Big bore kits from Thumping Racing

The Big-Bore Kits have been designed with reliability and usable power in mind, the pistons have been specifically designed by Wiseco, using technology currently being used in NASCAR racing. The pistons therefore have been lightened (for high reving) but still retain the extra strength that Wiseco forged pistons are reknown for. The overall result is loads more power throughout the rev range whilst allowing the engine to rev to the moon !

Thumper Racing's Big-Bore kits are currently being used by some US Factory Teams.

If we haven't listed your make or model and you require a kit for your bike, please Email us for info there are many different kits available.

Wiseco have specially developed a piston that is light as a feather, but HARD as nails.
The end result, a kit that has stump pulling power and still revs to the moon!

These kit's are available complete or as individual components.

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HondaKawasakiSuzukiYamahaKTM
XR400 kit
XR250 kit
TRX400 kit
XR600 kit
KLX250 kit
KLX300 kit
DR350 kit
DRZ400 kit
LTZ400 kit
 YZ/WR250F kit
YZ/WR400F kit
YZ/WR426F kit
YZ/WR450F kit
 KTM250 kit
KTM400 kit

Honda XR400 kit 400cc - 440cc

The full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
  • Big-bore sleeve.
  • Big-bore gasket kit.

    • Price

    XR400 kit - 440cc WAS £365 NOW £240 + postage.

    Honda XR250 kit 250cc - 280cc

    The full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
  • Big-bore gasket kit.

    • Price

    XR250 kit - 280cc WAS £295 NOW £185 + postage.

    Honda TRX 400EX Kit - 440cc 97-03

    "Here we have the 440cc kit, Wiseco have specially developed a piston that is light as a feather, but HARD as nails. The end result - a kit that has stump pulling power and still revs to the moon.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
  • Big-bore sleeve.
  • Big-bore gasket kit.
  • Your cylinder will require boring and sleeving
    • .

    Price: £240.00

    Honda XR 600 Kit - 660cc

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.

    • Price: £250.00

    Kawasaki KLX 250 Kit - 300cc

    "With Nikasil coated water-cooled cyclinder, the largest bore that can be safely made for the 250 is 78mm, giving 292cc. The 42 extra cc give the engine the bottom and mid-power that should have been there originally. Retune the stock carburetor and the engine starts quickly and reliably."

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.

    Price: £295.00

    Kawasaki KLX 300 Kit - 340cc

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £250.00

    Suzuki DR 350 Kit - 435cc 1990-99

    "Others have tried big bore kits for this engine, with limited success. Our testing showed that the best solution for improving the power was with a bigger bore, leaving the Valve train stock giving an affordable and reliable solution to gaining more power. We have done extensive lightening on the piston and included a NASCAR style piston pin for reliability, while increasing the displacement to 435cc. The result is dramatically improved bottom and mid RPM power increases."

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 88mm.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £330.00

    Suzuki DRZ 400 Kit - 440cc Or 470cc

    Here we have the 440cc kit, as used by Team Suzuki USA on Mike Kiedrowski's bike or its bigger brother, the 470cc kit. The 440 kit is a good all rounder where as the 470 kit is designed as a full race kit.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, (440cc - 94mm) (470cc - 97mm).
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Prices

  • 440cc Complete Kit £295
  • 470cc Complete Kit £325

    • Suzuki LTZ 400 Kit - 440cc Or 470cc

    Here we have the 440cc kit or its bigger brother, the 470cc kit. The 440 kit is a good all rounder where as the 470 kit is designed as a full race kit.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, (440cc - 94mm) (470cc - 97mm).
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Prices

  • 436cc Complete Kit £260
  • 470cc Complete Kit £290

    • Yamaha YZ/WR 250F Kit - 280cc

    "We have been testing a 280 kit for this bike and are very happy with the results. The 250 in stock form is a good bike but the power is all at the upper end, this works good for alot of riders but many of you like us like bottom end and mid range. With these kits we were able to get the bottom power and still rev to the moon!! All of the riders that have tested the bike liked it better than the stock motor." This is an extract from the manufacturers test results.

    This kit is available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 80mm .
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and replating.
    • .

    Price: £180.00

    Yamaha YZ/WR 400F Kit - 430cc

    The YZF/WR has a good motor, but more power was available, therefore a 430cc kit has been developed. Using a steel sleeve any 400 can become a 430 and any 426 a 450. Both these kits give the motor more overall performance, boosting the bottom end. Giving you the grunt of a JOHN DEER and the top end speed of a DEER.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 95mm.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £235.00

    Yamaha YZ/WR 426F Kit - 450cc

    The YZF/WR has a good motor, but more power was available, therefore a 430cc kit has been developed. Using a steel sleeve any 400 can become a 430 and any 426 a 450. Both these kits give the motor more overall performance, boosting the bottom end. Giving you the grunt of a JOHN DEER and the top end speed of a DEER.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 97mm.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £249.99

    Yamaha YZ/WR 450F Kit - 470cc

    The YZF/WR has a good motor, but more power was available, therefore a 450cc kit has been developed. Using a steel sleeve any 400 can become a 430 and any 426 a 450. Both these kits give the motor more overall performance, boosting the bottom end. Giving you the grunt of a JOHN DEER and the top end speed of a DEER.

    These kit's are available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 97mm.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £235.00

    KTM 250 Kit - 300cc

    This kit is available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit.
    • .
  • Big-bore sleeve.
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and sleeving.
    • .

    Price: £235.00

    KTM 400 Kit - 450cc

    This kit is available complete or as individual components, the full kit comprises of:

  • Wiseco developed lightened, forged piston kit, 95mm .
    • .
  • Big-bore gasket kit.
    • .
  • Your cylinder will require boring and replating.
    • .

    Price: £175.00