RVF750-RC45 Engine Tuning

The RC45's engine is a 749cc liquid cooled 90deg V4. Four valves per cylinder are operated by overhead cams driven by a side mounted gear train. All RC45's use the same bore and stroke of 72.0 x 46.0mm.

As standard the motor is very good, capable of making around 128rwhp with the right external modifications. This figure can be increased with some detailed internal work though.

Before any work is attempted you must have a clean working area and a lot of space. An RC45 motor has many parts!

There are a number of components that can be upgraded or re-worked inside an RC45; here are just the basics.


RVF750 HRC Port Mods | Click to enlarge

The stock cylinder head is quite good, however work can be done to both inlet and exhaust ports to bring them up to HRC spec.

Using the following diagrams the stock heads can be modified. Remember to be very careful not to damage the cylinder head face as repairing it can be tricky.

Great care must be taken when grinding the valve guides. Once the ports have been ground, fit the inlet manifolds to the cylinder heads and mark them, and then using a light sanding wheel remove the difference between the two to promote smooth gasflow between the components.


RVF750 HRC Crankcase Mods | Click to enlarge

To increase the oil pressure to the main and big end bearings HRC suggest that the fly wheel oil bleed hole is filled. This is done using a small alloy plug. Apply epoxy resin to the plug before fitting then stake punch around it after installation.

In 1996 HRC introduced new oil pump driven and drive sprockets. These geared the oil pump down to help increase hp by reducing oil flow. This is a modification we would not recommend for most RC45 motors used on the road.



A number of pistons were available, some using a single compression ring and oil control ring, others using two compression rings with an oil controller. These had increased compression over the stock piston. Compression is one of the few areas the RC45 motor lacks. To get good power increases the use of the higher compression pistons are a great help.

How to tell a HRC piston from stock? Stock pistons only have dimples in the inlet valve pockets, the HRC pistons have dimples in both inlet and exhaust pockets.


Again HRC produced cams. These can be fitted to a stock motor as long as the HRC valve spring kit is used. However the HRC cams are designed to work at higher RPM's than the standard electrics will allow the motor to spin too. So unless you have the HRC electrics kit the stock cams work very well and will not hold the motor back.

HRC cams have 1.5mm more lift on the inlet and 0.3mm more lift on the exhaust, as well as more duration.

RVF750 Valve Clearance for HRC Cams
Inlet 0.2mm ± 0.02mm
Exhaust   0.3mm ± 0.02mm

These cams also have the quietening gears removed but the timing marks are the same as standard.