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.

Product Information:

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.

YAMAHA RAPTOR 250 DRI HP4 VALVE TRAIN KIT PURCHASE OPTIONS

OPTION #1
DR-275KP $995.00 DRI Valve Train HP4 Kit with DRI porting/SERDI valve seat machining Kit Includes: Camshaft Hard-faced on stock OEM core (see cam profile options below), HD Valve Springs w/Titanium Retainers, Shortened Valve Guides, Big Valve Kit (+1.0mm S/S Intake), DRI Cylinder Head Porting , SERDI Valve Seat Machining and Professional Head Assembly w/Porting, SERDI Valve Seat Cut and Assembly*
DRI custom matches the intake manifold to the intake port on all Raptor 250 heads. Once this process is completed it is inadvisable to change intake manifolds. This custom service is included in the porting process all clients have to do is send in their intake manifold with their head or purchase a new manifold from DRI.
*Customer must send in head for modification or purchase new head from DRI.
** Customer must also send in stock cam core.
** Customer must also send in stock intake manifold to be port matched to Intake port
*** Hard face rocker modification is recommended- Not included in above price- add $75.oo to hard-face each rocker. $150 pair.
Customer must send DR their stock rockers to be modified or buy new from DR>
CORE PRICE for Option # 1
New Head Charge- $362.00
Cam Core charge-$112.00
Intake Manifold-$37.98
Rocker Arm Core $53 ea.

OPTION #2
Complete Head assembled with HP4 kit, camshaft, rockets, intake manifold $ 1595
-Customer sends not core to purchase this head-
-Heads are built when ordered. Ordered must be prepaid.
-Average build time 6-8 weeks.
-Heads are shipped complete ready to run

CAMSHAFT OPTIONS
Full Race Cam- Best Top End (Lift .400/.400, Duration 282/286)
Motocross Cam – Midrange Power (Lift: .368”/.368", Duration 270°/268°)
Baja/Cross Country- Bottom End Power (Cam, Lift: .353”/.353", Duration 262°/257°)

*DRI use hard faced cams built on stock cores.
**To insure highest quality, all camshafts used by DRI are made in the USA.
*** For maximum reliability hard faced rockers are recommended.
Rocker modification $75.00ea/$150 pr. stock oem rocker core required

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 (see below)
280cc Big Bore Kit $595
NOTE: DR strongly recommends Nikasil bore on all Raptor 250 cylinders. Nikasil offers superior cooling, increased performance and better reliability than steel sleeves.
Race gas recommended on all

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)

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

AMPCO 45 Shortened Valve Guides allow for usage of high lift camshafts. Port side of guides are modified to improve air/fuel flow through ports.

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 in stock ready to build.

HORSEPOWER
HP4 Kits with porting offer gains up to 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 NATIONAL Exhaust with all HP4 Kits.
DR Has redesigned the Raptor 250 Fat Boy 4 exhaust system for Improved Power

Vortex CDI has been discontinued by mfg.

HIGH COMPRESSION PISTONS and BIG BORE KITS
For maximum performance, it is highly recommended to upgrade piston kit with either a forged high compression piston kit or a big bore kit. DRI offers the following:

STANDARD BORE 250cc PISTON KITS (subject to availaibility)
Piston Kit STD bore 10-1 Compression $225.00
Piston Kit STD bore 12-1 Compression $235.00
Piston Kit STD bore 13.5-1 Compression $225.00 special order
*Cylinder hone recommended, pistons work in stock cylinders.
** Pistons subject to availability

BIG BORE KITS
*stock cylinder MUST be modified to accommodate big bore pistons. Cylinder must have nikasil plating stripped off, cylinder bored and cylinder re-plated and honed.
**Customers can send in their cylinder for modification or purchase new modified cylinder from DRI.

280cc Big Bore Kit 12-1 compression $650.00 (kit includes 280cc 12-1 Big Bore forged piston kit, Big Bore Head gasket, Cylinder Modification-customer send in cylinder)

280cc Big Bore kit with New cylinder $999.00 (customers send in nothing)

10-1 piston kits have been discontinued


NOTE: DR strongly recommends Nikasil bore on all Raptor 250 cylinders. Nikasil offers superior cooling, increased performance and better reliability than steel sleeves.
Race gas recommended on all
280cc is largest big bore piston that can be installed in stock cylinder core with using steel sleeve.

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