Project Turbo Hayabusa Part Two | Engine Internals

Sure, the Hayabusa's internals are fairly robust and can handle a power adder within reason, but push the limits and you'll be pushing your bike home-or worse. The cause of catastrophic engine failure can usually be pinpointed to the weakest link. Why take the chance?

This is precisely why we looked to RPM Cycle Performance for a helping hand in making our project 'Busa mega powerful, but also supremely reliable. The last thing we wanted to do was skimp on the engine internals for the sake of saving a little time and money, so we handed the bike over to Jason King and his crew to break down, build back up and tune to the moon.

Before he even bothered laying the Velocity Racing Stage 2 turbo kit out on the table, Jason dropped the motor and tore it down to its constituent components. With that done he could replace the majority of stock parts with sturdier aftermarket parts-most importantly the rods and pistons.

The standard conrods will be replaced with much stronger Crower parts rather than the stock rods that would fail under the stress. When you imagine the poor rods' job you can see why they need to be as strong as possible; they move to the top of the stroke and stop, then get pulled to the bottom and stop. They do this about 13,000 times per minute at full throttle and with a turbo speeding the process up there's considerably more force than the stock rods are capable of handling.

The pistons also need to be changed-not just so that they are stronger than the standard ones, but also to reduce the compression ratio. JE turbo pistons have a dished top that increases the volume of the combustion chamber at top dead center and reduces the base compression ratio to around 8.7:1. This is important since we'll be pumping in pressurized air from a turbo. If we stayed with the stock pistons and compression ratio of 11.0:1, the engine would suffer terrible detonation.

Because we fit new conrods, we had to make sure we chose the correct bearing shells for the big ends to give the required clearance between the crankshaft big-end journals and the bearings.

The Plastigauge is crushed into the space between the bearing and journal and spreads out into a flat line. Once the rod is unbolted and removed, the thickness of the squashed Plastigauge is measured, and this gives the clearance inside the bearing. The clearance is then checked with a chart in the service manual, and you can then select the appropriate thickness of bearing shell to give the proper clearance.

The most important parts of our internal engine build are the Crower conrods and JE pistons - these are essential to keep the engine from destroying itself. But we'd be foolish if we didn't also apply stronger head and crankcase studs to keep it all together. Sandwiched within the gaps are fresh new Cometic gaskets too. While the mildly glamorous rods and pistons get all the attention, the motor would surely fail without these additional components.

Some of the motor can stay stock however. The crankcases are fine and the crankshaft can handle much more than we're asking of it. Ditto the gearbox, though Jason did go the extra mile and undercut the trans for smooth, seamless, wide-open throttle upshifts.

It's important to understand there are cheap and easy ways to gain big power, but the motor won't last and you'll end up spending more in the long run than if you simply did it right the first time. With our engine properly reinforced we can ride confident and keep the throttle pinned without fear of a stock component letting go internally.