Hunting for Horsepower
Aug 16, 2006
How Much Bang Do You Get For Your Buck?
When it comes to motor modifications, is it better to bolt on a few aftermarket parts or go with a fire-breathing Stage Three full-blown race engine? What does bolting on a pipe, filter, and jet kit get you compared to the expense and performance gain of a total race engine? Take a look at how much horsepower you get for your money. The results might surprise you.
Stage One:
The basic performance hop-up starts with enhancing flow in and out of your quad's engine (we used a Suzuki LT-R450 in this test). This is accomplished by improving intake and exhaust gas movement. Simply removing your quad's airbox lid and bolting on an aftermarket filter can increase flow and boost performance significantly. Adjusting the jetting or EFI settings will give your ATV more grunt, too. Adding an aftermarket exhaust system will boost performance as well as save a lot of weight, but the downside is cost and increased sound. These three key modifications are the foundations for increased flow and horsepower.
Aftermarket Exhaust
Aftermarket pipes flow more exhaust and can be much lighter than stock. Lightweight aluminum and titanium pipes typically weigh in the seven to eight-pound range. Power increases vary, but the increases are usually pretty healthy. Sound can be an issue as with most aftermarket pipes built to AMA specs-they sound in at around 101dB. Be sure to use a noise-reducing insert if you ride off-road with one of these pipes!
Air Filter
Aftermarket air filters like Uni, BMC, K&N, and many others are designed to flow more air, while at the same time keeping crud out of your quad's engine. Increased intake airflow is a key factor in producing four-stroke horsepower. Removing the airbox cover (in dry conditions) is another good way to increase ponies. Note: a jet kit or EFI adjuster should be used when removing the air box lid or adding an aftermarket filter. Alterations to stock air/fuel ratio must be compensated for.
Jet Kit or EFI Kit
Jet kits (carbureted quads), and EFI kits (fuel-injected quads) are mandatory when you modify the exhaust and intake. As the engine's airflow increases, so must the supply of fuel. For older quads there are numerous jet kits on the market. For modern sport quads like the Suzuki LT-R450 or Yamaha Raptor 700R, fuel injection mapping devices are available from Yoshimura, Dynojet, and others.
Conclusion
For the average rider or entry-level racer looking for more power, the Stage One upgrades are all they'll need. If you are racing and not consistently winning the C class, go Stage One and spend your extra money on suspension. If you are an aggressive B-class rider or an A rider, move on up to Stage Two.
Stage One (baseline 41 horsepower)
Yoshimura Stainless complete exhaust system
BMC Air Filter Kit
Yoshimura CMBR Cherry Bomb ignition/mapping unit
Total Price: $680.90 yields 6 horsepower gain = $14.49 per horsepower
Stage Two:
The next step up from Stage One is to improve the ignition curve and bolting in some hotter cams. Aftermarket engine cams provide for higher lift and increased duration over stock. This, in combination with a good valve job, hotter ignition, and the Stage One modifications, is another step toward horsepower nirvana. Aftermarket ignitions (black boxes) will give your quad an ignition curve that features higher RPM limits and a fatter spark. With the motor inducting more air (filter, airbox lid removal), and a better-sealed combustion chamber (valve job), the combustion chamber is charged more efficiently and evacuates spent gases faster (cams and pipe).
Ignition
Ignitions are very tricky. Your quad comes from the factory with a preset rev limiter that helps ensure a good balance of durability and performance. Once you start to build for maximum performance, you will need to increase RPM and manipulate ignition curves. But be careful! Go over the line, and you can float valves and even suffer CEF (Catastrophic Engine Failure).
Camshafts
Camshafts are the heart of a good racing engine. They come in either billet or reground styles. Billet is better, as it is generally harder and will retain its profile over hard use and time. The cams control how the engine valves open and close and are absolutely critical to high performance. Like most engine components, builders search for the fine line between performance and durability with cams. Note: shimming or replacement of the valve springs may be necessary with the use of aftermarket camshafts.
Cams
Cam Timing is an art probably best left to professional tuners. You can have the best set of cams installed in your quad, but you won't achieve optimal performance if they are not timed properly. Make a mistake, and you can bend a valve or worse-CEF! But find the sweet spot and look out: serious horsepower! Note: cams with adjustable cam sprockets make this job much easier.
Conclusion
This is a pretty serious engine. It has a good balance of reliability vs. performance. It delivers a noticeable increase in power over Stage One. For the semi-serious racer, this is the way to go. Service this engine properly and you will get long life out of it and a lot of wins.
Stage Two
Stage One +
Yoshimura billet cam set
Yoshimura titanium valve spring kit
Yoshimura cam timing
Total Price- $2,590.90 yields 9 horsepower gain = $51.82 per horsepower
Stage Three:
Beyond Stages One and Two are special gaskets designed to up compression-exotic high-compression piston and rings installed for more "bark" and lighter weight, the cylinder head is ported to maximize flow, and custom valves, cotters, and valve springs are fitted in the head. The bottom end of the engine is blueprinted, too. Every piece that rubs up against another piece (reciprocating mass) is carefully matched and polished. The crank is trued and balanced. Often the engine is treated with special anti-friction reducing finishes. With this much power, the clutch is modified or replaced with a quality aftermarket piece.
