John, I have a k&n on my '81. While I can't tell any difference or gain in hp, like they claim, I still feel it's worth the money. I do think it breaths better, allows more airflow. Also, unlike regular air filters, you don't have to buy a new one all the time, you just clean your k&n every 50,000 miles, give or take, depending on how dusty and dirty the air where you live is. They only take an hour or so to clean, so you buy one, spend an hour every 50,000 instead of buying a new filter and save $$$. hope this helps you out,
John, I have a K&N in my 81 for 3 years now and I can't really say that it increases HP but it does improve air intake which should increase HP. I did notice better throttle response. I think they are worth the investment. After all it is the last filter you will need to buy for your Vette.
I just installed my K&N Filter/Kit this past weekend in my 85'. We went for short cruise (100mi) It sure responed better and seems to have better pick-up at the low end. I'm gonna keep it!
In a recent magazine article I read, dyno tests showed a gain of 3-5hp using K&N and similar type filters. But in some cases it actually reduced power. This was due to the filter having to much oil on it and reducing the airflow into the carb. I use one in my scoop but I can`t say I noticed any improvement over the original paper filter. The main benifit is that they can be reused but be sure to use the reccomended oil when you clean it.
Whether or not a K&N filter is going to be responsible for a noticeable increase in performance depends on the size of the filter and the air flow through it. For example, 90-96 C4s use a huge panel filter. Up to about 500hp, a K&N is no advantage over a clean, stock filter.
You look at other GM V8 applications, such as pre-82 Corvettes, older Camaros and Firebirds or some truck engines and you see the stock filters used there are small and K&Ns can be a significant advantage. This is especially true of engines modified for increased performance but still use a stock-sized air filter assembly.
One thing many don't understand about the comparison of paper filters to the K&N (oil-impregnated, cotton-gauze in a wire framework) is the paper filter's air flow capacity is less tolerant of contaminates. This means, as the paper filter traps dirt, it becomes restrictive at a faster rate. This effect is so pronounced that it doesn't take much contamination before a paper filter will have a noticeable restriction, compared to a K&N with the same amount of dirt trapped. Because of this, in a case where a K&N replaces a paper filter having adequate air flow when it's new, the engine may see improved performance during the period of time that paper filter would have been in the second half of its service life.
Lastly, the biggest advantage of a K&N is it can be reused. Once it gets dirty, you just wash it, dry it, reoil it and put it back in. If you are a finatic about clean air filters, you can do that once a month if you want but you'll never spend a dime for a new filter again.
I've used K&N filters for over a decade and have, no doubt, saved a lot of money because of it.