Carburetor DifferencesWe will discuss the two different style of carburetors: fixed jet style (Crankshop) and carburetors with no jets (Lectron). The scenario now will also move to a modified engine and high performance pipes.
The graph printed on the next page shows the difference between two different style carburetors as tuned on the same engine in an overlay fashion. A detailed comparative graph like this allows a racer or tuner to learn the personality of an engine and become more knowledgeable with the specific effects different components have on that engine, allowing more fine tuning to clutching and suspension.
The red line represents the engine finely tuned with Lectron 48mm Carburetors. The blue line shows results of the same engine tuned with 52mm Crankshop carburetors. Once again, this is not an article to present a comparison as to which carburetor is better, but to provide a tuner with information that is known, but not yet available in print, to be able to study.
Either one of these carburetors is capable of winning races and racers have had huge success building engines with both style carburetors. The information provided here is intended to provide some detailed, readable information and perhaps aid in making some decisions for proper clutch tuning as well as suspension tuning.
If you look at the red Lectron line you will see a more aggressive acceleration early in the run. The Crankshop carburetor shows a more gentle run into the powerband. This could be misconstrued by a rider, since the Lectron carburetor may feel faster, and in fact is driving the engine to accelerate harder. However, there are tuning parameters throughout the rest of the snowmobile that will need attention to take advantage and/or make the best of both style acceleration runs.
For instance, if your clutching is tuned to accept the Crankshop style acceleration run more aptly and transfer that particular power delivery to the racing surface more efficiently, then you might find that your 60 foot times are lower than if you had the quicker-hitting Lectrons installed.
The available traction will also influence this greatly and in each scenario it becomes a tuner's game. Although asphalt racing does provide a more consistent racing surface, it is feasible for someone to experience traction problems and spin the track if they try to jump out with too much power, too early off of the starting line.
It boils down to being able to tune what you have. More power is not always necessarily the answer if you cannot harness it and use it efficiently.
Know before you goBracket racing has allowed any racer to be competitive, but just as in the case where heads-up racing is conducted, it is important to be the first to the finish line. Intimate knowledge of your equipment is the most valuable asset you could have when making tuning decisions.
Professional racers know their equipment very well and have fine tuned their race sleds to provide a good and effective power delivery to the racing surface. The ultimate scenario would be to have your sled just on the verge of spinning the track- but not over that line, thereby getting as much forward momentum as possible for every inch the sled tries to move. Some people will find that they tune their sled's clutching and suspension in a way that allows them to use the more aggressive acceleration curve of the engine. There are a lot of ways to get "down to the other end" and knowing the personality of your race sled is very important.
Personal ExperienceBack in 1997 when I ran 9.000 I had tremendous working knowledge of what the sled wanted for the available traction at the various race tracks that I attended.
On the first run of the day, I decided to make a soft run by richening my Crankshop carburetors purposely to scrub power. This developed a modest acceleration rate which, coupled with an admittedly lazy stab into the throttle, netted a slow 1.45 60-foot time.
Before my next run, I noticed the track personnel spraying very liberal doses of traction compound to the track surface. I went to the starting line to study the track condition- there were "teeth" on the starting line! One could have easily left a shoe on the line simply by trying to walk! I stepped the power back up and introduced the more aggressive acceleration run. The result: a 1.18 60-foot time!
I believe that the sled would have bogged with the prior round's calibrations in it.
This article only touches on one of the ways to control some of the traction and acceleration viariables involved with asphalt racing. It is also a testimony to knowing what the sled needs to operate at maximum efficiency.
With the power some of the top snowmobile engine builders are finding today, it is conceivable that we may soon experience what Top Fuel and Nitro Funny Car crew chiefs are experiencing- too much power on hand. The cars, and soon sleds, could overpower the race track at any time.
I am an advocate of the Lectron carburetor and know how to make them work very well. But I also know plenty of racers who are winning races with Crankshop and other carburetors because they know the sled's reaction and personality well. It is indeed a chess game and getting as many variables working in your favor as possible will make for a successful racing venture. This kind of information graph is only a small piece of the total equation, but if it helps a racer reach lower ETs, then carb tuning is one more variable that they have working in their favor.
Freddie Klies is the owner of Eastern Cycle Performance in Waterbury, Connecticut where the company's services are high performance engine building, dyno tuning and suspension and chassis building for motorcycles and snowmobiles. The company's website is at www.easterncycleperf.com.