The combustion chamber on Harley V-twins has benefited from better gas flow characteristics with every evolution, but the standard porting is not best suited to high performance. Porting is a subject in itself, and will be dealt with in the near future by someone who knows what he’s talking about, but we have reached the point where you’re really not going to sit in a shed with a bastard file and an heirloom toolkit. If you’ve got a fully equipped workshop – and we are talking fully equipped here, with lathes, milling machines and a space heater – you’ll know much more than I do already, and I’m amazed you’re still here.
This is where the engineers come in, and you have to put yourself in their hands. Sure, you can buy heads etc and stick them on yourself, but when you’re that deep in, you’re not going to put those heads in without seriously considering what you want from the bike. Well, if you’ve got any sense you’re not.
You’re in big money country now and a half-cocked Stage Three will be not much better than an amateur Stage Two – certainly not worth the additional expense of the parts. Yes, I know you can get ported heads off the shelf, but ported for what? More torque or more horsepower? Higher or lower revs? Fuel efficiency or straight line ability? Before you start you need to know where the power is needed, and what sort of power, to determine the size and shape of the valves: until then it’s merely a technical exercise.
And it’s not just heads, and that is why we now start to differentiate between engineers and fitters. A Stage Three motor really should be a blueprinted engine. It’s no longer enough that it is as good as an assembly line can make it, if you’re going to do it properly, it’s got to be as accurate as the original drawings: the blueprints. If the drawing has a dimension of 1.7701mm that’s what it has got to be, not +/- .005mm. Production lines don’t do that, fitters can’t do that, mechanics would love the time to learn that. The only people who can do that properly are engineers – and even then, only the better engineers. The bad news is that there aren’t many left because there are few coming up through the ranks, and that’s because production lines have rendered a lot of basic skills obsolete and machine minders fill their steel-toecapped boots in industry.
A blueprinted engine will be less stressed than a production line example – even a good production line example – because everything will work as it should: as it was designed to do. The sort of engineer who will be capable of matching the specification will be more than capable of sorting out your porting, cam and carb requirements to make it better than the blueprint for your specific application, and that is the ultimate state of tune for your bike. Harley-Davidson produce motorcycles for the masses, an engineer will make a motorcycle for you … assuming you know what you want, and can communicate that to your chosen professional.
With thanks to Andy Hornsby of American-V magazine from which parts of this article have reproduced . Originally published 22/1/2004 © American-V magazine