2003 Two-Stroke Exhaust Shootout - Bolt On Bonanza

The two-stroke engine is quite an amazing creature in itself. This internal-combustion engine is technologically archaic with its oil-fuel lubrication system, reed intake and open exhaust port. But when it comes to building performance through the exhaust system, even Einstein would have pulled out his hair crunching the numbers to milk horsepower, torque and a usable power delivery from a piece of stamped, welded and hammered-on sheet metal. Just a few millimeters off one way or another, and a two-stroke exhaust is nothing but a pile of scrap metal.

There is a science to building and altering the power delivery in a two-stroke, and only a handful of companies dare to claim they can do it better than the multimillion-dollar motorcycle manufacturers. Stepping up to the challenge at this year's Dirt Rider two-stroke exhaust bonanza are Bill's, DEP, Doma, FMF, Pro Circuit and SRS.

In addition to the plethora of exhaust in this test, we matched each unit to the corresponding silencer mate. FMF delivered two models: the Shorty and Titanium II. The difference between these is the Titanium II is built with titanium end-caps and inlet pipe plus an anodized-aluminum canister. Performance between the two was nearly identical, although the Ti system is slightly lighter and looks trick.

Exhaust preference is quite subjective. Some like it on top, some on bottom--power delivery that is. Because of this, it's really important to define your needs before you go out and lay down greenbacks for a new exhaust. For this test, we rated each system compared to the stock power delivery using a letter grade. Each bike started from a baseline grade between C+ and B, even if it is underpowered or overpowered compared with other bikes in its class.

Lake Elsinore's MX track acted as our testing bed because it offers a fairly consistent blend of medium- to hard-pack soil throughout the day. An elaborate crew of 13 took part in our two-day ordeal. We teamed one pro/expert-level rider with one amateur-level rider to evaluate two of the 10 two-stroke motocross bikes in our test, not to mention the umpteen number of exhaust combinations. Testers included staffers Ken Faught, Karel Kramer and Jason Webb and contributing test riders Ty Keefe, Kris Keefer, Rich Truchinski, Joel Albrecht, Chris Neitzel and Victor Sheldon. Associate Editor Scott Hoffman received the job of deciphering the pages of chicken scratches to present the data here.

The following information provides the insight needed to determine which exhaust setup is best-suited for a particular rider's needs, wants and desires. No matter your forte--off-road, hare scrambles, motocross or enduro--the answers are here.

The Goods

BILL'S PIPE Bill's pipe ($198.50): Bill's offers its exhaust in two finishes: standard bare metal or nickel-plated. Silencer ($98.75): Aluminum canisters are standard with the Bill's silencer, while the end-caps and inlet pipe are plated mild steel.

DEP DEP exhausts originate from Europe and are bare steel with mild-steel silencers in aluminum canisters. The exhaust runs $199.95, the silencer $99.95.

DOMA Exhaust ($182 for 125s; $210 for 250s): Doma pipes are available plated for an additional charge of $20. Doma silencer ($88 for 125s; $99 for 250s): Stainless end-caps as well as the polished-aluminum canister are standard on the Doma silencer.

FMF Right from the start, FMF earned extra points for equipping each of its exhausts with O-rings in the exhaust flange right out of the box. During our testing, we found little or no performance differences between the Shorty silencer and the Titanium II. Although FMF offers a standard-length PowerCore II silencer, we were only presented with the Shorty and Titanium for this test.

Factory Fatty ($229.99-$249.99): Similar in design to the Fatty, the Factory is constructed from thinner-gauge material, is precision assembled with hand-pounded welds and remains unplated for that factory look.

Fatty ($179.99-$199.99): The Fatty is FMF's standard-issue pipe; it is only available with a plated finish.

Gnarly ($179.99-$199.99): The Gnarly is constructed from 18-gauge material (thicker compared to the Fatty) and aimed at off-road riders or those seeking more bottom power and torque. The Gnarly comes nickel-plated and is only available for 250cc models.

