doesn’t explain how to determine any other timing points.

We dynoed the RevTech-equipped engine with ignition timing set at the recommended 35 degrees and it produced 77 rear-wheel horsepower at 6000 rpm-up significantly from the stock 43 horsepower, but a far cry from the 92 claimed by CCI. Using a degree wheel, we played with the timing and got the highest reading, 80.1, with the timing set at 31 degrees BTDC.

Not long after we got the engine together and running, the rear cylinder head sprouted a serious oil leak that we eventually traced to a rockerbox bolt hole that had been drilled too deeply. The people at Custom Chrome claim they’ve never seen such a problem, but said they would replace the head for anyone who might experience a similar problem. To expedite our evaluation, we simply plugged the leak with a high-quality epoxy.

The leak certainly didn’t affect the bike’s performance. At the dragstrip, the RevTeched Sturgis hammered through the quarter-mile in 12.31 seconds at 1 10 mph-a major improvement over the Stocker’s best run of 14.28 at 92 mph. We might have been able to improve the performance of our RevTech-equipped Sturgis by adding to the 13 plates we installed in the SuperTrapp silencer and making the necessary jetting changes, but the exhaust note was already approaching an unreasonably loud level.

This boost in performance does come at a price, though. Due primarily to its radical cam, the RevTech engine doesn’t have the typical low-rpm snap of a Big Twin, which makes it slightly less enjoyable for aroundtown cruising. The reward is that once the tach hits about 3500 rpm, the bike really comes alive.

So in the end, the RevTech kit is a success, but with a few qualifications. For one thing, most people who aren’t already familiar with Harley engines are likely to have some problems with the instructions. In many cases, information is sketchy and doesn’t adequately link the separate components together. In others, it alludes to some complicated procedures without any explanation.

Most importantly, our RevTech engine did not make 92 rear-wheel horsepower. Custom Chrome insists it is withdrawing that claim from its advertising; nevertheless, the master instructions still contend that the kit is capable of producing at least 90 horsepower. Maybe, with unlimited dyno time and additional tuning, that figure is attainable; but with the resources available to most riders, our numbers are more reasonable expectations.

Even so, an 86-percent power increase-without benefit of turbocharging, supercharging or nitrous oxide-is mighty impressive. □