FEATURED IN HEAVY DUTY MAGAZINE (Issue #187)

Picking a cam is as easy or as hard as you want to make it.

I’ve been very happy with the performance of HDMAG, my Project M8 Super Glide, with its S&S Cycle 124 Big Bore kit and 540 cam. When the engine copped the 124 package, the 540 cam was a perfect match for me and my riding. Any bike making 120ft/lb from 2000 to 5000rpm is always going to be fun in the real world of daily riding. But now there’s a Road King Special that has joined the shed permanently. Packhorse will free up HDMAG to become more of a round-town hot rod with occasional trips to the dragstrip. With the change of riding focus, I decided that a change of cam to better match the rpm band was in order. It would be easy to change pistons to add compression, or have the heads ported and fitted with bigger valves for even more power but a simple cam change would move the power further to the right on a dyno sheet and that fitted in with my plans.

Picking a camshaft is easy. Or is it? The S&S Cycle 540C camshaft fitted when Super Glide’s engine grew from 107 to 124 was originally designed for heavier bikes, especially those clocking up touring miles, it was a good choice for my original plans. But then Road King happened, and the desire to make the Super Glide more of a hot rod with the occasional trip to the drag strip. Cam specs and recommendations were explored. There are almost as many options for M8s as there are bikes. Reading what other people have read, misunderstood and regurgitated was entertaining and in some cases downright scary. If you know nothing about engines, please don’t try and tell others what they should be doing. Cam recommendations that start with the words, ‘I heard …’ or ‘I thought …’ should be ignored.

After looking at lots of options and asking the advice of a couple of people I trust, I still wasn’t convinced on any single cam. There are several very good options from a variety of manufacturers, and I believe that many, if not most, of them are ground in the same facility in Illinois. That means that they’re all manufactured to extremely high tolerances. Where the variations come from are the designers. Each of them has their own ideas based on science, experience and in some cases – old fashioned gut feeling. There are aftermarket companies like S&S Cycle, Andrews, Comp Cams, Star Racing, Cycle Rama, and Feuling who have been grinding cams for decades.

Because I’m stubborn, following the herd and using the same cam as everyone else wasn’t an option. Besides, if I run the same parts I’ll get the same results and won’t learn as much. Where’s the fun in that? You learn by doing. My M8 Super Glide is a reasonably light Softail that never carries a pillion. What I wanted was a stronger top-end pull for occasional dragstrip passes but without losing too much of the awesome bottom-end and mid-range pull from the S&S 124 big bore. My search led me to eventually settle on the Star Racing F35A. The specs looked good. To confirm that choice, I sent a message to George Bryce – the owner of Star Racing and designer of Star Cams – and asked for his valued advice. His reply was to use their 3/4 Race cam, adding that it wouldn’t take too much away down low but would add 10hp up top. Also on my shopping list was one of their billet compensator ramps. They’re made for Star Racing by Liberty Gears, a company with a long history of manufacturing drag racing parts. The cam was in stock at Rollies Speed Shop but not the compensator so a credit card hit later, they were both on the way direct from Star. They’re not the cheapest options out there but they were my Christmas present to myself! I’d been discussing a cam change with Jim from Twin Tune Australia. When the Star 3/4 was announced as my choice, he was keen to see the results. It wasn’t one that he’d tried but was on his list.

My first M8 cam swap happened under Jim’s experienced eyes but only after we ran HDMAG up on the rolling ruler AKA the Dynojet 250i dyno, so that we knew what we started the day with. As this was my first time inside an M8 engine, it was a real learning experience. They’re a bit different to an Evo or a Shovelhead! With relatively new S&S lifters already fitted, they were re-used. As was everything else behind the cam cover other than the camshaft. With .585” of valve lift, stock valve springs aren’t going to work. Thankfully I already had a set of S&S Cycle valve springs fitted. Safe to .605”, they were good to go with the 3/4 Race cam. Tuning it was all Jim’s work. I’m smart enough to stay out of the road when professionals are busy. Late in the evening, it was declared finished and complete. The results of the 100% throttle, fourth gear runs are there for all to see. Yeah, it lost a bit under 2500rpm but I’m more than capable of changing gears to make things happen from slower speeds. On a trip along the M1 the next morning, 2500 works out at 110km/h and it pulls hard from that point in top gear and keeps pulling as hard as your licence can stand. Cruising between 2200 and 2500 in top gear, or in a lower gear through the 50km/h roundabouts of suburbia, Jim has made it smoother than a gravy sandwich. That’s also due in part to the basic design of the 3/4 Race cam. I’m very pleased with the results. As for George’s prediction of adding 10; he underestimated it. The horsepower is 13.89 higher at the peak but that’s not the whole story. Check the torque curves. Both cams are making 120ft/lb at 2500rpm with the 540C holding it to 5000 whereas the 3/4 Race carries it through to 5750. The graph shows numbers that are now higher but out in the real world, it pulls hard all the way to 6500, and then pulls hard again when you grab the next gear. I ask you; what’s not to like about that?

It’d be very easy to get carried away with HDMAG but it’s still a street bike. I already have a dragbike … and need to keep reminding myself of that fact. Repeatedly. Anyway, as I was saying. The next logical step is to add a Screamin’ Eagle 64mm throttle body and the matching 64mm cast intake manifold. I’ve just got off the phone from Mark at Harbour City Harley-Davidson and both of those parts are going in an Express Post pack this afternoon. Another hit to the Visa. The Screamin’ Eagle 55mm cast manifold currently fitted will migrate over to the Road King Packhorse. The new throttle body and manifold should add a bit more torque, especially further up in the rev range. But the dyno will measure the before and after. Then the dragstrip will confirm those improvements. Stay tuned.

- Mick Withers, HEAVY DUTY EDITOR