Note: This is a specialty product and is not currently available for purchase online. Please call Duncan Racing International and a DRI staff member will assist you by collecting the required specifications and placing your order. Thank you.

Models '04-'09

With today's modern ATV 4-Stroke engines, making additional Horsepower is no easy task...This makes it critical that Engine Tuners have the Experience, Knowledge and Equipment to do the job properly.

Duncan Racing International's HP4 Valve Train Kit is designed to give you the utmost in performance and reliability by using the most advanced equipment and techniques in the industry. All porting work is performed by our master technician and valve seat cutting is done on our in-house SERDI valve grinding machine.


PURCHASE OPTIONS
DR-289K $1195.00 DRI Valve Train HP4 Kit ONLY*
Kit must be installed by a trained professional

DR-289KP $1695.00 DRI Valve Train HP4 Kit w/Porting, SERDI Valve Seat Cut and Assembly*

*Customer must send in head for modification or purchase new head from DRI for $556.45
**Customer must send in stock cam cores so DRI can remove IN and EX Cam sprockets and Compression Release Mechanism and install them on new Billet Camshafts.


CAM SHAFT OPTIONS
X12 Grind Camshaft
Motocross Cam (Midrange/Top End Cam, includes IN & EX Cams, Lift: .362/.353", Duration 262°)

X34 Grind Camshaft
Baja/Cross Country Cam (Bottom/Midrange Cam, includes IN & EX Cams, Lift: .350/.340", Duration 250°/253°)

*DRI uses Billet Camshafts ONLY for the YFZ 450.
**Customer must send in stock cam cores so DRI can remove IN and EX Cam sprockets and Compression Release Mechanism and install them on new Billet Camshafts.
***To insure highest quality, all camshafts used by DRI are made in the USA.

ADDITIONAL OPTIONS
Big Bore Kits and alternate compression ratio pistons are also available to use in conjunction with the HP4 Kit. Check the Big Bore Kit and Piston sections on our site for more info.

HP4 KIT FEATURES
In-House Cylinder Head Porting* (by Master Technician)
*Valve guides are removed during porting process to allow for greater port reconfiguration

Port Design Modifications Aided by In-House Flow Bench Testing and Computerized Port Mapping Software

Precision Valve Seat Machining and Reconfiguration*
*DRI uses in-house SERDI Valve Seat Cutting Machine used by F1, CART and NASCAR.

Big Valve Kits (Stainless Steel or Titanium)

Heavy Duty Valve Spring Kits*
*With Titanium Retainers, Mandatory with High Performance Valve Trains

AMPCO 45 Shortened Valve Guides

Camshafts of the Highest Quality Made in the USA

All Head Work Done In-House for Reasonable Turnaround Delivery Time.

Customers Can Send In Their Head for Modification or DRI Carries New OEM Heads.

HORSEPOWER
HP4 Kits with porting offer gains up to 5 HP*.
*Results vary depending on camshaft profile and piston compression.

PIPE and IGNITION
For maximum performance, it is highly recommended to use a Fat Boy 4 Complete Exhaust and Vortex Ignition with all HP4 Kits.

KIT INCLUDES
Camshafts, HD Valve Springs w/Titanium Retainers, Shortened Valve Guides, Big Valve Kit, Cylinder Head Porting (Optional), Valve Seat Cutting (Optional) and Professional Installation (Optional).

IMPORTANT NOTE When installing a high performance camshaft it is the responsibility of the engine assembler to check and confirm that the piston to valve clearance is adequate. Minimum clearance is .060" from valve to piston at peak lift. Tolerances can and will vary from engine to engine. There is not substitute for checking that these tolerances are correct. This is especially critical when mixing camshaft and pistons from different engine builders. One of the correct and easiest ways of checking this is by using the "claying the piston dome" method.
Call DRI or consult a professional technician

Kits include Camshaft(s), HD Valve Springs, Shortened Valve Guides and Big Valve Kit. The HP4 kit is the ultimate valve train upgrade for your sport or racing ATV.