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 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 seat cutting machine.

MODEL: 2001-05 Yamaha Raptor 660

DRI HP4 PURCHASE OPTIONS

DR-280K $895.00 DRI Valve Train HP4 Kit Camshaft (see cam profile options below), HD Valve Springs w/Titanium Retainers, Shortened Valve Guides, Big Valve Kit (+1.0mm S/S Intake and Exhaust Valves) ONLY
* Porting / Serdi Valve seat cut not included in this kit.
**Kit must be installed by a trained professional with proper equipment.
** Customer must also send in stock cam core. (or pay core charge)

DR-280KP $1350.00 DRI Valve Train HP4 Kit Camshaft (see cam profile options below), HD Valve Springs w/Titanium Retainers, Shortened Valve Guides, Big Valve Kit (+1.0mm S/S Intake and Exhaust Valves), Cylinder Head Porting , SERDI Valve Seat Machining and Professional Head Assembly .
*Customer must send in head for modification or purchase new head from DRI
** Customer must also send in stock cam core.
(or pay core charge)

CAMSHAFT OPTIONS
CORES REQUIRED: Head Assy, Camshaft.
*NEW CORE PRICING: Cylinder $440.00, Head $799.00, Cams $215.00
INSTALLATION: Kit must be assembled by a trained professional
DELIVERY TIME: 2-4 weeks

X1H Grind Camshaft
Part #280-X3H
Specifications: Bottom/Midrange Cam, Lift: .452”/.429", Duration 276°/274°
Application:Dune Riding/ Trail Riding/Woods/Cross Country

X2H Grind Camshaft
Part #: 280-X14H
Specifications: Midrange/Top End Cam, Lift: .452”/.412", Duration 292°/294°
Application: Aggressive Sand Dune/Sand Hill and Drag Racing
Notes: 1,2,3,4,

*NOTES:
1. HD Valve Springs are required for this camshaft.
2. Shortened Bronze Guides are required for this camshaft.
3. New or modified piston required for this camshaft. Additional valve pocket relief in piston is required due to increased camshaft lift.
4. Customer must send in stock camshaft core. If no core is supplied, customer must pay core charge of $220.00
5. Rocker arm clearance (cam lobe to rocker) must be checked.
6.Rocker arms (both IN and EX) must be modified. Due to increased cam lobe size; material must be removed from rocker arms to allow for proper cam lobe to rocker clearance. Modification charge $75
7. Head casting must be modified to allow for camshaft to be installed in head.
(DR performs modification in KP kit)

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.

PISTON OPTIONS
Forged Piston Kits available in the following sizes and compression
*pistons sizes up to 102mm will work in stock cylinder
STD Bore(100mm), 101mm, 102mm
Compression options: 10-1, 11-1, 12-1
*Pistons larger than 102mm require big bore sleeve and may have adverse effect on engines reliability.

PIPE and IGNITION
For maximum performance, it is highly recommended to use a Fat Boy 4 Complete Exhaust System, Pro Flow Air Cleaner Kit, STD or Oversized High Compression piston kit, Vortex X10 CDI and upgrade carburetor system 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 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. process.

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.