(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
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.
(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.
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.
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 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
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.
located in Forest Lake, MN. For more information, contact