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.

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 4-Stroke Head Builds incorporate DR’s HP4 Valve Train Kit. 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.

DRI HP4 BUILD OPTIONS (specify model year ‘04-05 or ‘06-’16)

DR-108KP $1795.00 DRI HP4 Valve Train Kit (04-07)
DR-140KP $1795.00 DRI HP4 Valve Train Kit (08-16) *Uses internal compression release
Includes: DR Cylinder Head Port , SERDI Valve Seat Machining, Head Reassembly and Valve Reshim,
Big Valve Kit (+1.0mm S/S Intake and Exhaust Valves), HD Valve Springs w/Titanium Retainers,
Shortened Valve Guides (required to clear hi-lift camshfts’s),
Billet Camshaft (see cam profile options below) MADE IN USA

NOTE: Customers Must Send In their Head/cam tower assy for HP4 build or purchase new head.
DRI offers New OEM Heads-Call for availability.

CAMSHAFT OPTIONS
X11 Grind Camshaft
Motocross Cam (Midrange/Top End Cam, Lift: .430”/.385", Duration 266? °/282? °)

X22 Grind Camshaft
Baja/Cross Country Cam (Bottom/Midrange Cam, Lift: .412”/.350", Duration 260 °/268 °)

X33 Grind Camshaft
TT/Drag Race Cam (Maximum Top End Cam, Lift .435”/.385" Duration 276 °)

*DRI uses Billet Camshafts ONLY for the TRX 450R. No core required.
**To insure highest quality, all camshafts used by DRI are made in the USA.

*** '08-16 TRX450 electric start model uses different mechanism. Use part #140-grind #.
All grinds are available in #140 -X11, X22, X33

VALVE OPTIONS
+1.0mm or +2.0mm Titanium Intake Valves add $2500(pr) to kit price ($399.00 per pair if purchased separately)
+2.0mm Stainless Steel Intake and Exhaust Valves also available call for details

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.

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 no 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