Best flowing exhaust riser for horsepower?

I am going to build a 355 soon. I've read until im blue on this forum about making marine horsepower with small block chevorlets. I will build a 355 sbc with vortec heads, comp cams roller valvetrain and extreme marine cam,marine distributor and carb. The only problem i see with it all is the crappy exhaust manifolds/risers.

Of the 3 main cast iron types for wet exhaust small block chevy, which flow the best exhaust for making power(. Around 375hp) omc, penta or mercruiser

Re: Best flowing exhaust riser for horsepower?

I would probably read thru this thread http://forums.iboats.com/showthread.php?t=524489

however performance and cast iron manifolds are usually not in the same sentence.

Re: Best flowing exhaust riser for horsepower?

Of the 3 main cast iron types for wet exhaust small block chevy, which flow the best exhaust for making power(. Around 375hp) omc, penta or mercruiser

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Ayuh,.... None of 'em....

Re: Best flowing exhaust riser for horsepower?

I already new they suck. And I've ready that entire above thread twice now. Its a great thread, also loaded with a whole page of irrelevent information on what wd40 is and how to spray it on cast iron? Anyway i won't need 1-2k$ exhaust systems to reach my goal of 350 to 375 hp. Im not going to be turning 7000 rpm either. 5000 will be my limit. Ill just stick with the penta risers. I used them instead of the omc because the angle to my thru hull set up works better. I was hoping someone had tested these on a dyno.

Re: Best flowing exhaust riser for horsepower?

this is buried somewhere in that thread... not a dyno, but real world results.
In case you didn't already see it...

http://www.glmmarine.com/manifolds/images/ads/fpboating_0203.pdf

Re: Best flowing exhaust riser for horsepower?

Yes i must have overlooked that in the thread. I did see mention of them in the "building a 350 vortec" thread. Do you guys really think i cant get at least 350hp from these crappy risers i have? By crappy i mean air flow. I really hope i can. I dont see 350 to 375hp unrealistic. Do you? I mean yes i would love to buy 7000 dollars worth of stuff and build a forged 383 with super awesome exhaust and make 475hp but i cant afford all that right now. How do these merc powered new boats claim 350+ hp from a 5.7 running through cast iron exhaust mainfolds. Am i missing something? I know there are lots of variables at work. I know power is relative to hull design, drive, prop, weight etc. I also have a worn out 350 now maybe pushing 220hp so a jump to 350hp for 3000$ would really make me happy!! Thoughts please

Re: Best flowing exhaust riser for horsepower?

Tommywalton said:

Yes i must have overlooked that in the thread. I did see mention of them in the "building a 350 vortec" thread. Do you guys really think i cant get at least 350hp from these crappy risers i have? By crappy i mean air flow. I really hope i can. I dont see 350 to 375hp unrealistic. Do you? I mean yes i would love to buy 7000 dollars worth of stuff and build a forged 383 with super awesome exhaust and make 475hp but i cant afford all that right now. How do these merc powered new boats claim 350+ hp from a 5.7 running through cast iron exhaust mainfolds. Am i missing something? I know there are lots of variables at work. I know power is relative to hull design, drive, prop, weight etc. I also have a worn out 350 now maybe pushing 220hp so a jump to 350hp for 3000$ would really make me happy!! Thoughts please

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Not sure what kind of boat you have...
This member Mkos1980 has had great success with this budget combo with vortec heads. His boat is flying for what it is. Stock manifolds.

http://forums.iboats.com/showthread.php?t=290302

Re: Best flowing exhaust riser for horsepower?

new boats have cats and cast headers.

Re: Best flowing exhaust riser for horsepower?

Wow! See thats exactly what im talking about. The power is there right where i want to be through factory manifolds. I have a 1988 chaparral 2300 with cobra. With 2 people and a weak 350 i can get 47mph from it at 4300 rpm. Thats a 3 blade Michigan 19p stainless. I also have a 21p up front stored away ive never even tried. I bet with glassy lake alone with the 21p i could get 50. I think ill try it. Anyway thanks for the link this is almost identical to what i want to build and a little more than i expected to see someone get. I knew those manifolds would do it!