Thank you for the member approval for slantsix.org. I'm in the process of restoring 1971 Chrysler Sport Crown tri-hull. I have two sizes available for rebuilds: Volvo Penta B30 AQ170A/270 inline 6 and Chrysler Marine 155 slant six (I don't have serial number currently available).
What's my best option between the two engines? Any information, suggestions, and recommendations are greatly appreciated. Thank you. Johnnie

Well, both are inline engines....

What did the boat come with?

The Slant is certainly way cooler, and of course was made by Mopar...I believe the Volvo was made by...well, no one even knows who made it.

I thought that Volvo Penta only built the out drive portion. With just about any brand of engine in front of it

I know for sure that my neighbors when I was a kid had a tri hull with a Volvo Penta outdrive and that boat had a straight 6 Chevy 250 cid in front of the Volvo.

A million years ago I had a Bayliner boat with a Volvo engine and Penta drive. It squeaked like a little mouse all the time but it ran OK.

We had two Sport Crowns, but only restoring one, Originally the Aq170A engine. Slant 6 by mopar be easier finding parts?

Uh, false. The Volvo engine was made by Volvo. It is a marinised B30, which is a very stout and dependable 183-cubic-inch (3-litre) engine.

Aside from bigger displacement in the Chrysler motor, there is no advantage either way. They're both excellent engines in stock form and can both be readily upgraded to whatever degree you wish. They're also both long obsolete, which means some parts are challenging to find.

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Too many people who were born on third base actually believe they've hit a triple.

Yes, Volvo made it....but no one knows who that is!

Welcome! Parts for the slant six are much more available than the penta and the penta parts can be ten times the price of slant six parts.

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These ones go to eleven...

Oh, now. Volvo B30 rebuild parts are not difficult or costly to buy.

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Too many people who were born on third base actually believe they've hit a triple.

I know nothing about boats.

And I know less about Volvo inline six cylinder engines.

I would build which ever one would be most suited for what you want out of the boat. Fuel efficiency, top speed, historical correctness, Wow factor, or cost to rebuild...? In the end, unless the boat is going into a museum, decide what you want from that point and see if you can work backwards...

The SL6 is has a much longer stroke then a Volvo B30 so the Slant is going to produce more torque lower RPMs.
Both engines are rated around 145 HP but the 225 SL6 gives you 215 ft lbs.at 2800 where the B30 is 160 ft.lbs at 3000 RPM.
Under-square vs an over-square engine preference, for sure.

Keep this in mind if you change from one engine to the other because prop "pitch" and other operating system "details" could put you outside of the best HP/ torque RPM for the alternate engine.
In my mind, low RPM torque "wins-out", especially in a recreational boat application.
Just opinion on my part because I have never owned a boat.
DD

Lets talk boats and sparks. Gasoline fumes fall, not rise. The U.S. Coast Guard specifies that Starters, Alternators, and Distributors for boats cannot produce sparks open to the bilge. Therefore those items cannot be of the automotive type. Don't buy them from Autozone (or other auto parts stores). They must have a USCG Approved sticker on them.

Carburetors must also be USCG approved. If the float sticks (or becomes a sinker) the overflow tube must dump the fuel down the carb throat, not into the bilge.

This is why inboard and sterndrive boats have a bilge blower. Run it 5 minutes before you start the engine to evacuate those gasoline fumes.

Anchors away...... or aweigh?

I'm not saying you, or the Coast Guard, is wrong...but let's be honest. .00001% of all boaters run the bilge blower for 5 minutes prior to start.

In my career as a marine mechanic, spending numerous hours around water and boats, I only ever saw one boat explode into flames and burn to the water and sink. But.... it happens. Hence the precautions of fuel and electrical equipment being specific to marine applications.

Here is a link to my favorite example of gasoline fumes..... It is quite impressive. Enjoy!!!

https://www.youtube.com/watch?v=3f4lPzxSm5A