Hello, Just bought a new Zforce 800 and I'm looking to replace the stock air filter.What is the best replacement for it?What is the part number and where do I buy it?Hope someone out there can help.Thanks

Here is the Amazon link to what I ordered.  It works great for me.
https://www.amazon.com/gp/product/B001IZKIZ8/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[2015 Z Force 800 53/Trail EPS]

That's it and remember to order foam filter oil and cleaner as well.

THIS NOT DIRECTED AT ANYONE SPECIFIC, SO DON'T GET ALL OFFENDED.  I HAVE JUST SEEN A BUNCH OF IT LATELY.  EVERYWHERE.  MY WIFE ORDERS HER SHAMPOO ONLINE!?!?!   GO TO THE DAMN STORE.  HERE IS A NOVEL IDEA.  GO SUPPORT YOUR LOCAL DEALER AND BUY IT FROM THEM.  IF YOU DON'T HAVE ONE.  CALL ONE AND I'M SURE THEY SEND ONE TO YOU. YES IT WILL BE $8 MORE.  I KNOW. I KNOW. YOUR NOT MADE OF MONEY.  BUT YOU DO HAVE A $10K TOY.   PARTS UNLIMITED PART# 10112339        TWIN AIR PART# 156052FR. 

Ok, so I took a brief look at the stock air filter. 

So this is the bad one?  I'm familiar with the UNI's, use them quite a bit with good results.  The general consensus is to replace this one with a two stage UNI and put a dry foam filter at the inlet between the seats?

That looks like the new updated one.  I dont think you need to replace it but maybe someone else will chime in to confirm.

On the stock filter, the thickness of the foam sleeve was increased and the new "cap" on the end of the filter was switched to that black rubber/plastic

Twin air has the filter itself as well as the "dust cover" 156052DC

Be sure to use a good quality foam filter oil and proper cleaning procedures.

[2015 Z Force 800 53/Trail EPS]

Ok, so I took a brief look at the stock air filter. 

So this is the bad one?  I'm familiar with the UNI's, use them quite a bit with good results.  The general consensus is to replace this one with a two stage UNI and put a dry foam filter at the inlet between the seats?

Well, that is the revised CFM paper filter which "may" be better then the old ones that the end caps just fell off of but I still don't trust it so I advise getting the Uni or TwinAir asap. Now CFM also now makes a foam filter replacement for that paper one and it "may" be fine. For me and where I am, when it comes to air filtration, I go extreme...I know it..but it's because I have seen so many engine deaths because of particle intrusion..and so many last so long when there is none. The first and biggest thing is get a solid and trusted filter in the box and service it correctly and as often as necessary. Next is to get the intake out of that dust-packed area behind the engine and seat as the tires fill that area with crap constantly and..much of the engine heat is right there. Put another filter on it if you wish and if you do, you will thank yourself. I have tried several different filters up there and most have worked pretty well but I just ordered another Unifilter for it because...well..I want the best backed up by...the best.  Now I will have a 5x8" uni in the box and a 5x6" with a water resistant Outerwears prefilter on top. And I got to tell you, cleaning that top one is WAY easier then getting to the one in the box...lol

Good advice.  I don't ride in as much dust as you, but I understand why you're more careful.  I think I can lop off the top of that intake and find a UNI that'll fit on that plastic pipe.  I'd rather not take up any storage space in the cargo area, so plan to leave it where it is.  Thanks for all the replies.

[2015 Z Force 800 53/Trail EPS]

Yeah no real need for all that if you don't have the dust. Here we even have gypsum & talc dust that can either get through many filters or plug then up in a hurry. Anyone who had vacuumed up drywall dust knows all about that. When I'm tracking through a cloud of that stuff I don't want to be wondering if I'm ok, I want to know I am.   

This will work

Should it be a straight or angled UNI?

either or, some prefer the angles to fit the box, I have found no problem with either.
I keep the straight instock as it works with all bikes

[2015 Z Force 800 53/Trail EPS]

 Yeah both work but most use the angled.

I bought a CFM high performance air filter thats blue....oil foam but rigid and shaped a K&N. Part# 8703CF. I think thats a Canadian part#...should cross though.