2004 Mercruiser 3.2 L power loss

[VenisonLuver]

2004 Mercruiser 3.2L Alpha One. Normal operation tach 4500 RPMs and over 50 MPH. I recently replaced the manifolds. It had dry joint risers. The original riser gaskets had one side full open and the other restricted with a small hole. My replacement came with 4 full open and 4 closed ring gaskets not integrated with exhaust gasket. I drilled holes in 2 of the closed gaskets to match the original configuration. Now the engine runs smoothly but at top end I can only get 4100 RPMs and about 42 MPH. I've lost about 20% power. Is there any link in the loss of power and the manifold flow?

 

[achris]

That sounds like aftermarket (Merc gaskets are fully integrated). And aftermarket could also explain the loss of performance.

 

[VenisonLuver]

The manifolds seemed identical in every way. It sounds like you are confirming that the manifold flow can inhibit power. Would a full open configuration improve my problem? Thank you for your quick response.

 

[Scott Danforth]

do you mean 6.2? or 3.0, 4.3, 5.0, or 5.7?

 

[achris]

The manifolds seemed identical in every way.

Externally maybe. But it doesn't take much to change flow internally.

It sounds like you are confirming that the manifold flow can inhibit power.

Yes it can. Just ask anyone who's changed out the factory cast iron exhaust manifold on a car engine for a properly designed and built set of extractors.

Would a full open configuration improve my problem? Thank you for your quick response.

By 'open' I assume you mean through hull, and not thru-prop. With the current manifolds no, the flow restriction is in the manifold, not down stream. But even with Merc manifolds, thru-hull changes little (it's just obnoxiously noisier).

Chris......

 

[VenisonLuver]

Oh sorry, by full open I meant changing the restricted disc gasket for the open unrestricted gasket. Would that improve my power loss. The through hull part threw me.
Thanks again

 

[VenisonLuver]

Externally maybe. But it doesn't take much to change flow internally.

Yes it can. Just ask anyone who's changed out the factory cast iron exhaust manifold on a car engine for a properly designed and built set of extractors.

By 'open' I assume you mean through hull, and not thru-prop. With the current manifolds no, the flow restriction is in the manifold, not down stream. But even with Merc manifolds, thru-hull changes little (it's just obnoxiously noisier).

Chris......

Oh sorry, by full open I meant changing the restricted disc gasket for the open unrestricted gasket. Would that improve my power loss. The through hull part threw me.
Thanks again Chris!

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