Rev ($179.99-$199.99): FMF targets the Rev for 125 riders looking for more top-end and overrev.

SST ($229.99-$249.99): This unit, which features a special machined stinger section, claims to offer the broadest power delivery of any system in the line.

Shorty silencer ($99.99): Unit comes with an aluminum canister and stainless inlet pipe and end-cap.

Titanium II silencer ($149.99): FMF's Titanium silencer is built with a titanium inlet pipe and end-cap with an anodized-aluminum canister.

PRO CIRCUIT Works/Platinum ($198.50): One design available in two styles, the pipe comes unplated (the Works) or plated (the Platinum). PC exhausts are always very well built with precision welding and craftsmanship. Factory Sound silencer ($112.50): PC's silencers house a round aluminum canister with stainless inlet pipes and end-caps.

SRS Exhaust ($200 for 125s; $220 for 250s): SRS is very heavy into building pistons, but the company also offers a limited number of very well-built exhausts. The SRS system wears a bare-metal finish. Carbon-fiber silencer ($140 for 125s; $160 for 250s): These silencers are by far the trickest-looking in the test. The carbon-fiber canister with aluminum end-caps and stainless inlet pipe and bracket are standard on the SRS.

Baseline: The stock power delivery is nothing to write home about. The engine revs but doesn't have the punch of some of its class cohorts. Several manufacturers couldn't participate in the test because they still did not have units ready due to continued development.

Bill's pipe and silencer Fit: D / Overall Rating: C+ Comments: Bill's lost half a grade point due to fit problems. The silencer would not index the exhaust pipe's adjoining cup, and we had to cut off the end of the silencer and sand its inside. The performance of the exhaust was a tad better than stock and offered a bit more usable and broader midrange. Bottom was about the same as stock, while the top fell somewhat short.

FMF Fatty with Ti II silencer Fit: A / Overall Rating: B+ Comments: One of the best FMF combos during our CR125R test. Bottom is about the same as stock but with a hint more mid. Pull from the mid to the top is healthier and allows the engine to rev harder into the top.

FMF Rev with Ti II silencer Fit: A / Overall Rating: B Comments: Based on its name, we weren't expecting any gains down low. The mid is a little meatier with a decent pull up top, but this system falls off a little on overrev. It is a little better than stock or the FMF SST combo.

FMF SST with Ti II silencer Fit: A / Overall Rating: B- Comments: The SST offers broader power with a little more bottom and midrange and about the same pull up top compared to stock. There was no defined area in the power curve that was noticeably enhanced, although it offered a broader power curve. This wasn't the best unit in the lot but was still slightly better than stock.

SRS exhaust and carbon-fiber silencer Fit: B+ / Overall Rating: B- Comments: The SRS combo is very similar to the Bill's system. Midrange delivery is stronger compared to stock, but the SRS set doesn't offer the broad power range of the FMF units. Some of the guys still claimed the SRS is the best-looking combo for the CR125R.

Baseline: The 250R's stock power curve is quite lackluster but easy to ride. Bottom-end is decent, with most of the power delivered through the mid. Top-end power and overrev are truly weak stock.

Bill's pipe and silencer Fit: B- / Overall Rating: B- Comments: It was a little difficult to fit the Bill's CR250R exhaust. Power delivery is very similar to stock with slight gains up top. This would be a great replacement for the stock exhaust.

Doma exhaust and silencer Fit: A / Overall Rating: A Comments: The CR250R surprise came in the form of the Doma exhaust combo. This is the one unit that boosted performance everywhere. Bottom is stronger, midrange is snappier and it actually pulled up top and revved. This was the class favorite during our test.

FMF Factory Fatty with Titanium II silencer Fit: A / Overall Rating: B Comments: The Factory Fatty feels almost identical to the standard Fatty. The pull is slightly broader in the mid compared to the Fatty. Power is delivered better than stock but is nothing to brag about.

