December 28, 2007

Horsepower Myths



Discovering the truth

(ED—We asked the guys at Speedwerx if they could dispel some common myths about horsepower that circulate in the snowmobile industry. We’ve broken it down into categories and then present the myth and Speedwerx answers.)

 

Pipes (single or twin pipes)

 

Myth: Most horsepower on the dyno makes it the best pipe.

 

Dyno numbers can be misleading in more ways than one. For instance, some aftermarket companies will dyno the engine at lower temps to show their product is producing more horsepower than it actually is. A cool motor with a hot pipe is a very easy way to show a gain in horsepower. When this happens it not only hurts the customer, it hurts the entire industry because the customer will think that all aftermarket products and companies are created equal and that is not the case at all.

The other way they can be misleading is, even if they are dynoed at a running temp you would be operating at in the real world, the pipe or pipes may have a really peaky or narrow powerband. This makes your machine more sensitive to changes in snow conditions, elevation, air temperature, you name it. When this happens it can be a tuner’s nightmare because changes are required in the clutching, jetting and/or fuel delivery areas.

Some pipes may only make power for one 10 second blast on the dyno, where in the field you are wide open for several seconds, maybe even minutes, at a time, depending on your riding area.

We're not saying a product cannot be developed on a dyno nor are we saying that all dyno sheets are false, but these are very important things to pay attention to. The easiest way to discover which product may or may not be best for you is to ride it and see it perform in the real world instead of on a piece of paper.

 

Canisters/Silencers/Mufflers (on single pipes for consumer use)

 

Myth: Less pressure, less restrictive and louder equals more power.

 

Two-stroke exhaust systems are very sensitive to pressure. Too much pressure can cause engine failure or a loss in performance. Not enough pressure can cause a loss in performance as well.

Louder systems do not make more power than quieter systems. Louder ones may feel faster due to the noise level but more often than not a quieter system will perform just as well as, if not better than, a loud system on consumer single pipe applications. You may ask, "Why don't race sleds have a quiet exhaust system?" It's because the entire system on a full race machine is designed to work with an open stinger and/or glass pack silencer assembly to save weight and room. Also, if we ran open stingers on all the sleds we ride off the race track, we wouldn't have anywhere to ride due to people complaining about the noise.

With enough testing a quiet exhaust system can make just as much or more horsepower than a loud system.

 

Clutching

 

Myth: You need a $300 set of clutch weights to make your drive clutch upshift harder.

 

In most cases you can achieve the same harder upshift with a couple of $2 spyder washers. Adding washers behind your spyder will let the clutch weight stand up more at clutch engagement, thereby allowing more belt squeeze and quicker upshift. It will also lower your engagement rpm, so you may need to go with a stiffer drive spring or notched weights.

 

Cylinder Heads—Inserts vs. Stock Head Mods

 

Myth: All cylinder head upgrades are the same ("compression is compression").

 

More times than not, a billet dome or head insert will produce more power and better performance than a stock head with .010 or .020 of an inch removed from the base by your buddy down the street. There is way more to a head upgrade than what the compression ratio is or what it has for cranking compression. We look at squish band angle, squish band width, pocket radius, pocket depth and squish velocity when designing a new head. When a stock part is modified, it is very hard to change any of these areas to what you exactly want due to the amount of material in the casting in stock form.

More compression is not always better. Too much compression can cause engine damage or failure. If heads are tested and designed properly, the manufacturer will (or should) have a suggested operating range for that part. See Figure 1.

 

Air Intake Systems

 

Myth: Bigger opening equals more power.

 

More air or a bigger opening is not always better. Many times it can be, but we have seen cases where certain sleds do not like a wide open intake system, even when jetted and set up properly. A bigger hole will have less velocity or draw than a small hole and vice-versa.  This can have a huge effect on your machine's performance. Finding the happy medium is most important. When ordering an intake system, ask the manufacturer which machines the system is designed for and what units they have tested it on as well. 

 

Race Gas Or Higher Octane Gas

 

Myth: Race gas or more octane is better.

 

Running race gas or higher octane gas on a machine that is intended to run pump fuel can be a waste of money and you could be making less horsepower than you would with a lower octane fuel. Race gas burns slower than pump gas most of time. Yes, your engine may run cooler with race gas, but you need to make some heat to generate horsepower. The manufacturer releases a suggested octane rating for your sled that you should run. If you add any performance parts and higher octane fuel is needed, the performance company or manufacturer should include that information in the instructions. It never hurts to ask if you are not sure.

 

(ED—Speedwerx is located in Forest Lake, MN. For more information, contact 651-982-6020.)







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