January 25, 2011
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A serious internal engine mod that “long rods” the typical 250 four-stroke engine to squeeze the most out of it.
CONTACT? or (949) 567-9000.

Here’s a list of things that stand out with Carrillo’s Project X Platinum kit.

(1) Long rod.
The heart of the Project X Platinum kit is a longer connecting rod. Theoretically, changing the connecting rod length can create more mechanical advantage at certain parts of the engine cycle. It’s easy to visualize how the rod would sit at a different leverage angle through the stroke of the piston. The different angles reduce or increase side load pressure on the cylinder walls. Most old-school racers will remember the long-rod YZ250s of the 1990s.

(2) Execution.
The Project X Platinum kit has a 2mm longer rod. Room for the extended rod is provided by a 1mm smaller wristpin hole and a special piston that allows the rod to sit further up inside it. Carrillo admits that ideally it would be better to go even longer, but it would involve more expensive parts.

(3) Components. The Project X kit includes the longer connecting rod, special piston, DLC-coated wrist pin and top-end gasket kit. The kit increases the compression ratio to 13.5:1 (just slightly higher than stock compression). CP-Carrillo is currently working on a version with a 14:1 compression ratio.

(4) Construction.
Carrillo rods are made from proprietary chrome, nickel, moly and vanadium alloy. Their manufacturing process and materials are tested and checked by independent sources. It should be noted that very high demands are placed on the wristpin of an engine. Our short-term test can’t vouch for the durability of Carrillo’s smaller pin setup.

(5) On the track.
With several MXA test riders going back and forth between a bone-stock YZ250F and a bone-stock Project X long-rod YZ250F, the consensus was that the Carrillo gave up some bottom-end power, but made it back up through the middle and pulled better into the high rev range. The stocker was a little easier to ride, a little snappier down low and a better choice for a Novice, but the Project X bike was faster from the middle on up and pulled longer. Remember, the only difference between these two engines was the 2mm-longer rod. The downside of the long-rod kit was more engine braking.
WHAT’S THE SQUAWK? There are two things to consider: (1) Installation.
The kit requires a fresh bottom bearing and washer. Although these parts are available from Yamaha, some other OEM’s don’t offer them. (2) Target consumer. This kit is not intended as a stand-alone mod. The long-rod kit is designed to enable an engine builder to get more power up top without relying solely on cams and other mods. It’s far cheaper to go the cheater-big-bore-kit route. MXA tested it as a stand-alone mod because we wanted to isolate the effects of the change.

Aside from the increased engine braking, our Project X Platinum kit YZ250F was how the bike should run from the factory. It’s not a cheap mod, nor does it offer much by itself, but as part of a comprehensive engine program?it has a lot of merit.


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