FMF Fatty with Titanium II silencer Fit: A / Overall Rating: B Comments: The Fatty doesn't really stand out in any one area. Midrange is a little better than stock, but for the most part, bottom and top are nearly the same. This would make a great stock replacement with its minor improvements in the power delivery.

FMF Gnarly with Shorty silencer Fit: A / Overall Rating: B, B+ off-road Comments: Of the CR250R exhausts, the Gnarly is best-suited for those looking for an off-road-capable combo. Bottom is better than stock with a strong, very usable delivery in the mid. Top is a little weak, and overrev falls short. Power is very tractable and pulls out of corners a lot easier than stock.

FMF SST with Shorty silencer Fit: A / Overall Rating: B+ Comments: The SST offers a very broad power range across the board. We saw slight improvements in roll-on power, and it pulls a smidgen harder through the upper midrange. Top-end is very similar to stock. We were expecting more from the SST, but overall it is a decent combo.

Pro Circuit Works with Factory Sound silencer Fit: A / Overall Rating: B Comments: The PC setup looks sharp on the bike and offers decent improvements from bottom to mid. Top is a bit better than stock, but overrev still falls flat. Throttle response is snappier but doesn't really transform the CR into a monster. Testers commented the silencer sounded odd--as if the muffler packing was blown out even though the silencer was brand-new.

SRS exhaust and carbon-fiber silencer Fit: B+ / Overall Rating: B- Comments: When compared to stock, the SRS is very similar, offering minimal improvements throughout. Mid is a little stronger, but that is about it. The silencer is by far the best-looking of the bunch.

Baseline: The KX wasn't the fastest bike during our 2003 125 shootout, but it is still much improved compared with older models. The power is delivered fairly robustly in the mid with a usable top and overrev. There is no real fault with the performance--except it just needs more of it.

DEP exhaust Fit: B+ / Overall Rating: A- Comments: The DEP presents the best midrange power of any exhaust we bolted on the KX125. The power is crisp, starts very low in the rpm range and comes on very strong as the revs start to build. The meaty mid really yanks the bike from corners. The pull up top is decent, though not quite as healthy compared to the Pro Circuit system. The DEP was one of the top-performing units for the KX.

Doma exhaust Fit: B / Overall Rating: B Comments: The Doma presented more bottom and made the bike easier to ride lower in the rpm range. It performed better than stock as it pulled into the mid but robbed some power from the top and overrev. This is a good combination for beginner and/or novice riders or those who don't like to totally scream a 125.

FMF Factory Fatty with Titanium II silencer Fit: A / Overall Rating: A- Comments: The Factory Fatty performed quite a bit better than the standard Fatty on the KX125. Throttle response was snappier, and the delivery was improved from the bottom to the top. This combo pulled better coming out of corners and proved to be the best offered by FMF.

FMF Fatty with Titanium II silencer Fit: A / Overall Rating: B Comments: The Fatty took a little from the bottom and moved it into the midrange. The mid comes on with a harder hit and pulls slightly stronger going up top compared to stock.

FMF Rev with Titanium II silencer Fit: A / Overall Rating: B- Comments: On the KX125, the Rev just didn't live up to its name. Power delivery was decent with average top-end--but not the blistering mid and teeth-rattling top we were expecting. It still ran better than stock in several areas but ended in midpack among our test crew.

FMF SST with Titanium II silencer Fit: A / Overall Rating: B- Comments: The SST didn't have the midrange boost of the Fatty and some of the other units. Bottom was a little sluggish, and we felt a slight hesitation. Delivery from the mid to the top was a hair better than stock, but this system just didn't shine in any particular area. We did notice the engine detonated slightly under a load. Jetting for this combo may have been slightly off, but it did not come with suggested jetting settings.

Pro Circuit Works with Factory Sound silencer Fit: A / Overall Rating: A Comments: The PC furnished power all over the boards with this baby; let's just say we felt improvement throughout. The PC was rated as the best KX125 pipe and silencer.

