Increasing the performance of a 351 H/M

[sandslot]

I have a 1971 Classic 18 with 351 H/M motor in it. Don't know if it matters, but years ago the rotating assembly/block was replaced due to a cracked block. It runs well, but I want it to run stronger.

What can I do to strengthen it? It has a few small oil leaks and I suspect hundreds of hours, so I plan to take it down. Suggestions on content? Any improvements needed to the 270 stern drive suggested? Currently runs low 50s and would like to pickup 10mph-ish....

Thanks!

[gcarter]

A new SBF w/a little over 400 inches would help.
I don't speak SBF, but there are folks here that
speak it very well. The H/M moniker meant very
little, just a supplier as far as boat engines were
concerned.

[mattyboy]

Getting another 10 mph out of a Volvo 270 boat is a bit harder than a Chevy merc boat. It can be done but will be more money than a similar Chevy setup as GC said the HM just marinized what the auto world had at the time. The first 351 w in 69-70 were 290 hp motors after that the HP rating fell to 260 255 233 as the 70s went on

As an example a stock merc alpha with 260 hp will be closer to high 50s close to 60 in stock form.

The ford Volvo is a strong setup and refurbed it will power the boat for another 40 years without issue just not at 60 mph

[Pat McPherson]

My 1975 18C would run about 60mph with 325HP 350 Chevy and Volvo 280.

I don't know what the differences are between the Volvo 270 and 280 are. I do believe that you can build a 325-350HP Ford 351 without much trouble though.

As Matt said, a Merc Alpha drive is much more efficient; my 1987 20' Minx would run above 60mph with a 270HP 350 Chevy.

[JimG]

I can see 54 with my HM 351, Volvo 250 and Ultra prop. That is about as fast as I want to go in the old girl!! Mostly cruise in the mid-40's.

[sandslot]

I can see 54 with my HM 351, Volvo 250 and Ultra prop. That is about as fast as I want to go in the old girl!! Mostly cruise in the mid-40's.

I have a 1971 351 with a V270......what prop do you think would maximize speed? I am not real concerned with launch and wont pull skiers with it....thinking a 14x23....agree?

[mattyboy]

All one needs to do is read Bill s thread on his 16 he built a killer sbc over 400 horse an had a Volvo aq 290 the last revision of the old Volvo and he was trapped in the mid 60 s. Granted the hull on an 18 is a mph or 2 faster than a 16 350 hp in a Chevy is easy In a ford your looking at 2500 bucks or more in exhaust alone

[mattyboy]

Assuming your 270 is 1.6
Solas Titan 19 pitch 220-300 HP
Solas Titan 21 pitch 300-350 HP
Solas Titan 23 pitch 350 + HP

Your goal would be to turn a 23 Solas to 5000 rpm on a 1.6 drive that will handle ok and will be mid low 60s but you are looking at Motor with a lot of Ballz

[JimG]

My Ultra transformed my boat from an ill-handling beast to a real sweetheart. I don't know if it is the ultimate for top speed. I do not run that hard any more, lol! Lots of good info about the Solas props on this site, might be faster. Matty would know. I can pull a 14x23 (re-pitched 24) Ultra to about 5200 and 54mph... stock 351, Weiand manifold and Edelbrock carb.

[sandslot]

My Ultra transformed my boat from an ill-handling beast to a real sweetheart. I don't know if it is the ultimate for top speed. I do not run that hard any more, lol! Lots of good info about the Solas props on this site, might be faster. Matty would know. I can pull a 14x23 (re-pitched 24) Ultra to about 5200 and 54mph... stock 351, Weiand manifold and Edelbrock carb.

The engine does have a Edelbrock intake & carb as well as high-flow exhaust already.....does about 50, so even with the 14x23, I'll never see 60, without going into the block (bore/cam, etc).....sounds like a SBC and Mercruiser is the way to go. Is that what I am sensing??

[mattyboy]

Yes if speed is what motivates you yes Chevy merc or if keeping alive a piece of history for future generations and speed is not an issue go ford Volvo. But be warned on a vintage boat this may be a slippery slope you may find rot and water in stringers transom not to mention the tank.

[sandslot]

Yes if speed is what motivates you yes Chevy merc or if keeping alive a piece of history for future generations and speed is not an issue go ford Volvo. But be warned on a vintage boat this may be a slippery slope you may find rot and water in stringers transom not to mention the tank.

Honestly, my preference is to keep the original equipment, but I would like to achieve 60mphish...what would you recommend to get there (with the 351)? Also, I have to rebuild the 270 - I assume parts are available??

[mattyboy]

honestly at this point the boat is a candidate for at least a full mechanical resto with some glass work for the stringers to beef them up for the increased speed. Not to mention the fuel system parts for the Volvo can be found but some parts are not around anymore same for the HM stuff so that needs to be taken into account
What's your budget?

[sandslot]

honestly at this point the boat is a candidate for at least a full mechanical resto with some glass work for the stringers to beef them up for the increased speed. Not to mention the fuel system parts for the Volvo can be found but some parts are not around anymore same for the HM stuff so that needs to be taken into account
What's your budget?

I have a budget of $7K (plus a small slush fund) for the entire refresh (hull, gelcoat (Ill do the work), powertrain)

[mattyboy]

The rule of thumb is for every mph you want to go faster budget 1 K so I would get a figure for your hull work and see what you have left for powertrain