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We are pleased to announce the partnership between Thumper Racing and DirtBikeStore.com.
We are importing their very unique products for you to enhance the look of your bike and enjoy the unrivalled performance that Thumper Racing products are renown for.

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 e-mail us for info as Thumper Racing supply many more kits!

Please see the foot of this page for limited warranty.


Honda XR 250 Kit - 280cc 86-06

Price:  £181.07 / €217.28 Including VAT at 15%
Model Year


These kit's are available complete or as individual components, the full kit comprises of:
  • Big-bore piston kit 77mm
  • Big-bore head gasket, base gasket
  • Heavy duty clutch springs

    Your cylinder will require boring. If required we can have this work carried out for you, POA  

    • Honda XR 400 Kit - 440cc 96-06

    Price:  £234.90 / €281.88 Including VAT at 15%

    "Here we have the 440cc kit, Wiseco have specially developed a piston that is light as a feather, but TUFF 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.
  • Heavy duty clutch springs.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA 

    • Honda XR 600 Kit - 660cc

    Price:  £244.69 / €293.62 Including VAT at 15%


    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.
  • Heavy duty clutch springs.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA 

    • Honda CRF 250 R/X Kit - 270cc 04-06

    Price:  £234.90 / €281.88 Including VAT at 15%


    This kit is available complete or as individual components, the full kit comprises of:
  • Wiseco developed lightened, forged piston kit.
  • Big-bore gasket kit.
  • Big-bore sleeve.

    Your cylinder will require resleeving. If required we can have this work carried out for you, POA 

    • Kawasaki KLX 250 Kit - 300cc

    Price:  £288.72 / €346.46 Including VAT at 15%


    "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.
  • Heavy duty clutch plates & springs.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA 

    • Kawasaki KLX 300 Kit - 340cc

    Price:  £244.69 / €293.62 Including VAT at 15%


    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.
  • Heavy duty clutch springs.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA 

    • KXF 250 04-05 RMZ 250 04-06 Kit - 270cc

    Price:  £176.17 / €211.40 Including VAT at 15%


    This kit is available complete or as individual components, the full kit comprises of:
  • Wiseco developed lightened, forged piston kit.
  • Big-bore gasket kit.

    Your cylinder will require boring and replating. If required we can have this work carried out for you, POA 

    • Suzuki DR 350 Kit - 435cc 1990-99

    Price:  £288.72 / €346.46 Including VAT at 15%

    "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.
  • Heavy duty clutch springs and clutch plates.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA
     

    • Suzuki DRZ 400 Kit - 440cc Or 470cc 00-06


    Choose



    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 - 94.50mm) (470cc - 97mm).
  • Big-bore sleeve.
  • Big-bore gasket kit.
  • Heavy duty clutch plates and springs (470cc kit).

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA 

    • Yamaha YZ/WR 250F Kit - 280cc 00-06

    Price:  £176.17 / €211.40 Including VAT at 15%


    "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. If required we can have this work carried out for you, POA
     

    • Yamaha YZ/WR 400F Kit - 430cc 98-00

    Price:  £230.00 / €276.00 Including VAT at 15%


    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.
  • Heavy duty clutch springs.

    Your cylinder will require boring and sleeving. If required we can have this work carried out for you, POA  

    • Yamaha YZ/WR 426F Kit - 450cc 00-02

    Price:  £230.00 / €276.00 Including VAT at 15%


    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. If required we can have this work carried out for you, POA  

    • Yamaha YZ/WR 450F Kit - 470cc 03-06

    Price:  £230.00 / €276.00 Including VAT at 15%


    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. If required we can have this work carried out for you, POA  

    • Yamaha TTR 250 - 325 96-06

    Price:  £244.69 / €293.62 Including VAT at 15%

    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. If required we can have this work carried out for you, POA
    Your crankcases will need to be machined to take the larger diameter sleeve. 

    • KTM 250 Kit - 300cc

    Price:  £230.00 / €276.00 Including VAT at 15%


    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. If required we can have this work carried out for you, POA  

    • KTM 400 Kit - 450cc

    Price:  £171.28 / €205.54 Including VAT at 15%


    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. If required we can have this work carried out for you, POA


    •  


    Thumper Limited Warranty

    Since all items manufactured by Thumper Racing are intended for competition use, they are sold as is with no warranty, expressed or implied. Thumper Racing will how ever, at their discretion, repair or replace any item that they judge to be defective in workmanship or materials. Their and our liability under this replacement policy extends only to the original purchase price of the item and does not include incidental or consequential damages. Products sold on behalf of Thumper Racing but produced by other manufacturers, may be covered by their own warranties, if any. However we make no representation as to the life span of these products or the products of others under race conditions. Any faults induced when fitting these kits are solely the responsibility of the individual or company carrying out the work.  
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