[herm5000]

I have 2000 z302 that came stock with a 7.4 mpi and silent choice exhaust system. The original engine is toast. My research indicates that the z302 came wth the mercruiser 525sc as an option in some years. There were other high performance engines offered also. Boating magazine actually talks about this in a 1999 article. I have secured a fresh 525sc as a replacement engine but gave some questions about the exhaust system. This engine did not have the exhaust manifolds and so I need to replace them. The original manifolds were Gil marine. I have talked to a few manufacturers and am being told that I need to know if the hull exhaust locations are standard bravo location to know what risers I need. From what I am reading the z302 hull exhaust locations are wider and maybe higher than standard(is this true?). Therefore standard riser tubes won't work. Am also being told that the 525 needs the high performance risers that mix water at the end of riser to prevent reversion the stock 7.4 manifolds and risers are out for this engine. But the high performance risers are too long to use the silent choice system. So my questions are :

What type manifolds , risers/tailpipes did mariah use on these high performance installations? Did they install these hp engines with silent choice systems and if so what kind of riser tube was used to prevent reversion?

My present system with the silent choice angles in to meet the risers sense the factory holes are wider than standard bravo ( I think). If you bypass the silent choice and go strait to thru hull exhaust tips is there an angled pipe that was used to go between end of riser and exhaust tips. How did they accomplish this? Don't know if flex pipe will bend that much.

I would really appreciate all input on how I could make this install work and still protect against reversion. Thanks so much

[Motoxxx43]

Welcome to MOC!
I have the 7.4 in my 250. I tried to put some performance manifolds/risers on it from a 454mag/502mag. Two things happened. One- the ports are not the same. 7.4 has peanut ports the performance motors have large rectangle ports. Your 7.4s would not have worked even if they fit.
Two- the performance manifolds did not line up with stock exhaust even thought they bolted right on. The options would have been to straight tube it and cut out through prop and captains call or do something fancy and most likely expensive. Needless to say my 7.4 is stock form.

The 525 is a blue motor. There are Mariahs with the 500EFI which is also a blue motor. Outside dimensions should be the same aside from the s/c part. >>HERE<< are some photos of a 500EFI in a z300 to give you an idea of what the exhaust looks like in a Mariah. I have no idea if that is a custom routing specific to Mariah or not. Im going to guess it is not, but what do I know!? Id research exhaust from manifold/risers to hull topics on forms that deal in high performance boats like Offshoreonly, powerboatsonly, ect. Maybe even some phone calls to performance shops like teague marine or arizona speed marine.

Just putting this out there- per the brochure the 300/302 are rated to 490hp.

[herm5000]

Thanks for the reply. I have come to the conclusion that I will have to do away with the captains call and exhaust through the outdrive to make it work. Just wondered if there was a stock pipe that was made to go from end of riser over to thru hull exhaust tips since they don't come straight out behind the riser. I guess flexible wet exhaust pipe is an option.

[Motoxxx43]

That flexible pipe is what I was referring to. In your case it would be a wise idea to call a performance shop an ask them about the manifold/raisers... The blue motors are not in the same ball park as the black mercruisers. What I'm trying to get at is they prob won't work with those big cast manifolds. They were designed to be ran with a performance exhaust.