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Roll_it_on

back fire screen

8 posts in this topic

I just purchased a uni filter for my BRP and I was wondering if the support cage supplied with the uni filter is sufficiant and if so can the stock filter screen be replaced without any ill effects. I guess I'm kinda wondering why Honda put the fine screen in behind the element if all it is supposed to do is support the foam and keep it in place :)

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Yes, the Uni Filter support cage is sufficient. I don't know the reason for the stock metal screen other than to support the stock filter and I've heard it's for backfire protection, but I'm not sure. In any case, I've been running the Uni Filter setup for over a year now, and there are no problems with it.

Of main importance is this; Is clean air getting to the engine? And as much as possible as quickly as possible? And is the exhaust exiting the engine as quickly as possible? With appropriate jetting and exhaust resonance at the correct rpm range to provide the desired power curve?

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There are plenty of people running with and without the backfire screen installed, but Uni told me to keep my backfire screen in. There have been a few people who have had their air filters catch on fire after their bike backfired and I read one account where an air box & side panel partially melted before the fire was put out, but this is far from being common even if your bike backfires. Some people remove one layer of the fine mesh screen so that’s it’s less restrictive while others buy an aftermarket backfire screen that’s less restrictive. A ways back I had my bike dyno’d with and without the backfire screen and I didn’t see enough of a repeatable difference to convince me that I’d gain much if anything by taking it out, so I left it in. The one thing that did make a noticeable & repeatable difference on the dyno was having the side panel cut out like team Honda. This mod increased the HP from ~4,250 RPM on up and improved the torque from ~3,750 RPM on up.

If I had built my bike with a different cam, exhaust system, porting, etc, so that the peak power was moved 1,500+ RPM higher up in the curve, then I’d probably take another look at the screen because it would become more restrictive as the engine RPM increases. A while back I read an interesting article about Johnny Campbell’s team Honda bike and here’s some text I copied and pasted from this very article regarding the backfire screen.

"An HRC Power-Up Kit (available through all Honda Dealers, Part Number 06130-NLB-010) is the star of this show, but many times the team will elect to use only a portion of the kit. The kit’s heavy-duty clutch springs, cam chain (plus corresponding sprockets and tensioner), high-performance cam and appropriate jetting (as well as additional breather holes in the airbox cover— though the stock filter and backfire screen are retained) are used for all events."

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Thanks guys for the responses. The idea of a side panel fire out on the back forty doesn't sound to appealing. I think I will just leave it in for the time being and perhaps experiment with opening up the air box :)

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Chances of a fire out the back forty are pretty slim and many guys could probably ride their bikes into the ground without ever experiencing this, but it has happened. It just depends if you're one of the few unlucky ones or not :)

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I have semi experimented with both removing a layer of screen and a modified 'cage' for my filter element. I felt that with the open cage (I haven't seen UNI's cage, I fabricated mine by using wire (aka coat hanger) pinched into the stock cage where the wire mesh is held with all of the mesh removed) you do not necessarily get a horsepower increase, but it did allow my BRP to rev faster into higher RPMs. The trade-off was a semi lack of throttle response at lower RPM due to volumetric 'inefficiences.' This is what the Team Honda 'Batwing' for the airbox cures. You can purchase this from Precision Concepts or fabricate one (that's what I did). This is a concept similar to a dual plane high rise manifold. I also noticed a slight increase in noise with the unrestricted cage. For me, the top end increases are worth every bit of money and time as I race National Hare & Hounds when I get the chance. My BRP also has the full HRC kit and I run leaded 110 halved with 91 pump (race gas, in my opinion, is the best thing I have ever done to my 300lb lover, or maybe my heated handgrips so I can ride in the snow!) Hope this gives you more to think about on the subject. :)

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I have had the unpleasant experience of an airfilter fire. It only happens to me when I'm performing the flooded bike procedure. The carb in theory cleans itself out and if you for one second let off that kill switch it fires through the carb...NOT GOOD...I've toasted two unis that way. I bought an Xr's only backfire screen which is way less restrictive than the OEM one.

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...Team Honda 'Batwing' for the airbox cures. You can purchase this from Precision Concepts or fabricate one (that's what I did)

Got any pics you can post or share via email of your Batwing :)

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