I'm considering moving up to one of the fountain 35s or 33 and am weighing the advantages of each engine package. Besides the hp difference, what costs and benefits do each offer. I've read that the 496s have cast internals and can not handle extended wot operation, but that the 525s require more regular maintenance. Also, how does the quality of the 496 compare to the old 502/454 MAG MPI. I'm a recreational boater but like to run hard on occasion and don't want premature failure. Would appreciate some real world advice. Thanks

In stock form the 496 is a great platform that will give you hundreds of hours of trouble free boating with basic maintance. Even extended WOT runs are really not a concern.

The 525 is a great motor and puts out alot more power. It will cost more .....alot more and will need valve adjustment and head work around 350 hours. The older 525s had some header leaking issues. The 496s run great as a stock platform and will be cheaper to buy, operate, and insure. How fast do you want to spend is the question as always

While I don't have either I am in the same position as you and have given this much thought.The 496 is a great motor and while some will disagree it seems that if left stock are very reliable.The 525 is a better motor but are very prone to header leaks.In my opinion the only way to fix is to re drill the heads and use manifolds unless you want to test your headers every 20 hours and replace every few years.
I still don't know what I want but I wish there was a bolt on manifold for the 525.

I can't speak 4 the 496's other than I know people w/ them & have not heard them say much of issues w/ them! I can speak 4 my trip 525's & how flawless they have been! good luck!

I had both motors in the same type of hull.
2002 Avanti with 496 Ho mags and now the 2008 Avanti with 525's.
First, the 496's had header problems as well. The CMI headers or the Merc headers are almost identical and similar issues. You hear more about the 525's since most of the 496 headers were STD Merc, and not CMI headers. Only some had the CMI headers. (ALL CMI headers had and have issues, but thats a different topic.)
For the $ the 496 are great and reliable. If you need more HP and more speed 525 is the best choice, with out going to blowers. On the same hull the 525's gave me about 12-15 MPH, but the additional cost you have to justify for your self.
525's need more maintainence but you can run them harder and higher RPM's
(Not sure of the tech data, but I think the 525 rev lim is set at 5400 and the 496 is to 5150+-) So more time on higher RPM's more TLC required.
Knowing what I know now, dealing with Merc. Racing and CMI with different issues... well...uhm.. to not satisfactory results, I would build a reliable standard carbed 502 with 600+ HP's and just forget about all the electronics and computer stuff that Merc. offers, for half the price. I got the Merc 525's when I built the 08 Avanti for the national warranty and the smart craft system, electronics, blue color, etc. At the end of the day it's not worth it. Few shops really know what they are doing anyway so having a "non Merc." motor out ways the cost for the name.
All that being said, I am very happy with the 525's and I had it dinod at 580HP and 581. If you have a near by Marine facility with a good rep on 496's AND 525's fine. If not.. go with a standard 502 carb with more HP, less $.
My .02

PS; neither my 496's or the 525's had any major issues. (aside from the headers, and I have that pretty much figured out.. )

It's nice to hear the 496s hold up. I love the look and sound of the blue motors but am afraid of the total cost over its life compared to the 496s. I average 100 hrs/year in the Great Lakes area and want turn key reliability and ease of having them serviced when problems occur. There are some good deals out there on Fountains with both packages, and I really appreciate your input.

The 496 motor definitely hold up. I have a friend of mine who has put 850 hours on his and it has yet to give him one problem in 8+ years of use. They are extremely reliable if left stock.

525's
Great Motor trouble free 210 Hrs.
Can't speak for the 496's.

525: Dropped a valve at 172 hours resulting in a complete rebuild. Now it's 509 cubic inches...... Mechanic hear some chatter and I should have done something about it but live and learn.....