Big Bore Thumpers offers the ultimate CR450R and CRF250 R/X cylinder head solution with APE stainless valve conversions. These conversions completely eliminate the problem of oem valved beating themselves into the seats and the lash tightening up. Install APE conversion and spend more time riding and less time working on the motor. World famous APE valve springs are made from premium chrome silicone wire for consistant pressure and excellent fatigue life. Racers as well as street riders have come to depend on APE springs for winning performance. We have had over 30 years experience designing valve springs for the most high-performance motorcycle engines. APE valve spring retainers are CNC machined in-house from aircraft quality titanium bar stock. Special gauging fixtures allow dimensions to be held close to provide exact installed heights when assembling the cylinder head.


BRAND NEW Honda cylinder head with the ports matched to the seats and all of the Stage Two components installed: special stainless/steel intake and exhaust valves, heavy-duty valve springs and titanium retainers.

Ready to bolt on. This is an outright purchase with no core required.

To purchase these cylinder heads fully race-ported, click here.


CRF450 THRU '06 #H450HS-3 $549.95 (order this item online!)
CRF450 THRU '08** #H450HS-08 $575.00 (order this item online!)
CRF250 #H250HS-3 $575.00 (order this item online!)

**Part #H450HS-08 is an '08 cylinder head which will fit both early and late model CRF 450s. For bike-owners who favor the 08 intake tract and the smaller exhaust valve, we offer this package using this '08 CRF450 cylinder head.


TRX450R 04-05 #TRX450-4 $575.00 (order this item online!)
TRX450R 06-09 #TRX450-9 $549.95 (order this item online!)

Note:Unlike the motorcycle heads, these early and late ATV heads are not interchangeable.