The Numbers Tell the Story
by Scott Dalgleish
We now have the results of our Bobber’s engine modifications (February issue), which uses the Branch-O’Keefe 95-inch No. 4 kit. As you may recall, we decided to go for more than the “easy power” of simple bolt-on performance items, and instead selected the proven No. 4 package which includes ported heads from Jerry Branch of Branch Flowmetrics. (Since then the company has reorganized and is now called Branch-O’Keefe.)
As with most high-performance modifications, the initial 20 to 25 percent increase in power comes easily. The addition of a high-performance air filter (Arlen Ness Big Sucker in our case), larger cylinder displacement, flat-top pistons, and a free-flowing exhaust can be had for about $1,500 plus labor.
If you figure the stock horsepower to be in the neighborhood of 67, take the potential gain, divide that into the expense, and the answer is the approximate dollar cost per horsepower. In this example it is 1,500 divided by 16.75, which equals 89.5; you will expect to spend about $89.50 per horsepower.
The cost may be slightly higher for an EFI-equipped Harley because you will need to buy some form of “tuner” and, depending on your goal and which product you select, you will save cost in the long run because many offer the ability to provide tuning capabilities beyond air/fuel adjustments, including ignition timing and the ability to tune each cylinder as a stand-alone engine. These features will aid in future power enhancements if that is desired. For most riders, this first level will provide a great deal of satisfaction and reliability.
The next level of power enhancements takes a serious jump, not only in the percentage of power gained but also in the cost to achieve it. If the goal is 100 or more horsepower, it requires all the above as well as cams, forged pistons, and cylinder heads with porting, bigger valves and modified combustion chambers. The Branch version features a proprietary chamber modification.
It has been almost 20 years since Jerry Branch published his little orange book titled Harley-Davidson Evolution 1340 Performance Tests. Within its 52 pages, Branch documented the performance of a number of modifications to the then-new Evolution V-twin motor. All of the modifications were performed on a stock 80-cubic-inch motor. The goal was to get 100 horsepower at the rear wheel.
When you think about it, that is a tremendous achievement; because of the frictional losses that happen between the motor’s sprocket shaft and the tire’s contact with the ground (or dyno roller), the engine’s raw output needs to be around 120 horsepower out of 80 inches, which is 1.5 horsepower per cubic inch. This was all to be done on pump gas without nitrous, turbo or supercharger. By the end of the book, Branch had accomplished his goal, which required a big cam, Mikuni flat-slide carburetor, high-performance ignition, free-flowing mufflers, a lot of cylinder head reworking, and meticulous assembly and dyno tuning. For Branch’s trouble, he became a household name at Harley shops; his was the motor that became the V-twin hop-up standard.
Now let’s return to the present. Harley’s Twin Cam 88 motor replaced the Evolution powerplant on production bikes more than seven years ago. It has 88 cubic inches of displacement and comes equipped with either the 40mm CV carburetor or 44mm EFI (electronic fuel injection). This motor also has a couple of tricks and a few quirks between its cases; on the positive side, the displacement can be easily increased to 95 inches, and the crankcases are stronger; and on the negative side, the cylinder head’s ports are constricted, the cams are chain driven, and the base timing isn’t adjustable. The Twin Cam motor is bigger—95 inches is the norm and nobody does serious hop-up work to it without first increasing its displacement—and it has the potential to produce some big numbers.
The kit we used consisted of reworking our existing cylinder heads including bigger valves, porting, polishing, and the Branch proprietary combustion chamber; forged pistons made by JE for Branch to match his revised head design; cams made by Andrews for Branch with a 255-degree duration and a 0.560-inch lift for both intake and exhaust; gear cam drive with chrome moly pushrods; and all of the necessary bearings, gaskets and keepers. Branch offers this package, as an option, on an exchange basis that will get a quicker turnaround than using your own bike’s heads.
This combination has been toughly dyno tested and has all the bugs worked out for you. The only caveat is that you select an exhaust system that has been used in one of the many Branch dyno tests. Carburetor recommendations are available as well. EFI programs are available on the Power Commander Web site www.powercommander.com.
Since we didn’t use one of the exhaust systems previously tested—the SuperTrapp Road Legends X Pipe designed by Paul Yaffe—we needed to develop our own EFI map. Due to the striaght-pipe design, the X Pipe would not be our first choice for a performance exhaust system. We have documented many times the benefits of using a 2-into-1 exhaust system, which would yield much better numbers as well as make tuning easier. The BUB 2-into-2 Jug Huggers have also proven effective. However ineffective the X Pipe may be, it did make the desired statement in achieving the look we were after in our Bobber.
The dyno tuning was completed at County Line Cycles under Arman Gevorkian’s watchful eye, as well as yours truly. The results speak for themselves. Our Bobber’s numbers came in at 101.9 horsepower at 6,000 rpm and 99.9 pounds-feet of torque at 4,300 rpm, as measured at the rear wheel on a Dynojet dynamometer. This performance would undoubtedly be improved with an optimal exhaust system. The numbers tell the story: Branch knows his stuff.
The MSRP of our package is $1,849. Add the cost for the Ness Big Sucker air filter, a free-flowing exhaust system, the cost to bore the cylinders, and a Power Commander, and the price comes to about $3,000 plus labor. Using the same cost-per-horsepower formula we used in the beginning of this article, ($3,000 divided by 34) the cost comes to $88.20 per horsepower. That’s as cost-effective as the first 25 percent gain we discussed.
If you try to piece together your own kit selecting from the seemingly endless selection of aftermarket products available, your cost can skyrocket. And with the Branch-O’Keefe No. 4 kit, why bother? This kit offers excellent performance that may be the premier Best Buy of the Harley performance world. U
For further information contact Branch-O’Keefe, 562-597-2850; www.branch-okeefe.com; and County Line Cycles, 805-578-8830; www.countylinecycles.com.
|
