You are forgiven if you are a Honda CRF450, Kawasaki KX450F or KTM 450SXF owner and you don’t give a twit about hopped-up Yamaha YZ450Fs. You may be thinking, “Yamaha? I don’t own a Yamaha and don’t want to read about them.” But, you know deep down inside your insecure heart that you do want to know everything there is to know about the 2010 Yamaha YZ450F. Why? Because that is your competition.

The YZ450F was all-new in 2010, and every racer, on every brand, has to wonder if the YZ450F’s backwards cylinder, offset crankshaft, tilted top-end, downdraft fuel injection and creative frame offer a significant advantage over his trusty, but rusty, race bike.

In the 2010 MXA 450 Shootout, the Yamaha YZ450F finished second overall (behind the KTM, but in front of the CRF and KX-F). The MXA wrecking crews thinks that the Yamaha YZ450F is a solid machine with innovative credentials. It has a typically abrupt, low-to-mid, fuel-injected powerband; is relatively flat on top; and does not come near the horsepower output of the KX450F or 450SXF. As for the handling, the YZ450F feels light in roll, pitch and yaw, but since it is heavier than the 2009 YZ450F, some of the benefits brought on by centralization of mass are muted. The front end has a no-bite feel on the entrance to turns, but overall it handles decently. All in all, the 2010 Yamaha YZ450F is a good motocross bike?not a great one, though, because it needs more power, improved top end and a sleeker layout.

To that end, the MXA wrecking crew ordered up four full-race, hopped-up 2010 YZ450F project bikes. We told Hot Cams, AP Racing, Yoshimura and Pro Circuit that there were no holds barred?choke holds, arm bars and knee drops were allowed. They were asked to build the ultimate expression of what a YZ450F could be.

What follows is what the MXA test riders thought about the four YZs…this is a test of one of them?AP Racing’s YZ450F. Last week we tested Yoshimura’s YZ450F and you can find it on the home page.

WE TEST THE AP RACING YAMAHA YZ450F

ALL THE PERTINENT FACTS
Here are the details, prices and parts used on AP Racing’s 2010 Yamaha YZ450F:

ENGINE:
1. L.A. Sleeve porting with five-angle radius valve job ($500.00).
2. L.A. Sleeve cam grind ($350.00).
3. L.A. Sleeve dyno EFI tuning ($175.00).
4. CP high-compression MX1070 piston ($307.00).
5. Hinson clutch cover ($159.99), pressure plate ($189.99), inner hub ($309.99).
6. Trick 114-octane racing fuel $10.29 (five gallon), $9.09 (gallon), $8.74 per gallon by drum.

EXHAUST:
1. DR.D Ti/Ti complete system ($869.99).

SUSPENSION:
1. Precision Concepts suspension revalve ($397.67).

ACCESSORIES:
1. AP Racing front and rear brake pads ($35.99 each).
2. AP Racing PRF high-temp brake fluid ($32.99).
3. DR.D radiator lowering kit ($49.99).
4. DR.D hour meter and bracket ($49.99).
5. AME white full-waffle grips ($9.95).
6. Dunlop Geomax MX 51 front and rear tires.

CONTACTS:
AP Racing: www.apbrakesusa.com or (562) 945-1098.
L.A. Sleeve: www.lasleeve.com or (562) 945 7578.
CP Pistons: www.cppistons.com or (949) 567-9000.
Precision Concepts: www.precisionconceptsracing.com or (951) 697-8488.
Hinson Clutch Components: www.hinsonracing.com or (909) 946-2942.
Trick Racing Fuel: www.trickgas.com or (800) 444-1449.

ENGINE BY L.A. SLEEVE AND SUSPENSION BY PRECISION CONCEPTS

MXA gets to test dozens of decked-out project bikes every year. The question readers ask most is not about the performance of the machine, but “What happens to the bike after the test?” The answer varies, but MXA never keeps its test bikes. Why not? First, we have more bikes on the way to test and, second, they don’t belong to us. Most project bikes are sold or raced by the companies that invested the money into building them. The AP Racing YZ450F project bike falls into this category. Owned by L.A. Sleeve, this project bike was to showcase their products. When we were done with it, it continued to serve as a tool for further development for L.A. Sleeve and AP Racing.