Baseline: The 2003 KX is a brand-new ride and proved to be a great bike in stock form. The power provides torque but lacks that explosive feel. The KX needs more bottom power, a quicker-revving delivery with more punch, and more overrev to bring it up to par with the front-running 250s.

DEP pipe and silencer Fit: A / Overall Rating: B+ Comments: The DEP is a good combo that is smooth but snappier compared to the Doma. It builds its power a little faster but not quite as robustly when lined up against the FMF units tested. Bottom is really good, and the power carries on to the top with a usable overrev compared to the stock exhaust.

Doma pipe and silencer Fit: A / Overall Rating: B+ Comments: The Doma develops a lot of drive right off idle. The delivery is smooth, and it pulls really well while exiting corners. Once it enters the midrange, the power gains start to level off. Because of its great bottom you can feel the pull on the track. Up top the Doma starts to come alive again and wants to pull further than stock. Overall this is an easy-to-ride combo that works well for off-roaders and motocrossers seeking a smooth tractable delivery.

FMF Factory Fatty with Titanium II silencer Fit: A, B- for the Titanium II silencer Overall Rating: A Comments: The Factory Fatty is almost identical to the Fatty, but we did notice the Factory has a snappier throttle response and delivery. One of our three test riders rated this his favorite.

FMF Fatty with Titanium II silencer Fit: A, B- for silencer / Overall Rating: A Comments: The silencer lost points due to the fact the bolt holes didn't line up well with the subframe. Powerwise, the Fatty is a winner. Compared to stock the Fatty boasts power gains just off the bottom, pulls stronger in the mid and holds on all the way up into the top-end. Overrev is also improved. For off-road, we could have used a little more bottom.

FMF SST with Titanium II silencer Fit: A, B- for silencer Overall Rating: A Comments: The SST delivered the meat of its power from the lower bottom to the lower top. This is an excellent-performing combination that's fast and easy to ride. The rear starts to drive very low in the power range and makes for easy yet quick cornering. The bottom is good enough that it would make a excellent choice for trail riding as well as hard-core motocross. Two testers picked the SST as their exhaust of choice for the KX250.

Pro Circuit Works with Factory Sound silencer Fit: A / Overall Rating: B- Comments: The power is very tame and feels as if it lost torque in the process. Testers said the bike was loud and delivered the power flat. It builds some muscle on top, but it takes some clutch to get there. A few riders suggested the flat power may work off-road.

Baseline: The 125 SX is one fast bike in stock form, although its downfalls are that it lacks low, low bottom and a good overrev. These were two areas we were looking at for gains.

DEP pipe and silencer Fit: A / Overall Rating: B Comments: The fit of this pipe was a bit different. It wasn't bad, but the pipe tucks up and in much better so some of the mounts needed to be loosened and moved. The DEP came on sooner than any other pipe. It made the engine very torquey, so exiting tight turns was child's play. The hit in the low mid feels like a 250, but as it starts to rev, it drops like a sack of potatoes. If you like a hit and low to upper-mid power, this is a winner.

Doma pipe and silencer Fit: A / Overall Rating: A Comments: This European pipe has bottom that rivals the stock pipe's. The mid hit is perhaps a little more controllable, yet it still revs. It goes flat earlier than the KTM Racing Spec but will appeal to a wider range of riders. This pipe would work well at a variety of tracks and even off-road and was among the top three favorites during the KTM 125 test.

FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: A Comments: Almost identical to the Fatty although the Factory is slightly stronger in the mid, but just noticeably.

FMF Fatty with Shorty silencer Fit: A / Overall Rating: A Comments: Bottom-end is enhanced, and the usable pull through the mid is very defined. Up top it drops off a little early for some. High-revving pilots may want to look for another exhaust--this pipe likes to have it shifted in the meat. FMF SST with Shorty silencer Fit: A / Overall Rating: A Comments: The SST doesn't make a lot of power in one place or all at once but rather across the board. Aggressive riders may feel the engine revs a little slowly even though it pulls very strong throughout. This was another unit that was ranked in the top 25 percent during the KTM 125 test.

