Cams for the pipes you probably already have
Most Harley Twin Cams are fitted with some sort of “stage 1” kit fairly early in their life. Many of these involve the use of the currently fashionable drag race style exhausts. At this level, most of these can be made to run quite well with correct tuning. However, when more power is required, any of the upgrades invariably involve the installation of different camshafts.
Camshafts are a major player in the power characteristics of an engine, and are also heavily influenced by the exhaust system. It’s not just about the total lift, but about the points at which the valves open and close, and the rate at which this happens. One of the many aspects of cam design is overlap, which is when both the inlet and exhaust valves are open at the same time. The idea here, is to allow a low pressure wave from the exhaust to help draw in more air from the intake, which increases cylinder fill, and therefore torque. The downside of this, though, is that there is always a high pressure wave travelling back up the exhaust, and open pipes (drag pipes), or those similarly styled pipes with minimal baffling, can’t reduce it. This reverse pressure wave causes flow reversion, and the air that we are trying to get into the engine is either stalled, or pushed back out. This varies with rpm, and also to some extent, with throttle position, and the end result is a combination that may produce a high peak power number, but can have a horrible dip in the power curve, normally in an area where a Harley is most often ridden. Whilst we can be very creative tuning with fuel injection, we can’t change the laws of physics…
The stock cams, which are designed around emissions constraints, don’t have any overlap, so these issues, caused by the interaction between the exhaust and the cams, are minimised. Flat spots, and deceleration popping, can often be dialled out by correct tuning.
Unfortunately, the stock cams don’t produce much power, and the true, streetable, high performance builds, where we want power everywhere, require a suitable exhaust system. These true performance exhausts, which also tend to be much quieter as well, aren’t cheap, especially if something else has already been purchased. In any case, the “cosmetic” pipes are very popular.
So, if the pipes are handcuffed to the bike, but more power is required in the area that the bike is most often ridden, but without the adverse side effects, or breaking the bank….
…enter the new Wyrd Brothers XH-66 camshafts. Rather than design a set of cams and build the rest of the components around them, reverse engineer them, and design them to work with the exhaust system that is already fitted. These XH-66 cams are designed specifically for the stock compression, fuel injected, Twin Cam 96 and 103, with open exhausts. They also build early torque on the FLs with slip on mufflers, which retain the restrictive header pipes with the catalytic converter. I haven’t tested them yet with a really good exhaust, but have a sneaking suspicion the torque curve will be rather exceptional.
They do not require any headwork, different valve springs, adjustable pushrods, or compression releases, and are amongst the quietest running cams I’ve yet experienced. As with all camshaft changes, the inner cam bearings and lifters must be changed for long term reliability.