I am going to repower my 38 Commander this winter.   I am debating between two new 7.4L carbureted engines current I have 454s or go with 8.1L fuel injected.   There is a considerable difference  in price.   I am replacing the transmissions too.   Any advise or experience with either option regarding performance or other?   If I go with the 7.4L I am hoping my shafts and struts would not need modification.    If I go with 8.1L they need changing from what I was told.   8.1L is more fuel efficient, but has more HP so fuel savings might not be that much given the boat size.    

Thanks,

Mark

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Any idea of the lifetime of a stainless set of risers and manifolds in salt water?

Volvo Penta 8.1 stainless here:  http://www.stainlessmarine.com/shop/set-of-bb-manifolds-81-496-volv...

Jeremy Goldstein said:

Stainless marine and teage marine are two outfits that make all stainless manafolds 

Still have the original cast manifolds (exhaust) on repowered engines, always sweet water.

I also still have the original cast manifolds, on my original 327’s. Still work well after 53 years. Also always fresh water. 

The 454’s I bought will need new risers, they were salt water. I have no idea how old they are but I poked a screw driver through them. 

Timothy "Tim" Miller said:

Still have the original cast manifolds (exhaust) on repowered engines, always sweet water.

Here is my 2 cents

I have a 65 38 bridge with the 431's after much thought and research I am going with 383's here is why more hp and tq than 431, 427 and 454 carb. less weight, cheap parts and you can get help anywhere. I am going flat tappet counter rotating. 9:1 compression 460 ft lbs tq @ 3200. Cruise on these hulls is around 17-18 knots the most efficient speed based on GPH #'s hp at this speed is around 440 total 30+mph needs 600+ hp these numbers are with 2 engines. so well within the design range of a small block. 

Certainly no expert here,  but from the many threads on this subject, the biggest negative in repowering with small blocks,  is in order to achieve the H.P. and torque ratings you describe the engines need to be run at fairly high rpm. This may cut short the longevity of the engines.
 
Dave McKee said:

Here is my 2 cents

I have a 65 38 bridge with the 431's after much thought and research I am going with 383's here is why more hp and tq than 431, 427 and 454 carb. less weight, cheap parts and you can get help anywhere. I am going flat tappet counter rotating. 9:1 compression 460 ft lbs tq @ 3200. Cruise on these hulls is around 17-18 knots the most efficient speed based on GPH #'s hp at this speed is around 440 total 30+mph needs 600+ hp these numbers are with 2 engines. so well within the design range of a small block. 

I agree. I’m going the other way, when I eventually get to it I’ll be replacing my 327’s in my 31 with 454’s. My though is I’ll be running at a lower rpm not working the engines hard. The big block really aren’t that much heavier, about 200lbs. A buddy of mine has a 6.2 Mercruiser in his 26’ Maximum and he always wishes is was a big block, runs 3,800rpm to cruise at 25 mph. 

Drew Schneiderbauer said:

Certainly no expert here,  but from the many threads on this subject, the biggest negative in repowering with small blocks,  is in order to achieve the H.P. and torque ratings you describe the engines need to be run at fairly high rpm. This may cut short the longevity of the engines.
 
Dave McKee said:

Here is my 2 cents

I have a 65 38 bridge with the 431's after much thought and research I am going with 383's here is why more hp and tq than 431, 427 and 454 carb. less weight, cheap parts and you can get help anywhere. I am going flat tappet counter rotating. 9:1 compression 460 ft lbs tq @ 3200. Cruise on these hulls is around 17-18 knots the most efficient speed based on GPH #'s hp at this speed is around 440 total 30+mph needs 600+ hp these numbers are with 2 engines. so well within the design range of a small block. 

That might be a snug fit! Lol

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