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 grinding machine.

DRI HP4 PURCHASE OPTIONS

DR-166KP $1195.00 DRI Valve Train HP4 Kit
Includes: DR Cylinder Head Porting , SERDI Valve Seat Machining and Assembly
Hardfaced Camshaft (see cam profile options below), HD Valve Springs w/Titanium Retainers, Shortened Valve Guides, New STD S/S IN & EX Valves
(+1 mm S/S IN Valve are ONLY AVAILABLE by SPECIAL ORDER: add $135 each valve; $270 pr),
*Customer must send in head for modification
*Customer must send in stock cam core or pay an additional core charge of $140.00.
*Hardfaced rocker arm modification recommended. $125.00 each rocker. Customer must send in rocker arms to DR for modification

CAMSHAFT OPTIONS
166-05 Grind Camshaft
Motocross Cam (Midrange/Top End Cam, Lift: .336”/.385", Duration 249°)

166-25 Grind Camshaft
TT/Drag Race Cam (Maximum Top End Cam, Lift .370/.385" Duration 272°)

*DRI only offers hard faced cams built on stick cores. Customer must send in their stock cam or pay a core charge of $140.00.
**To insure highest quality, all camshafts used by DRI are made in the USA.
Hardfaced rocker arm modification recommended. $125.00 each rocker. Customer must send in rocker arms to DR for modification

VALVE OPTIONS
STD S/S IN Valves
OVERSIZED VALVES +1 mm S/S IN Valve are ONLY AVAILABLE by SPECIAL ORDER: add $135 each valve; $270 pr
SPECIAL ORDER VALVES Can Take 6-8 weeks to have mades
STD EX Valves Only

ADDITIONAL OPTIONS;
Alternate compression ratio pistons are also available to use in conjunction with the HP4 Kit.
Call DR for available options
BIG BORE KIT NOT AVAILABLE for 250X/300EX

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

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

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 3-4 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
(DISCONTINUED for this model) and DRI modified CDI 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.

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.