Finally great performance at a great price. We at Janssen Motorsports try to cater to all our customers and realize that not everybody wants a national caliber engine.

So, we have developed our 1mm big valve head modifications. We start off by providing intake and exhaust porting. We then over bore all the valve pockets in the head to provide clearance for the 1mm oversized seats and valves. We then proceed to assemble stainless steel valves. These valves are a very durable alternative to the stock YFZ valves. We then follow up with new keepers, guides and high strength springs.

The end result is a great head that when combined with the correct components is very capable of producing dyno numbers in the 50 hp range. Valve clearance in the piston will be required and can be performed for an additional cost. The price requires your stock head as a core

These heads are available in two configurations. The 06 casting with these head mods is recommended for tighter mx or supercorss style tracks. The 05 casting with these head mods is recommended for larger mx tracks or flat track / TT racing.