Pro Circuit RM-Z250 T-4 GP System

INSIDE THE PRO CIRCUIT T-4 GP RM-Z250 PIPE

WHAT IS IT? The Suzuki RM-Z250 (2007, 2008 and 2009) has a potent low-to-mid powerband. The Pro Circuit T-4 GP pipe makes it more of a mid-and-up engine.

WHAT’S IT COST? $749.95 T-4 (stainless), $899.95 Ti-4 (titanium)—            (951) 738-8050      .

WHAT’S IT DO? Team Suzuki rider Ryan Dungey runs a Pro Circuit pipe on his works Suzuki RM-Z250. When a factory team chooses to use off-the-shelf pipes from an aftermarket supplier, that is a strong endorsement—strong enough for the MXA wrecking crew to order a Pro Circuit T-4 GP system for our 2008 Suzuki RM-Z250.

WHAT STANDS OUT? Here’s a list of things that stand out with Pro Circuit’s Suzuki RM-Z250 Ti-4 GP System.

   (1) Performance. No other 250 four-stroke is as good off the bottom as the RM-Z250. The RM-Z250 bursts out of corners and pulls hard through the midrange. If the RM-Z250 has a flaw, it is that the engine hangs and flattens out from 10,000 to 12,000 rpm. It revs, but it doesn’t pull. Thankfully, the Pro Circuit T-4 GP system provides top-end in spades. This pipe makes the RM-Z250 a gear better in every situation. Corners that you were straining in second to get to can be rocketed into in third gear with the T-4 GP pipe. It adds a healthy dose of top end and doesn’t hurt the bottom-to-mid one iota.

   (2) Horsepower. From the very bottom to 7200 rpm, the Pro Circuit pipe and stock pipe are in a dead heat. From 7200 rpm on up to the 13,200 rpm rev limiter, the Pro Circuit pipe is one horsepower better. The peak power on the stocker is 35.9 horsepower, while peak on the Pro Circuit pipe is 36.9 ponies.

   (3) Torque. Pro Circuit’s torque curve is a match for its horsepower curve. Starting at 7200 rpm, the Pro Circuit pipe makes and keeps a one-half foot-pound advantage over the stocker.

   (4) Over-rev. The biggest weakness of the stock exhaust system is that it goes flat on the upper fringes of the rpm curve. In fact, there is a serious dip in the stock curve at 12,000 rpm (where horsepower drops off significantly). With the Pro Circuit pipe, the dip was erased and the top-end over-rev was significantly improved.

   (5) Fit. Pro Circuit uses the same style head pipe flange as Suzuki, but adds two springs for more security. We didn’t like the springs (since Suzuki didn’t need them). The rest of the pipe needs a little muscle to squeeze through the RM-Z’s Delta Box chassis.

   (6) Prices. Pro Circuit offers four versions of the RM-Z250 exhaust system. The titanium Ti-4 full system (head pipe and muffler) costs $899. The stainless steel T-4 full system retails for $749. The Ti-4 and T-4 have the exact same dimensions and performance; the extra $150 is for the lighter weight of the titanium. Additionally, the slip-on systems (without the head pipe) are available in both Ti ($525) and stainless ($425).

   (7) Place of Manufacture. Pro Circuit’s Ti-4 exhaust is manufactured in Corona, California.

WHAT’S THE SQUAWK? Apart from leaning out the fuel screw, we had no squawks. Given our druthers, we opt to run the stainless steel system instead of the titanium system. Why? They run the same, feel the same and we think that the stainless version is more durable. Not to mention much cheaper.

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MXA PRODUCT TEST: PRO CIRCUIT KX450F LINKAGE AND REVALVE

 

 WHAT IS IT? An aftermarket shock linkage and shock revalve for the 2006 Kawasaki KX450F that alters the rising rate, lowers the seat height and mitigates bottoming.

WHAT'S IT COST? $184.95 (linkage), $149.95 (shock revalve) and $7.95 (shock oil)            (951) 738-8050      .

www.procircuit.com

WHAT'S IT DO? Every MXA test rider has concerns about the rear suspension of the 2006 KX450F. In stock trim, it wallows (sways under acceleration), bottoms (so hard that it can break the rear fender) and pogos (bounces up and down on undulating terrain). Pro Circuit has a two-step plan to calm the rear of the KX450F.

Step one: A new set of strut arms were CNC-machined to lower the seat height and rotate the stock bell-crank into a firmer portion of its progression.

Step two: A totally revalved shock with vastly increased rebound damping (something the stock KX shock sorely needs) and a more progressive rate change to keep the shock from bottoming.

With the release of the all-new 2006 Kawasaki KX450F, Pro Circuit went to the mat to improve the KX450F's questionable suspension.

WHAT STANDS OUT? Here's a list of things that stand out with the Pro Circuit 2006 KX450F linkage and shock revalve.

(1) Performance. In the world of shock linkages, Pro Circuit knows what it is talking about. They make linkage systems for the KX125, KX250, KX250F and KX450F. The dog-bone used on the KX450F is a cheap and simple way to mitigate some of the KX450F's worst flaws (and Stewart uses it). Pro Circuit's linkage changes the leverage ratio to hold the KX450F shock higher in its stroke longer. In motion, it feels one spring rate stiffer throughout the stroke. By shortening the dog-bone from 132.5mm to 131.5mm, the Pro Circuit link lowers the rear of the KX by 7mm.

(2) Dual-action. Not a single MXA test rider liked the way the stock KX450F rear suspension felt. Initially, we tried a stiffer 5.7 kg/mm shock spring. This improved compression and lessened the wallow, but aggravated the rebound and didn't help bottoming control. Unfortunately, the Pro Circuit linkage only rotates the bell-crank enough to affect the first two-thirds (225mm) of the shock's travel. Even with the link, the KX450F will still be busy from mid-stroke on. The final solution must be found in the shock's valving. To that end, Pro Circuit's Bones Bacon revalved our shock to add needed rebound and stop the spike at the end of the stroke.

(3) Installation. The CNC-machined Pro Circuit linkage comes with the bearings and seals installed. All you have to do is replace the stocker.

WHAT'S THE SQUAWK? Kawasaki's engineers should take a look at what their race teams run so that the consumer doesn't have to make a rising rate change.

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