Raylar

Bringing this post back to the original question and information requested by the Ajfisher.

In my opinion based on the overwhelming fact of issues with the HP525efi headers and leaks I would not recommend by a used set of these Merc Spec. headers and putting them on any good BBC marine engine. In my opinion the risks of leakage and serious engine damage are to great.

My suggestion is to spend a little more money and time and buy a really good set of 496 kit type (true) headers and you might see 2 or so mph if everything else of the boat is dialed in properly.

We all know on many boats there is a bit of speed locked up in props and such that can be unleashed with some expert applications. You've got to look at it from a "best bang for the buck" approach unless you've got an unlimited budget attached.

Best Regards,
Ray @ Raylar

AJ POWERPLAY

iTrader: (1)

Thanks ray... I see Dana marine has what looks to be a good value @ 2300$ (compared to others) and have shown in independent tests to actually put out more power than lightning headers... Prop work and hopefully a tune will go along with it, so hopefully 2-4 mph will be in reach

Michael1

I don't see how putting headers on a 496 with a speed density fuel injection system is going to get you any more horsepower, unless it was tuned by the factory too rich for maximum power. If it was, they probably had their reasons (detonation perhaps?).

Michael

thirdchildhood

iTrader: (6)

Just experiment with the props. Hold off on the exhaust until you are ready to do more. Your factory exhaust flows fine and if it's the aluminum version it's actually very desirable. People were scrambling over each other to buy my old set. There is no quick way to get more power from the 496. You could go with a Raylar kit or bolt on a pro-charger til she comes apart but I've already said what I would do.... go to a 502 based engine

Ray, nice to see a smiley face instead of the usual winky .

POWERPLAY J

Go through the right guy and you could do carbed 540's. Wtf is it with them that turns people off? No bullchit bells and whistles, trouble shooting is a breeze and they will last just as long or longer. I would not plan on messing with the 496's if you wanna go fast on a budget look elsewhere.

Raylar

As for power and speed gains with good header upgrades on Merc 496's, there have been probably thousands, some have seen 2-3 miles per hour, some have seen 1-2 mph and some have seen zip miles per hour. This will always be a factor of how well a particular model boat and hull responds to small extra power of about 7-10% and how well the boat is set up from a standpoint of ideal propping, hull conditions, X-dimensions, air temps, water type, speed measuring accuracy,etc., etc.. No two boats of different manufacture, size and set up are going to respond the same-period!
I know here on OSO its constant conversation to make these comparisons but most of the time they are rarely valid.
There is a good possibility that with a real good set of headers and after header exhaust system a stock 496HO for example can see 30-45HP and some good addtional torque. That addtional power and torque if EFFICIENTLY AND PROPERLY applied can usually equate to some small speed increases and if the systems on the engine are changed to add real power from addtional breathing then the power from the headers becomes more significant and the need for the headers becomes more important.

If marine engine header systems were not neccessary or important for power production, why would every major marine performance engine manufacturer of engines 500HP or more equip their engines with these more expensive systems if good old straight manifold systems were totally sufficient? Are many aftermarket manifold (called headers) systems capable of providing any significant power on a stock 496MAG or HO engine in my opinion, testing and expierence -NO. The Mercury exhaust on the stock 496 is the best manifold type exhaust ever OEM equipped on a Mercruiser engine. Also different types of headers ,ie short tube E-top type headers on stock Merc 496's will and do produce less power than longer tube sweeper type headers, plain and simple.

I think in my opinion again, every boat owner who has a boat that was ORIGINALLY EQUIPPED with a late style efi engine should refrain from changing out this type of original engine type to an early carburated engine, why? Because if they ever plan to sell the boat and move into something else, the BUC valuation on their boat has pretty much been destroyed because it does not have an engine type the boat could have been ordered with or sold. This makes a new buyers chance for lending if needed almost impossible although I hear lending is tough today anyway. why make it worse. Most savey buyers are going to want an engine that the boat came or could come with thats dated(age) with the boat.
If one plans to keep the boat until it disolves or such then not a worry and you could equip it with any nice reliable marine engine and boat till it disolves. Just something to think about before a performance boater goes tossing an old technology engine no longer offered by major marine engine manufacturers if a boat is equipped otherwise.

Again, I as well as others with more knowledge and experience than me cannot stress enough the importance of getting the correct prop type and spec. on a boat that is looking for the best speeds and overall performance and the condition of the hull and drive height have a big influence on how the boat will ultimately perform.
Again it's a whole boat, whole system approach that always nets the best results.

Best Regards,
Ray @ Raylar