Anything goes. Turbos, blowers, nitrous, strokers, billet motors, massive motors built for the purpose from parts that have never seen Auntie Janet’s bar and shield logo.
Quite bizarrely, a Stage Three bike would be the better bike in the vast majority of cases, and when compared to some of the bikes that drop into the Stage Four category, is likely to be quicker for longer in road use because there’s no guarantee that it’ll be hand assembled to the same standard as a Stage Three. That said, you could always get a Stage Four engine and get it blueprinted it to make it better still – unless you’re 100% certain of the ability of the original builder and you’d be foolish not to entrust to an engineer who you did trust implicitly.
It doesn’t get any more sensible when you consider that it is perfectly possible to bolt an off-the-shelf turbocharger to a stock motor, in which case it’s a Stage Four instantly. Stock cams and stock carb (on at least one option) with just the turbo’s plenum and convoluted plumbing to drive the compressor replacing the air-filter and exhaust. The only thing it has in common with the more serious hardware is the power output, which can be twice that of the stock motor: torque and horsepower. Oh yes, and cost. Stage Four doesn’t come cheap.
A turbo can work out at £3,500, and an engine can cost twice that before you open it up and fettle it some more – and it would be a strange horsepower junkie who could leave the cylinder head in place once they’d unpacked the motor … or the barrels.
And it’s worth a quick look at the crank while we’re down that far.
And it’d be silly not to weigh the pistons seeing as they’re out.
And is that a slight lip on the inlet tract … ? Pass me the emery …
Stage Four is the domain of the serious power addicts. Doubling the stock horsepower isn’t a challenge any more, trebling it would be good though. You won’t see many of these bikes on the road because they’ll have sacrificed a lot of their rideability along the way – in fact some will be physically unrideable – but on a quarter mile strip of tarmac, head-to head with someone who thinks they know better, they will demonstrate just how much you can get out of an air-cooled v-twin motorcycle.
The sad truth, though, is that yesterday’s Stage Four will be thrashed by tomorrow’s Stage Two, and the day after’s Stage One. Performance is transient, even in Harley circles.
There’s something you need to know: no matter what you’ve got it’ll never be enough.
There is some irony in that a lot of people are discovering Harleys today after years of buying faster and faster sportsbikes in search of the thrill they remember when they first started riding … only to discover that riding was more about freedom than speed, which maybe explains the sheer number of stock bikes out there today.
To read an overview of Harley-Davidson staging please click here or click here to return to our Harley-Davidson stage 3 article (stage 2 & stage 1 are here)
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