The guys at Mototassinari have been helping two-strokes breathe better for years with their VForce reeds and reed block, and now they’re tackling four stroke intakes with a very unique approach to dirt bikes – swappable velocity stacks in the airboot. The Air4orce for the fuel injected 2011 CRF250R came in along with a series of rain storms, so I’ve only got one day on the mod but it’s pretty unique.The Air4orce is a new airboot that attaches to your stock airbox. Installation of the actual Air4orce is a snap, but getting the FI sensors unplugged and the subframe off the bike will take a little time.The new air boot comes with two velocity stacks to pick your power preference. They are essentially nearly-cylindrical air passageways for the air to route through after it’s passed through the air filter. The longer velocity stack is clamed to boost low end power, the shorter gives more in the higher revs. It’s actually a really cool concept and a place to gain and tune performance you probably wouldn’t think to go to, but the MotoTas guys did. The two different velocity stacks are easily swappable in and out of the air boot, and their sealing design is well thought out.I’d planned to first install the longer velocity stack, but after pulling apart the stock system the set-up looked very similar to what Honda has in there already. I wanted to feel more of a difference, so I went with the shorter velocity stack for my initial ride.
I’d describe the performance change as similar to a pipe that speeds up the revs down low – which is exactly the change I want to make with any 250F I ride. You know, keep the nice, smooth, predictable power of a four-stroke but spice it up with a little more willingness to rev. The top end power velocity stack did the trick, and the bike was more responsive and quicker to rev, which makes the bike respond better, act more nimble, and even feel lighter. Just like a pipe change that gives this same effect, the power felt a little ‘looser.’ It’s like the bike is racing through the lower rpm to do its work up top. But I live down low in the revs, and this set up works out great to have more immediate response (not to the throttle input, to the motor spooling up) in the low to mid rev range.One problem I encountered was a reluctance of the bike to fire up in the morning, almost as if the FI was rejecting the donor part. But I like what the mod has done to the power, and I’m going to play with the low-end setting soon. The best part is the kit comes with both velocity stacks, so a pipe swap now would give me two options to try with that mod.I’ll admit a pipe swap is easier and takes less time, but is more expensive (the Air4orce is listed at $298.00), and all that pipe investment is hanging out there just waiting to get damaged in a crash or from some nasty roost or trail obstacles. The Air4orce is tucked nicely away, is well built, and adds two state-of-tune options to any other mod you do to your engine… Well, only two for now. The MotoTas website promises more velocity stacks to come as they test with some of the top race teams.Want to learn more? So do I, so I’m gonna get some more time in with this thing for a more thorough write up for the magazine. You can check out more product details at www.mototassinari.com, or give those guys a call at 603.298.6646.