Ultimate Motorcycle Performance Products and Services

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John Blackwell's Blown VMAX

The History of this Project

We received this engine with burnt pistons from a blower set up that ran way too lean.

It was torn it down and over-bored to 78 mm using the stock sleeves.

John at JE pistons made a set of low compression 8.5 to 1, dished pistons specifically designed for blower or boost applications.

 

We replaced the connecting rods with the later model Y-19 Yamaha pieces and had to micro-polish the main and rod journals on the crank. After boring and finish-honing the block, it was machined for copper o-ring wire to be installed in the top of the sleeve flange. This allows us to use a .043" copper head gasket for high pressure sealing.

We installed a set of our adjustable cam sprockets to set the final cam timing at 104/109 (intake/exhaust).

The final touch was done by Brendan, our carburetor tech. He transformed the 390cfm Holley four barrel to function in the blown, draw-through application. These carbs come from the blower supplier with no mods done at all. We contacted Holley and they faxed us complete instructions to modify this 390 for blower use.

We also went one step further and changed the secondary from vacuum to mechanical. This makes a huge difference in air fuel ratio and exhaust gas temp in the mid range.

 
The last touch was our "Pro-Oiler" system which greatly increases the amount of oil pressure to the connecting rod bearings. This system also eliminates the o-ring blow out problem with a hand fabricated oiling manifold that is in one piece, not a group of separate pipes.

Since we did not have John's blower, we shipped his engine back to him to be run on the dyno near his home in South Carolina. It made 150 hp at the tire in low boost mode (4 to 5 psi).

The dyno tech said that the air fuel ratio was on-the-money and John has been riding the wheels off it ever since.