The Hayabusa rolling chassis waits patiently for its heart to be built bigger and stronger.
Low compression pistons (from JE) are a crucial component in our preparation for big turbo boost.
Stock rods (above) can't handle the massive strain that the stronger Crower rods (right) are designed to cope with.
If you were given six hours and a million dollar award incentive, could you get this hodgepodge running again?
There's an easy way and then there's the right way. All too often we see bikes that claim big horsepower numbers after bolting on a turbo or adding a huge nitrous spray, but those engines are on a timer and could blow at any moment. Why? They've been externally built without regard for the internals. Anybody can build a beautiful house out of plywood, but without a solid foundation would you dare live within its walls? The same is true when extracting big power from a motor.
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.
Measuring this tiny distance is very tricky, and the tool for the job is a strange substance calle Plastigauge. This is a carefully manu-factured strip of plasticine-like material that you put inside the bearing, and then assemble the rod around it. You then torque the bolts to spec.
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.
Making big power is one thing, but getting it to the ground is another story. A stock transmission works well in the application it was designed for, in this case a 170 horsepower engine. When that power is doubled, so is the force on the transmission. To ensure that each shift hits home-and stays engaged instead of falling out of gear-many modified engines will utilize an undercut transmission. This means that a mechanic essentially grinds away the part of the gear "dog" and slot that are used during upshifts so that they engage better
This is yet another bit of "insurance" against your big power engine shredding the weak stock components, because once the engagement dogs are worn away you're looking at a new transmission. RPM Cycle Performance performed this procedure in house while the engine was apart, meaning any missed shifts will be due to our own pussyfooted clicks-not the transmission.
A strong billet clutch basket can handle all of the extra power going through it, where the stock basket would simply fail and slip. A lockup clutch won't slip at higher revs when the big power is being unleashed. As you engage the clutch and the clutch assembly spins, the lock up adds progressive pressure with adjustable weights on the hub until it will be clamped tightly at max RPM and not allow clutch slippage, thus getting all your power to the tire instead of losing some in the clutch basket. RPM Cycle Performance builds and supplies lock up clutches, so in one went.
The unsung heroes of any motor are its gaskets. Whether you need to raise or lower compression with an alternate (or custom) sized head gasket or simply want to keep oil from leaking our of your clutch cover, the gasket is largely responsible. Instead of trying to piece together a kit at a dealership we simply went to Cometic and snagged a full engine kit. Trying to reuse old gaskets isn't a good idea, so don't cut corners in this part of your engine build.
Crower Billet Steel Rods
**JE Pistons Turbo Pistons
**Cometic Full Gasket Kit
**RPM Cycle Performance
** We came across this one-stop shop when we were researching Velocity Racing. It turns out that RPM Cycle Performance recently bought Velocity-a move that makes sense because RPM had already played an integral part in the production of Velocity's turbo kits.
Along with providing the full line of Velocity products, RPM also offers some of its own go-fast gear like the lockup clutch and oil pan we're running on our 'Busa. The allure to a shop like RPM is that you can ship your stock bike there, and when it's returned it'll be built, tuned and ready to ride.
Next Month: Turbo installation and tuning