Hunterworks on Top Speed, CVT Belts and Air Filters

| February 9, 2010 | 0 Comments

By Todd  Eldridge,

Hunterworks Race Yamaha Rhino

Hunterworks Race Yamaha Rhino

Just like most all tech articles I write, this one is inspired by you the end user. Tech articles are designed to inform a group of people who may not otherwise be savvy to what some would say is common sense. The wide majority of UTV owners are not experts in all things mechanical and that is fine, if you were, then what would be the point of tech articles? As I said this tech article is inspired by you, I get lots of phone calls more or less about the same things so I thought I would just share some common answers to common questions.

Top Speed and Acceleration:

Top speed has so many variables that just doesn’t get thought about. One thing people don’t realize is when you get over 45 to 50 mph, then wind resistance plays such a large role. Windshields, roofs, back panels, light bars, long travel arms with the wheels sticking out past the body and believe it or not head rests all slow you down. On our race rhino a slim line roof cost me 3 mph on top speed so it is off now. On all brands of UTV’s a worn belt is big culprit. People say “My belt does not look worn”, most of the time you can’t tell it is worn because it wears thinner across it and it wears smooth. What happens is as it gets narrower and it will no longer ride as high in the primary sheaves as it once did and you lose top speed, you will also hit your rev limiter sooner too. On a Rhino dirt builds up in the grease in the primary sheave and does not allow the roller weights to roll out as far as they used to, then the belt does not go all the way up like a worn belt and top speeds come down and rpm goes up. On Teryx’s and RZR’s the belts also stretch then the belt needs adjustment to get it back in spec. Rhino owners don’t have a adjustment but they don’t need one.

Something to look for on the engine is checking to see if your throttle is opening all the way. Had a good many customers whose throttle was out of adjustment on their Rhino and they didn’t know it until they bought a ignition to get by their rev limiter. Three quarters throttle will get you to 41 mph where the limiter kicks in but won’t get you much above that when you get by the rev limiter. A simple valve adjustment can help too, if the valves are not opening enough then performance goes down.

Tires are probably the biggest culprit of top speed and acceleration. Large diameter and heavy tires will simply drag you down. Some people think larger tires should make them go faster and that is true if you have enough power to turn them but most don’t. Taller tires change the final gear ratio and the heavy mass needs much more power to turn them. Once I dynoed a set of 26x11x14 popular brand tire to see what the loss was and I lost 4 HP and that was just on the rear wheels. Got to thinking later, you gotta push the front heavier tires too so I might have lost 6 to 8 HP. Example: Recently we did a cam and exhaust install on a 700 rhino that had stock tires, it would hit 62 mph and the raised rev limiter in about a 1/8 of a mile, changed over to his larger heavier tires and at 1/4 mile we topped out at 60, it felt like it had drag chute on it. My recommendation is to purchase a set of light tires and try hard to not go over 27″ I personally use 25″ tires. I won’t talk about brands here but there is a good light tire for mud and a good light tire for all terrain.

Prolonging CVT Belt Life:

How you drive is very important on the fly weight style clutch found on a Kawasski Teryx or Polaris RZR. Probably the worst thing you can do is ease on the gas and take off very slowly. Why? Because at idle the primary sheave is spinning and the belt is not moving, as you rev the engine up the primary sheave slowly closes onto the belt and starts your movement. If you ease on it then you are slipping your belt and over time you will wear it out. Best bet is to gas and go, I don’t mean take off with the tires spinning I mean just step on the gas and go. Rhino’s don’t have this issue since they have a roller weight style clutch with a wet centrifugal clutch internal to the engine and the belt is in constant tension. I am personally against clutch kits as a general rule in a Rhino but on the Teryx and RZR I think they make a big difference. For one, they make for more of a positive belt engagement and two they really put the power to the ground quicker due to the change in shape of the fly weights. I prefer the adjustable type clutch kits for the Teryx and RZR over a kit that is made for one purpose because if you change something on engine or go with very large tires you will need to make a change in your clutch then you have to go buy another one so the adjustable is simply a better value.

Another thing that has been real popular is a CVT filter. I used to think this was a good idea to keep dust out, but have decided that the dust is much less of a culprit than the increase in heat caused by the restriction a dirty filter causes. If you must use a CVT filter then please do NOT use oil on it and wash it daily. While on the heat issue I got a call the other day about having flat spots on some roller weights on a Rhino. He thought the weights were the culprit but after investigation I found out he had a machined sheave that had too material removed causing his belt to ride too high causing it to slip creating heat then he had also snorkeled his CVT with some 1 1/2″ pipe, it simply was not getting enough air to keep it cool. Remember this fact, a 4″ pipe flows 4X the amount of air a 2″ pipe does. Increasing or decreasing the diameter of any opening by half does not reduce or increase by a multiple of two but four. Don’t believe me, figure out the area of a circle that is 4″ and then a 2″ and you will find the area in the 2″ is four times as small. Enough with the flow measurements and geometry, point is don’t restrict the air going in and out of your CVT.

Protecting Your Engine:

I am personally against any brand of cotton gauze air filter, while I believe paper is the best at stopping dust it does not work well on a vehicle that gets wet, this leaves foam. Almost all the manufactures of off road vehicles use foam and they use it for a reason, it works. I prefer the oiled dual density style that has a open cell foam on the outside and closed cell on the inside. I have a picture somewhere of a cotton gauze filter that was ran on a Rhino for 250 miles and it had about 1/32″ of dirt inside filter and it was oiled properly plus we have had a good many customers who have had to have their top ends rebuilt due to dust getting by the filter and wearing the rings and cylinder out. Lots of people will say “well I use a outer wear on my cotton gauze filter”, it only stops the chunks and stops water from entering it does nothing for the fine dust. If you can see light thru a filter then dust will go through it.

Ever since the Teryx came out it has had a intermittent problem of blowing smoke out the exhaust normally after a high speed run. The addition of a aftermarket ignition or CDI as most call it worsens the problem. The cause of this is the breather tube inside the engine that runs to the bottom of the engine where it sits in the engine oil. Any engine blow-by or the air that moves in and out of the engine goes through this tube and then into the air box, since the air has to be pushed through the oil, high RPM will push oil into the air box. My understanding the reason for this tube sitting in the oil is to catch vapors and lock them in the oil and not allow them to be released into the atmosphere but what about all that oil smoke once it reaches the airbox and gets burned in the engine? The issue was addressed on the 09 model but was not fixed. Like others we came up with a fix by adding another vent to the engine and a catch can of sorts, we call it our STOP kit which stands for Stop The Oil Problem. There are a number of these types of kits available, some work fine, some don’t and lots of homemade fixes too. This issue is normal and there is nothing you can get done under warranty, it is simply a design flaw in my opinion that can be fixed by the aftermarket.

The issues mentioned are just a handful issues that we get lots of calls on and thought we would spread the word. Part of any off-road sport is tinkering on your vehicle and modifying it to meet your use and style. Weird as it may sound I like running into issues, it gives me the opportunity to learn something new and pass it on to someone else that might be having the same trouble.

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