KTM Racing Spec Doma Fit: A / Overall Rating: B+ Comments: This Spec pipe available directly from KTM is weak down low and slightly off compared to stock. It builds ponies that rally the stock exhaust in the mid and starts to come alive when the rpm build; overrev is also better than stock. This is a setup for riders who like to twist the throttle wide open and leave it there.

Pro Circuit Works with Factory Sound silencer Fit: A, C+ for the silencer Overall Rating: B Comments: The fit of the exhaust was on the money, but it seemed as if the silencer's inlet pipe was too short and barely met up with the exhaust. The PC mimics the stock power curve with a stronger delivery down low. The mid is quite robust, although not as good as the Doma's. Up top it falls off like the stocker and requires a rider to hit his shift points.

Baseline: Lack of horsepower is not an issue with the 2003 250 SX; rather it's just how that power is delivered. Our gripe is the bike lacks bottom before it runs into its ultrapowerful delivery. Doma pipe and silencer Fit: A / Overall Rating: A

Comments: The Doma produces an amazing hit down low, but ironically it doesn't yank your arm from the socket. It puts the power to the ground and really transforms the stock delivery. The Doma, as well as every unit we tested, conveys a strong mid. Even the bottom delivery is to die for, while this system still wants to rev. Of the units we tested, this was the crowd favorite.

FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: A- Comments: On the track we felt the Factory Fatty performed identically to the standard Fatty, but this is not a bad thing.

FMF Fatty with Shorty silencer Fit: A- / Overall Rating: A- Comments: The fit is a little snug next to the cylinder, but the parts lined up just fine. The stocker is anemic down low; this is where we noticed the gains from the Fatty right off. The added bottom makes the KTM easier to ride. From that point on, the energy keeps going through the mid and into the top. This is one bike where you need to manage the power instead of concentrating it all in one place; FMF does a great job doing that.

FMF Gnarly with Shorty silencer Fit: A / Overall Rating: B- Comments: This pipe really is gnarly! It hits hard and early. It will pull gear taller than stock in every turn, but it's too violent for off-road. If you aren't an rpm guy, this is a good combo.

Baseline: It's hard to really pinpoint a shortcoming when talking about the RM125. As with any 125, though, we are always looking for more.

Bill's pipe and silencer Fit: A / Overall Rating: B+ Comments: Bill's knows the RM and is always a contender with this bike. Bottom mimics stock, while the mid comes on with some clout and pulls ultrastrong before falling off on top. This is a good setup, but it requires you to hit your shifts right on the money.

DEP pipe and silencer Fit: A / Overall Rating: A- Comments: Like the SST, the DEP system doesn't produce extra bottom but makes up for it as the ponies build in the mid. This is where the usable performance can be found. It takes the momentum from its strong mid and keeps it pulling into a very effective top and overrev. The DEP was among the three favorite choices in the test.

Doma pipe and silencer Fit: A / Overall Rating: A Comments: Like several units, the Doma makes the bulk of its delivery in and around the mid. The Doma earned high marks because of its power characteristics. It comes on slightly sooner than some of the other systems, yanks through the mid and has decent top. It makes good power and delivers it in a way to extend each gear and continue to pull. The Doma topped the podium at the end of the day.

FMF Factory Fatty with Titanium II silencer Fit: A / Overall Rating: B Comments: This was again almost identical to the FMF standard Fatty. Mid was slightly upped, while top and overrev were lacking.

FMF Fatty with Titanium II silencer Fit: A / Overall Rating: B Comments: FMF builds a quality product with the RM125 Fatty, though power output is not as good compared with other combos tested. Bottom was on par with stock, while the midrange punch is improved and allowed the bike to be ridden more aggressively coming out of corners. Top-end pull was weak and only slightly boosted over stock.

