November 16, 2010
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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?Pro Circuit Racing’s YZ450F.  Over the last three weeks we have tested Yoshimura’s, AP Brakes’ and Hot Cams’ YZ450F and you can find them on the home page.


Here are the details, prices and parts used on Pro Circuit’s 2010 Yamaha YZ450F:

1. Pro Circuit four-stroke head porting ($549.95).
2. Pro Circuit intake valves ($349.95).
3. Pro Circuit exhaust valves ($349.95).
4. Pro Circuit camshafts with spring seats ($914.95).
5. Pro Circuit high-compression piston ($264.95).
6. Pro Circuit clutch springs ($79.95).

1. Pro Circuit Ti-4R race system ($999.95).
2. RC-4 header, it gives a little power and helps with sound.

1. Pro Circuit fork revalve and setup ($179.95).
2. Pro Circuit fork revalve internals ($169.75).
3. Pro Circuit shock revalve and setup ($149.95).
4. Pro Circuit shock revalve internals ($75.75).
5. Pro Circuit fork springs ($129.95).
6. Pro Circuit shock spring ($129.95).
7. Pro Circuit specialty shock kit for Showa ($119.95).
8. Pro Circuit MX spring tube ($289.95).
9. Works bladder cap kit ($74.95).
10. Pro Circuit shock linkage arm (1-1/2mm longer), ($224.95).

1. Pro Circuit axle blocks, radiator hose kit, flow-through titanium footpegs, rear brake clevis, banjo bolts, top and bottom triple clamp, 1-1/8-inch oversize bar mounts, and hour/tach meter.
2. Top clamp stock offset ($199.95), bottom clamp stock offset ($299.95) and oversize bar mount ($99.95).
3. Radiator hose kit ($84.95).
4. Ti pegs ($239.95).
5. Rear brake clevis ($54.95), Banjo bolt (set of two) ($44.95)
6. Pro Circuit hour/tach meter ($44.95).
7. Renthal sprocket ($64.95), Kevlar dual-layer grips ($19.95), Renthal TwinWall handlebars (price $119.95).
8. One Industries 10 Yamaha graphics kit with seat cover included ($189.95).
9. RK gold chain GB520MXZ4 ($97.97).

Pro Circuit Racing: www.procircuit.com or (951) 738-8050.
Renthal: www.renthal.com or (877) 736-8425.
RK Chain: www.rkexcelamerica.com or (760) 732-3161.
One Industries: www.oneindustries.com or (800) 663-5567.


Pro Circuit is a huge company that prides itself on being a one-stop shop for complete bike overhauls. They offer hop-up parts and services for every major brand and model released. So, when a new bike, like the 2010 YZ450F, makes its debut, Pro Circuit’s research and development runs like clockwork to update their line and figure out the best modifications.

Pro Circuit suspension guru Bones Bacon realized that the 2010 YZ450F suffered from the stinkbug syndrome. Some of his test riders were running 105 to 108mm of sag to compensate for the high-in-the-back feel. Bones talked with Yamaha factory engineers and decided to build a 1.5mm-longer link arm. This lowered the rear end, brought the sag back into the 100mm range, took some load off the front and addressed some wallowing issues of the stock setup. In addition to the link, Bones revalved the shock to calm it down. He also increased rebound quite a bit on our project bike.

Additionally, Bones discovered that the sideways YZ shock reservoir made the nitrogen valve vulnerable to damage. He designed a bladder cap that was less vulnerable to damage in a crash (and it holds a larger volume of nitrogen).

Going even further in the same direction, the forks were stiffened so they would ride higher in their stroke. Surprisingly, this made them feel plusher. The fork action was very smooth.

Pro Circuit race mechanic Damon Conkright, who worked with Josh Hansen this past Supercross season, handled many of the engine duties. When Pro Circuit develops a bike, one of their guidelines is to put the same amount of development time into each bike so that their package is competitive and equal. They don’t make one bike better because they sell more or because their race team rides that brand.

The project engine was fully massaged with a high-compression piston and head porting by Mitch Payton himself, and the compression was upped even further by flat-faced valves. Surprisingly, our project bike still didn’t need race gas. Damon is also quick to point out that Pro Circuit’s camshafts for the 2010 YZ450F don’t require purchasing valve springs. Instead, the cams come with spring seats that change the preload on the stock springs. Pro Circuit’s 2010 YZ450F cam design is mainly for the top-end, but there’s a small improvement from low-to-mid as well.

Unfortunately, our project bike didn’t receive Pro Circuit’s coated tappets. Giving the buckets a

Diamond-Like Coating (DLC) minimizes wear of the cam lobes and buckets. This is a good mod for long-term durability.

With all the internal engine parts handled, the final touches were a Ti-4R exhaust and a high-pressure radiator cap. Pro Circuit mapped the bike on the dyno using the Yamaha GYTR Power Tuner. After all the hours of development, all that was left was to grab a shopping cart and run down the aisles at Pro Circuit with arms extended to sweep up trick parts.


“The Pro Circuit bike had the best YZ450F powerband of the group. This was a surprise, because at no time did it feel like the most powerful engine. It was a great engine, but not by virtue of hitting hard. Instead, it had smooth delivery that was available whenever you needed it. The bike was hooked up everywhere with no dips or letdowns.”
“I could go faster on the Pro Circuit YZ450F than on any other bike in this test. It was easy to ride. The power delivery was broad and smooth. I could ride it effectively at almost any rpm.”

“Altogether, the Pro Circuit YZ450F may not have made the most peak horsepower (at least by a seat-of-the-pants test), but it had the fastest overall powerband. It revved faster than any other bike, which allowed you to get the most out of each gear quickly. Plus, it didn’t scare you off idle. It was smooth and offered the most controllable roll-on power. Best of all, it didn’t stop pulling until it hit the rev limiter.

“When I first rode the Pro Circuit YZ450F in practice, I thought it was slower than the other YZ450Fs. But in the first moto, I found myself railing corners without any fear of the bike bucking or jolting me around. It allowed me to go fast?faster than I could ever go on the stocker. This engine gave up power that it didn’t need (down low) and added it where it did need it (on top).”
“The longer shock linkage was the most noticeable improvement on the bike. Every test rider would come in from a test session and claim that this YZ450F handled better than the other YZ450Fs. The Pro Circuit linkage brought the bike into better balance.”
“The first thing I noticed on the track was that this bike was lower than a stock YZ450F. It didn’t have the goofy twitch on the entrance to the turns. You could drive it in without having to make any snap corrections.”

“The forks were really good, but we had some issues with the shock.”

“I had no issues with the Pro Circuit forks. They stayed high in their stroke and always had ample travel left to handle any size bump. The shock was dead feeling and had too much rebound damping. It didn’t reload as fast as I would have liked.”
“Overall, the Pro Circuit engine mods matched all the rest of the parts to perfection. The power delivery was very un-Yamaha-like, which I liked.”


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