AP Racing was somewhat up in the air about whether to equip their project bike with an oversized front rotor or not. In the end, they let their brake pads and fluid stand alone. AP got the brakes up to snuff and then sent the bike to L.A. Sleeve for engine work and to Precision Concepts for suspension modifications.

The consensus among engine tuners is that the 2010 YZ450F doesn’t respond as well to high compression as other bikes (although it can be made to work as part of a multi-prong modification plan like piston, porting and cams). Luckily, porting is a specialty for L.A. Sleeve. They massaged the head of their YZ project bike for better intake and exhaust flow and added their five-angle radius valve seat mod. Then they installed a high-compression CP piston. We had to run Trick 114-octane gas to accommodate the raised compression.
 
Under pressure to get the project bike done, L.A. Sleeve wasn’t able to do all the testing that they would have liked with higher lift cams. They settled on a simple grind with modest improvement. They also removed the airbox screen and a thin layer of foam under the air filter.

Another cool L.A. Sleeve service is ignition remapping to insure that your power package is complete and running at its full potential. Incidentally, L.A. Sleeve isn’t a big fan of the 2010 GYTR Power Tuner?which MXA believes is easy for the average racer to use but has limited capabilities for serious engine tuners. Still, the mapping was an important part of the setup.

Given that we didn’t tell AP exactly which MXA test rider to set the bike up for, Precision Concepts felt that it was best to utilize the stock springs and revalve the suspension for an all-around, middle-of-the-road setup. To get the most out of the stock suspension, Precision Concepts relies on feedback from their sponsored riders, which include Marty Smith and Robby Bell.

MXA TEST RIDER COMMENTS:

“The engine was plenty fast from low-to-mid. It was kind of barky, aggressive and itching to go. The throttle response wasn’t as jerky as on the stocker, but it was still instantaneous.”
 
“It took a purposeful mindset to race the AP YZ450F. The powerband was low-to-mid, which meant that there wasn’t as much top-end as with some of the other test bikes. It was strong off the bottom and really pulled hard into the mid-range. You had to shift?but not short-shift?to get the most out of it.”
 
“The AP Racing YZ450F had the barkiest sensation of power delivery of all the YZ450Fs in this test. It hits in the middle and pulls hard, but signs off on top.”

“The high-compression CP piston required high-octane race gas. To me, that was a clue that this bike was going to hit hard and sign off early, which is exactly what it did. When you up the compression on a 2010 Yamaha YZ450F, you get an engine that chugs up and chugs down. It was too much piston, and I’d be willing to bet that just the L.A. Sleeve head mods and cam grind would have delivered a more fluid powerband.”
 
“The Precision Concepts suspension had a weird feel. It almost felt like an offroad bike. Its worst trait was that it stayed high in the rear just like the stocker (which makes sense since it had the stock springs up?front and in the rear). It worked best on small, skittery-type bumps. It gave up some performance in big G-outs.”

“I didn’t like the way the shock felt at first, but after fiddling with the fork height on the front, ride height in the rear, and the compression on the shock, I felt like it came around.”
    
“This is a chassis that doesn’t like out-of-balance suspension. If the front is too low or the rear is too high, the YZ450F will wiggle on the entrance to corners. That is irritating. The Precision Concepts suspension didn’t help the handling as much as it could have.”
 
“Looking at the bike as a whole and considering the target for the suspension and powerband placement, the AP Racing bike is a good package for an intermediate rider who takes his racing seriously. It doesn’t have enough top-end power to suit a Pro and was too abrupt down low for a Novice. The engine and the suspension had a unique flavor that would probably only suit a rider with unique tastes.”