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Discussion Starter · #1 ·
i just bought a 1996 regal 258 commodore with twin volvo 3.0 and wonder what it would take to convert to twin 3800s and could you use automotive 160hp motors? at least one motor is shot and maybe both
 

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Extremely expensive, the two biggest problems are:

1. The bellhousing on the 3800 is different than any other marine bellhousing out there now or ever and never used on a US marinized engine (with the possible exception of the Northstar V8 that was used in some ski boats). The one on my marine engine was made in either Australia or New Zealand, so these would be high dollar items and you need two.

2. The water cooled marine manifolds are also unique to this engine and, again made in either of the two places above.

I'd guess $3000 for two sets of marine manifolds and bellhousings and that's just for starters... If you want more power a 4.3L Chevy will fit the bellhousing you now have and is readily available used already fit for marine duty.
 

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I have the 4.3 in my four winns..starts EVERY time...sat all winter primed it twice and turned right over didnt run rough or anything. Edelbrock also makes a couple different cams for them :)
 

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3.0L Conversion

A couple considerations:
1) Engine width - The 3.0L is narrower than the V6, so twins can be mounted closer together. Maybe to close for V6's. Consider 30 inches between crankshaft centerlines as the minimum.
2) Drive Ratio - The 3.0L is usually mated to a 2.0:1 ratio drive (assuming single prop. I don't know of any 3.0L duo-prop applications). The 4.3L is used with a 1.65:1 or 1.81:1. Although you may get lucky and be able to find a set of props that will hold RPM's where they need to be, check the cost of regearing 2 drives, just in case.
3) Fuel consumption - The V6's will drain the tanks faster, so you will have reduced range and more frequent fuel stops with the current tanks.
4) The 3.0L's are cheap and plentiful. If the performance is adequate, save your money. MerCruiser sells a CPO (cert. pre-owned) 3.0 that lists for under $3300 U.S. Same base GM engine as the Volvos. You should be able to swap the bell hsg & coupler, adapt the exhaust, and go.
 
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