FMF Rev with Titanium II silencer Fit: A / Overall Rating: B Comments: Like some of the other units tested, the Rev churns out a bottom copied from stock, while most gains were centered in the mid. The Rev pulls harder than the Bill's up top but not quite as strongly compared to the FMF SST. The Rev finished around midpack during our test; good but not great.

FMF SST with Titanium II silencer Fit: B+ / Overall Rating: B+ Comments: Even the SST system doesn't pack in anything lower in the power curve but adds a serious punch over stock in the mid. The SST revs out further than the FMF Rev, Fatty or Bill's. As long as you don't let the revs drop, this setup pulls for days.

Pro Circuit Works with Factory Sound silencer Fit: A / Overall Rating: A Comments: PC did a great job with its RM125 exhaust. The power is very similar to the Doma's--great mid to top--with a crisp snap of the throttle. On and off the gas the PC is quick to respond and allows for fun in the entire usable power curve. The PC finished up on the leader board during this test and ended up as the system that went home with the bike.

Baseline: The RM250 is another bike that kicked it up a notch in 2003. The power release isn't really lacking in one particular area; it offers a crisp throttle and an overall ridable power curve. We were basically seeking an exhaust setup that would amplify the stock delivery.

Bill's exhaust and silencer Fit: A- / Overall Rating: B Comments: Since Bill's only runs one mount on its silencer, we would have liked the company to have provided a shorter bolt for the second mount/fender bracket. The power delivery of this pipe is quite robust in the mid but tends to fall off up top and lack a usable overrev. This is a system that works best for supercross-style or very tight courses. If you're a short-shift-style rider, the Bill's may work, but if you like to twist it to the moon, look elsewhere.

DEP pipe and silencer Fit: B / Overall Rating: B+ Comments: The silencer mounts were a little off but they didn't pose any huge problems. The DEP robs Peter to pay Paul slightly by snatching some bottom and moving the entire power curve to the right of the scale. After taking some bottom, the mid hits with some power and just wants to keep going and going. The delivery is smooth and very easy to ride as it revs out. This is a great all-around exhaust that is well suited for fast GP-style tracks or even desert riding.

FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Factory didn't prove to offer any measurable gains compared to the FMF standard Fatty. If anything, throttle response was slightly improved at best over the Fatty.

FMF Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Fatty dispenses gains over stock but not as meaningfully when lined up against the PC or SST. It's a well-rounded system but doesn't stand out in any single area.

FMF Gnarly with Shorty silencer Fit: A / Overall Rating: B- Comments: As a whole, the Gnarly is a little off-center. The output is somewhat flat and smooth for motocross and tends to fall off on top. This is a system that will shine off-road, however. The power feed should billy goat the bike around on the nastiest trails.

FMF SST with Shorty silencer Fit: A / Overall Rating: B+ Comments: The SST hit pay dirt with the RM250. This system enhances the bottom-end while building horsepower through a very usable and snappy mid. Up top the gains fall slightly but are still stronger than stock. The SST is a great moto exhaust and made the podium as one of the top three picks.

Pro Circuit Works with Factory Sound silencer Fit: A /Overall Rating: A Comments: The PC is a full-on moto setup that likes to be ridden hard and revved. The hit down low is better than stock but only slightly. After that point it builds its ponies rapidly and wants to rev. The hit is very punchy but rider-friendly at the same time. The PC combo turned out to be the number one choice.

Baseline: Stock, the YZ125 is a barn burner with some of the best power characteristics of any 125 ever produced. The power comes on early and runs all the way through to the top. More of what it already delivers is the target for the '03 YZ125.

Bill's pipe and silencer Fit: A / Overall Rating: B Comments: Bill's starts off by building more bottom and broadening the already-potent midrange. On top it is about the same as stock. The Bill's delivers moderate gains but enough to consider it better than stock.

DEP pipe and silencer Fit: B / Overall Rating: B+ Comments: Other than the fact the kickstarter hits the pipe, the DEP is a great overall addition to a YZ125. It outdoes stock down low, pulls longer in the mid and still wants to rev out on top. Although it wasn't our number one choice, it placed right there on the podium with several others.