Head Porting
With the addition of more compression and a hotter cam, porting becomes necessary to evacuate the increased intake pressure after combustion. Although the stock castings are so good these days from the factories, porting is still needed to maintain the proper pressure ratio. But an artful port job from a skilled technician will yield more power and an overall stronger running engine. With the close tolerances of modern racing engines, it is important to have this work done only by very reputable shops with a long history and good reputation. Do your research!
Blueprinting
Blueprinting is one of the most overlooked but most important aspects of building a Stage-Three engine. "pro" engines are really powerful, but they are also smooth as silk. The reason is that every mating part has been massaged to reduce friction and enhance the engine's ability to produce power. If you gain 1/8th of a horsepower by polishing and mating 16 different internal parts, that adds up to a two horsepower gain. NASCAR teams spend $200,000.00 for two horsepower!
Compression
Compression is power, but too much compression is an explosion! Virtually all high-performance engines run high compression. Lighter pistons with different shapes, machining of head surfaces, and "kit part" gaskets help generate compression. With the increase in compression is a decrease in durability. Rings, valves, pistons, and cranks all take a beating by the increase in pressure. The rider takes a lot of checkered flags, though!
Conclusion
These are full-on racing engines. They need to be taken apart and inspected at frequent intervals; failure to do so will result in CEF. If you are a pro rider, failure to have this engine will result in LTC (Last to Checkers). Pay your money but do the maintenance. A holeshot is a wonderful thing!
Stage-Three
Stage One +
Stage Two +
CP Billet Piston
Complete Hinson Clutch
Blueprint and treat bottom end
Balance crank
Porting/machine work
Serdi valve job
Total Price- $4,895.90 yields 13 horsepower gain = $90.66 per horsepower
Overall conclusions:
Four-stoke racing engines are the ultimate study in incrementalism. Initially, a few broad-brush moves will yield big gains in power (Stage One), but after that, power and cost go up at opposite ends of the scale. Each horsepower starts to cost more, reliability goes down, and service intervals become more frequent. The Yoshimura motor tested here represents their three basic platforms for performance enhancement. The motors they build for pro riders Doug Gust and Jeremiah Jones are a lot more aggressive. All of the top motocross racers tear their motors down after every race-keep that in mind. Our conclusion is that you have to work within a realistic budget when it comes to power. If you are on a shoestring, throw a pipe on it and call it good. If you have the money, or the need for speed, dig out your wallet!
Our Test:
Here is how we did it.
Yoshimura runs the Suzuki factory race team of Doug Gust and Jeremiah Jones. Yoshimura has been building four-stroke racing engines for 52 years, so we figured they would be a good place to test. All tests were performed at their state-of-the-art racing facility in Chino, California. The bike used was a 2006 Suzuki QuadRacer LT-R450.
Yoshimura technicians Satoshi Momma, (Off-Road Racing Engine Development Manager) and Ryan Cox, (Jeremiah Jones' mechanic and Suzuki team engine guru) built and tested the engines for this article. Although Yoshimura has nine different dyno-rooms, we only used one. All tests were performed on a Dyno Jet ATV Dyno.
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10 Hidden Horsepower Secrets
Think you know all there is when it comes to finding hidden horsepower? Think again!
1. REM ISF (Isotropic Surface Finish) chemical treatment is a good way to increase horsepower, lower temperatures, and increase durability. There are several other friction-reducing surface coatings and treatments that have merit.
2. Pay close attention to service intervals. Yoshimura spells out service life limits of engine components in hours. They recommend that any Stage-Three engine uses an hour meter and that the service guidelines are adhered to strictly. Proper sealing in the combustion chamber is critical to making power. Not only does lack of maintenance diminish the pressure, but it can also lead to CEF. Those are three letters you won't like!
3. A clean air filter makes a huge difference. We have seen a lot of racers go two races (four motos plus practices) without changing their filters!
4. Fresh fuel is important. Do not store race gas for long periods of time. Also, on race day, store your fuel in a cool, dark place. It really helps.
5. Air leaks kill power. Make sure that if your quad has any o-ring seals in the exhaust system that they are all in good order. If your quad is backfiring a lot on deceleration, check for exhaust-system air leaks.
6. Drivetrain maintenance is a must for making power. A filthy swingarm pivot, worn chain and sprockets, and dry, bent axles will kill horsepower. Everything needs to move freely.
7. Weight is power. Coming off the gate, seven pounds is equal to roughly one horsepower. A really easy way to make your quad faster is to lighten the load. Of course, if you make it too light, it won't be safe, so use common sense. Maybe eat fewer doughnuts in the morning!
8. Make sure the brakes are adjusted properly and are not dragging. A dragging brake pad can really eat up power. Make sure that the rotors are not bent and that the wheels are aligned properly, too.
9. On any modified motor, make sure to check valve adjustment at least every eight hours. Titanium valves especially tend to tighten up after eight hours. A tight valve may not close all the way, thus you will lose compression and power. A sign that your valves are getting tight is a hard-starting quad.
10. The cam chain is very important. When the chain gets old, it stretches and gets loose. On a modified motor, make sure to check tension every four hours. On a quad with a modified engine and an automatic cam chain tensioner, it's a good idea to just replace the cam chain every 15 hours. If a cam chain is stretched, the entire cam timing of the quad is off. A sign of a loose cam chain is a ticking noise in the top end.