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ORIGINAL VS MODERN POWERPLANT

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rbay:
Looking for any and all input.

I recently purchased a 1973 CV21 to restore.  It has a newer Berkeley jet pump, but no engine.  The first two paths engine replacement could take are both in the same 300-350 hp range:
1.)  Replace it with an early 70's vintage Olds 455 big block like original.  Would at least start with a marine engine, possibly a non-runner for complete rebuild, or something more together.  I'm pretty certain I would use a Holly Sniper EFI fuel system and an HEI distributor, but otherwise pretty old school.  Would integrate into the electrical system, gauges, etc. like the original.
2.)  Replace it with a 2000's Mercruiser 6.2L engine.  Might be something needing repair, or drop in ready. Would have modern ignition, fuel injection, but no doubt present some challenges integrating it into the original dash and controls.  Might be a few $1000 more than the Olds, but worth it to have the later technology?

So when thinking about reliability, driveability, sensory, fun, resale, servicing, what would be your vote?  I know fuel economy will favor the newer engine, but Michigan summers are pretty short and I don't get to put that many hours on my boats, so that takes a backseat to the other factors.  Or am I missing some things to consider?

A third possibility would be a modern big block, like a 2000's Mercruiser or Volvo Penta 8.1L, which would be 375-400 horsepower and another few $1000 more....but would that be worth it?  Would the extra HP really result in a better boat?

Thanks for you thoughts.....option 1, 2, or 3?

Plugcheck:
Why limit to three options?   What is the overall condition of the rest of the boat?   Just about anything can be configured to connect to that drive.    What is the long term thinking?   Period correct restoration?   Go fast have fun?   Honestly you could find a reasonable small block to drop in to make it operational for the 23 season, take what was learned and go forward in the fall.  Just some ideas

rbay:
Hi Plugcheck,

To answer your questions:
1.) You're right, there are a lot of options.  I thought the three I chose:  original big block, modern small block (same HP), modern big block (more HP) covered a lot of the variants and would bring out the majority of the pro and con arguments.  On a personal level, I was a 30-yr GM engineer, so I have more experience with GM engines.
2.) As far as current condition, the original upholstery is in good condition, and I'm hoping the hazing on the gel coat will wet sand off.  Some missing pieces, the windshield frame and grab handle in particular, will be a problem.  But I'd still like to get as close to original as possible.  That said, there is no shortage of older hot rods and muscle cars being restored with modern motors.....this could be the boat version.
3.) Speed isn't my #1 priority.  This is about cruising around the local 800-acre lake with wife and dog, and having a high probability of getting back to the ramp without a tow.  Well, maybe a place diverter rooster tail would be cool.....

carlsoncvx18:
If you do not care about originality. 

I would lean towards the gm6.2 they make a lot of hp and torque their light weight.   

Plugcheck:
A mouse or ls would certainly be a cheaper build than a rat, although not as high on the cool factor.    The 6.2 is a fine powerplant, but the 5.3 shouldn't be counted out, powerfull and plentiful.    A place diverter is very high on the cool factor scale, but Im afraid Id get in trouble with one if I had it. Likely you are more responsible?.

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