Doma pipe and silencer Fit: B / Overall Rating: B Comments: The brackets on the exhaust and the silencer were slightly off, and it took a few extra minutes to get the system hooked up. The Doma is very similar to stock with about the same bottom, slightly wider mid and a little more overrev. This is a great replacement system that still adds some performance to the YZ125.

FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: A Comments: The Factory, like most of them, parallels the standard Fatty. Throttle response appeared a little crisper but didn't translate on the track. If you fancy the Fatty, you will adore the Factory Fatty.

FMF Fatty with Shorty silencer Fit: A / Overall Rating: A Comments: The Fatty produces a crisp throttle along the way to its award-winning enhanced mid. Up top the power keeps building and wants to rev further than stock and most of the other systems available. One of our two pro test riders marked this system as his favorite.

FMF Rev with PowerCore II silencer Fit: A / Overall Rating: B+ Comments: The Rev runs a little snappier compared to stock and supplied more mid along with a longer pull up top. It does rev further than stock, but we couldn't say it screams further than some of the competition. Overall it's healthier than stock.

FMF SST with Shorty silencer Fit: A / Overall Rating: B Comments: The SST tenders a broad power delivery but not quite as snappy or responsive when matched up to other leading units. The SST pulls stronger in the mid and on top over stock and seems best-suited for fast tracks.

Pro Circuit Works with Factory Sound silencer Fit: A / Overall Rating: A Comments: Picked as the head honcho by one tester, the PC comes to life from the first blip of the throttle. Bottom is superior overall and pulls harder while exiting corners. As the revs start to climb, it keeps pulling until screaming its brains out way up top.

Main jet 178 STD Needle-clip position STD-2nd STD Pilot jet 50 STD Air screw 1.0 1.0-1.25 Gearing 14/50 14/50-51

Baseline: The YZ250 engine is so fine stock it's hard to even think about improving it. But like most things in the world, more of a good thing is always well received.

Bill's pipe and silencer Fit: A- / Overall Rating: B Comments: The candidate from Bill's earned marks for its extra bottom-end and mid pull but lost some points for going flat a little sooner than stock; overrev was about the same.

DEP pipe and silencer Fit: B / Overall Rating: A Comments: DEP must have done its homework with this unit. The power comes on sooner than stock and extends out longer in the mid. With this setup you can shift early or come out of a corner in a higher gear and it will pull it. This gift keeps giving, stretches up top further than stock and holds its power longer before falling off.

Doma pipe and silencer Fit: B / Overall Rating: B- Comments: The Doma experienced gains down low at the expense of some top and overrev. If you're looking for some bottom, the Doma may be just what the doctor ordered, but our test riders were not about to give up top and overrev.

FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Factory pretty much mimics the Fatty to a T. On the track we were unable to notice any difference between the Factory and standard Fatty.

FMF Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Fatty is a well-rounded system but doesn't harvest gains like some of the other units. It pulls longer in the mid but about the same as stock down low and up top.

FMF Gnarly with Shorty silencer Fit: A / Overall Rating: B Comments: The Gnarly builds more punch down low and holds each gear further than stock going through the mid but signs off too soon. With its smooth deployment, the Gnarly is best-suited for those who torque a bike around the track or direct their riding more to off-road.

FMF SST with Shorty silencer Fit: A / Overall Rating: B Comments: With such a broad power delivery, the SST caters to several facets of riding. The mid is smooth and extends further than stock. This is a good all-around system and may even work well for GP and desert-style riding and racing.

Pro Circuit Works and Factory Sound silencer Fit: A / Overall Rating: B+ Comments: The PC picked up a little down low while retaining much of the stock curves through the midrange. However, the PC exhaust kept pulling up top and supplied more overrev and usable power along the way. The added delivery allowed riders to hold second and third gear longer before shifting.