Greg, This sounds like a great idea,,but...there's always a "but" lol....I'm no hp expert but, i would think the easier the flow the more hp....but what about filtration??? you can run a velocity stack and get great numbers but the motor won't last....we know the K&N is trash for filtering silt and the UMP and DF work great...so, that being said, I would think the bigger DF is the best for filtration and flow (closed canister) and the smaller UMP would fall into second....$500 vs $300... here is a letter i got explaining "why" df-ump style flows more than a K&N whe both are dirty...
You are right about UMP not wanting to quote flow numbers as that is not how we test our kits and they don't really mean anything unless they are less than what the motor needs as I will explain. Simple math from a widely available equation based on engine size, RPM and efficiency shows that the RZR motor will only flow about 75 CFM at 6500rpm (85% efficiency), about 80 CFM at 7000 if you have a chip in it (again 85% efficiency). Please note that 85% is on the high side, most list 75 to 80% when doing the math. VERY few engines approach 100% efficiency and those are highly tuned race motors that are designed for a very narrow power band like for drag racing. When you guys put on a pipe and change the ignition and fuel settings from stock you are changing the 85% number to maybe 88%, not a huge change to flow. Turbos are another story as you are pressurizing the engine and flow rate is based on how much boost you run and they can go as high as 150%, that is why we do a larger canister for the turbo RZR. These other filter guys that say "flows 54% more than stock" are just pulling your leg, the motor won't flow that much anyway so that means they just have more holes in them to let more dirt through. If "more flow than stock" meant something then taking the air filter off would mean you would make unlimited horsepower right? No, wrong, any more than what the motor needs does not change the power it makes as the airflow is determined by the size, RPM and efficiency of an engine. While the stock RZR air filter has many problems in regards to dust retention, it flows more than enough air (when clean!) to feed even a modified RZR motor. The only gain from flowing more is how long the service life of the filter is as it will take longer to get dirty enough to flow less than the motor needs. The problem with cleanable filters is how bad they filter dust at the beginning of their service life. Their claims' of high 90's dust retention are cumulative, meaning at the end of the test when they are all plugged up their rating goes up but at the beginning of the test they are really bad, we always ask if the cleanable filter guys dyno at the end of the day or race and then tell us how much power they make. Usually they don't know but can feel the loss in power. And all that dust that went through when the filter was clean is killing the motor so how much power does a dead motor make? The Donaldson filters we use are 99.9% efficient for dust retention and don't need a layer of dirt on them to protect your ride. Now, back to flow, we test right on the vehicle to measure vacuum the motor pulls right after the air filter with a very accurate gauge that measures inches of water. That senses how hard the engine has to pull through the filter to get the air it needs and since an engine is a pump, it is pulling the air through, it doesn't just fall in there. We saw on our test RZR about 9" with a stock filthy air cleaner, about 4" with a clean stock filter and about 1.5" with no filter at all. Our UMP kit measured 3" of water and the big difference is ours will stay there for much longer time since the filter is keeping clean as you go since 85% of the dust is spit out the little valve on the end cap. That means you are making good power for much longer service life of the element and the motor stays healthy ( Ours will get dirty to, just will take 3 or 4 times longer). Those guys that think you are making 2 or 3 more horsepower cause of the cleanable filter they put on need to tell us how much it costs to rebuild their engines after a season or so of eating dust and how much more it makes when it is all plugged up. And for those that have to know, based on other kits we have tested and comparable canisters filters ours will flow about 115 CFM at 6" of water, way more than the RZR motor flows. Sorry I got so wordy but it is not just a simple answer and can cost you guys a lot of dough if you are steered down the "flows more air means more power" path. For those that want to read more about filter testing, just Google "Spicer filter test", it is very informative about good paper filters verses cleanable filters.
Thanks,
Cliff Cappos
Unique Metal Products
