Conical filters are a mixed bag. I had one on a Corrado once. They are louder at full throttle, and kinda cool sounding, and if there's plenty of airflow, they work pretty well and probably add a couple of hp. However, in hot weather, there's usually more powerloss than normal. It's usually a 50/50 benefit thing I believe. I wouldn't buy one myself, but the one on my Corrado that I owned sounded so cool, I decided to keep it.
I had an open-element filter on my 850 T5.
I took it off and bought the in-box K&N.
Seriously, there was no real increase in power using the open element filter and as George has stated, the heat is an issue. In-fact, the heat made the car run very bad at idle. The temperatures under the hood while in traffic during the summer were very bad for the car to suck in. Once the car was moving and the air-flow was enough to cool the air within the engine compartment, the car ran okay. After playing around with this for a week I went to get my K&N drop-in filter. The performance was better IMHO with the drop-in. The power at high RMP was there and there was no hot-air issues upon take-off to deal with. The best part about all of this is the fact you don't have to worry about rain and water. Open air filters offer little protection against ingestion of water in wet weather. (Something else to think about.)
In short, get the K&N in the box. Don't chance-it using the open element filter on the 850.
In nice cool weather, it work like a charm. If it's 90 some degree out, it would feel a lot worse than driving the same car but with stock air box.
No heat shield will do the job that well, at least for the existing limited space and setup. Even when I relocate the battery to the trunk and put the cone all the way to the front and bottom of the car (away from the heat source), it will still suck up enough heat in any hot day to make a slightly modified 540 somewhat competetive when running against my car. Oh wait....it was before I reached 3rd gear.
All in all, if you don't mind the trouble and have lots juice left even in hot days, do it. If that's going to be one of your few modifications...try not to waste your time.
Well-said, Kai! Thanks for backing me up. Yeah, the open element filter on an 850 in Florida...not a good idea. Even if you drop the filter with a "cold-air" pipe to the bottom of the car, it will be sucking heat and crap from the asphalt. In Fla, the humidity, sand, and critters are pretty bad. Keeping the air intake at the front of the 850 is the best idea. Your setup is great, but you are running 400 CHP by now. (Damn, I miss those quick road-trips we took before I left.) Anyhow...just wanted to help shed more light on the 850 bunch before getting some work done.