How many HP through stock exhaust manifolds?

[ROBIII]

Hey guys, how many HP can you run through a set of stock Mercruiser exhaust manifolds on a small block? I've got 350Mags and am about to start tweaking on them. I know heads or Imco's would be better but I can't afford them (gotta buy two sets!).
Also, do curved risers make a difference on stock manifolds or does the stock stuff suck so badly that risers won't matter?
ROBIII

[LeadFootTheRabbit]

RobIII, anything you can do to reduce friction is going to help. Curved risers, exhaust porting or headers all help the engine breathe better. The horsepower your motor can put out depends on alot of variables; compression, cam selection, ignition timing, carburation, fuel and on and on. Your exhaust system doesn't define the amount of horsepower your moter will produce, it only adds itself to the larger equation.
Good Luck! LDFTRBT

[CV-23]

Hi RobIII....The biggest problem with factory exhaust is weight(you could shed over 100lbs)....Factory manifolds and risers are alot better at flowing these days than in the past. New heads and cam and Hp over 400 would be a better reason to upgrade to performance exhaust. It is expensive...Mike.

[ROBIII]

Thanks for the replies. I guess what I'm really asking is can I drop in stroker kits and cams this coming winter and still expect to get good performance without upgrading the exhaust manifolds? The only thing that sucks about twins is buying two of everything!!!!!!!
ROBIII

[LeadFootTheRabbit]

RobIII, I think you might be putting the cart in front of the horse here. Cams and stroker kits are nice but what are you trying to achieve? Maybe if you spent your money on new exhaust systems, ignition timing and fuel jetting you might get what your looking for. You can always stroke them motors at a later time. Just my .02
LDFTRBT

[ROBIII]

Leadfoot...I, like all of you, want more top end. I'm spinning 23" Turbo's (counter-rotating) at about 4300 RPM WFO. I'd like the power to spin them closer to 5000 RPM at WFO. The reason why is that I'm stuck at about 59 MPH now with stock engines. Also, we're keeping the boat for several years. The majority of cruising is at 3500, that's why I was thinking strokers - more torque and HP but not spinning over 5000 RPM.
More top end without major expenses like blowers.
Does the new 377 Scorpion run stock exhaust or Imco style manifolds from the factory? If they can get 350HP turnkey, I sure as heck oughts be able to get 325 at least from mine!
If 270 HP each is good....Then 325-350 each ought to be great! I welcome your input. What do you think of the K&N flame arrestors vs. stock?
ROBIII