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sandslot
08-15-2016, 12:08 PM
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
08-15-2016, 05:13 PM
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
08-15-2016, 08:32 PM
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
08-16-2016, 01:07 PM
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
08-16-2016, 01:11 PM
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
08-16-2016, 01:18 PM
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
08-16-2016, 01:55 PM
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
08-16-2016, 02:37 PM
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
08-16-2016, 03:12 PM
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
08-16-2016, 03:24 PM
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
08-16-2016, 03:42 PM
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
08-16-2016, 03:55 PM
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
08-16-2016, 04:06 PM
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
08-16-2016, 04:45 PM
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
08-16-2016, 04:52 PM
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

tmdog
08-17-2016, 06:31 AM
The general rule is 15-17 hp equals 1mph increase. Dragging a Volvo od that equation may be out the window.

mattyboy
08-17-2016, 11:02 AM
on a 7k budget you will get more bang for the buck in the chevy world than you will in the ford world and the chevy will bolt up to the 270

the chevy and volvo combo is pretty tough too

Pat McPherson
08-17-2016, 12:29 PM
on a 7k budget you will get more bang for the buck in the chevy world than you will in the ford world and the chevy will bolt up to the 270

the chevy and volvo combo is pretty tough too

Matt has a good point. Lots of options for SBC and marine accessories are much more accessible.

You could pull your original 351 H/M and accessories and store for if you or someone else ever wanted to return the boat to it's original configuration.

I sold my 1975 18C in favor of a 1987 20 Minx because of the Merc drive had trim and was much more available. I do like the 18 Classic boat better and plan to go back to one at some point down the line.

sandslot
08-17-2016, 12:32 PM
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

Sounds reasonable...Is there specific hull work that's recommended? I'll have the deck off next week. I could do a two-stage project - first part as you recommend and the second part the powertrain.

Do you think I can get parts to rebuild my 270 Volvo?

Pat McPherson
08-17-2016, 01:45 PM
Sounds reasonable...Is there specific hull work that's recommended? I'll have the deck off next week. I could do a two-stage project - first part as you recommend and the second part the powertrain.

Do you think I can get parts to rebuild my 270 Volvo?

I'd plan to replace the fuel tank if you are pulling the deck.
Check the stringers and transom for cracks and or rot. Unfortunately a 45+ year old boat is bound to need some work...

turbo2256
08-17-2016, 06:00 PM
Bigest hold back on a 351 ford are the cylinder heads they were designed for a 289 even though the older 351s had slightly larger valves and ports. Best to go with aftermarket heads as a start. First thought is do you want cast iron or aluminum? Fresh water or inclosed cooling system aluminum ok for fresh water. Cast iron for salt or aluminum with a coating thats about a 1000.00 option or inclosed cooling. Heads are about all there is holding back a ford compaired to a SBC.

mattyboy
08-17-2016, 06:24 PM
A mechanical resto would be all fuel lines and tank as well as new wiring then powertrain

gcarter
08-17-2016, 07:17 PM
Take a look at this thread about some restoration work I did on an old 18 Barrel Back;

http://www.donzi.net/forums/showthread.php?49388-vonkamp-s-Barrel-Back-18

If you have any questions, don't hesitate to ask.

Craig S
08-28-2016, 05:10 AM
Im in the completion phase of two 418cid 351w. Ill keep you posted. Forged pistons, cast Scat crank, H beam rods forged. Roughly $1500 balanced with Harmonic Balancer...each plus machine work.

427 Windsors were much more (2k+) due to only being available with forged crank. This was little different in price from rebuilding my reciprocating stuff with new pistons.

I think we're at 10 to 1 compression. Ported and big valve 1969 4bbl heads. Offenhauser 360s, Holley 750s. Comp Cams.

Craig S
08-28-2016, 06:09 AM
Fwiw...just noticed your budget. Mine is 10k for the two engines. Long blocks built by machine shop. New cam and kits (one custom ccw). 700 worth of Mallorys. A new 750 Holley. 3 blocks pyrchased in addition to 2 i had. The plight of dealing with a bunch of non running parts and no backstory.

Machining and modify standard 69/70 4bbl head to match other big Chebby valves and matched porting of other 3 heads (as i had 1 cracked head). Same with 1 Offenhouser 360 intake.

I was told NOT to buy the $700 per set aluminum 351w Chinese complete heads off ebay. They would have saved a ton, but the machine shop has seen seats fail in 50 miles.

HallJ
08-28-2016, 11:50 AM
If you want more speed, raise the drive up 2".

Jeff

turbo2256
08-29-2016, 05:00 PM
Im in the completion phase of two 418cid 351w. Ill keep you posted. Forged pistons, cast Scat crank, H beam rods forged. Roughly $1500 balanced with Harmonic Balancer...each plus machine work.

427 Windsors were much more (2k+) due to only being available with forged crank. This was little different in price from rebuilding my reciprocating stuff with new pistons.

I think we're at 10 to 1 compression. Ported and big valve 1969 4bbl heads. Offenhauser 360s, Holley 750s. Comp Cams.

Dont know your heads air flow but well done there small for that many cubes. Also you will have a realy ruff time finding spark plugs in the proper heat range as most popular plug for a sbf with 18mm plugs have been discontinued. Either too hot or too cold is all thats left. Have been dealing with this for years on my 460 and 302.

sandslot
09-13-2016, 12:15 PM
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?

We discussed powertrain improvements needed to go 60+....what about structural? I'm thinking I'll add a few stringer braces throughout the entire hull. Seems to be a few short. I already have a large gray-colored "triangular" one in the bow (about 2' from tip - can be seen below)), but seems more are needed. It also seems to me more structure is needed to strengthen the cockpit-hull interface too. Suggestions/thoughts?
85032

mattyboy
09-17-2016, 11:40 AM
usually once the main stringers are confirmed as solid and dry or replaced beefing it up is done with gussets that run port to starboard and some also use coring to make the hull solid higher speeds mean more torque and pounding stresses on the structure make sure you have weep holes and seal everything

gcarter
09-17-2016, 01:42 PM
IMHO, tying the gussets into the hull sides will generally result in the bond in the hull sides will eventually break loose,
because the bottom and the sides move differently.
If you want stronger/stiffer hull sides, add another course of stitchmat to them.
If you want a 450 HP engine in an already stiff 18' boat, maybe add a couple of gussets that end a few inches from the hull sides.
If we were talking about 1000 HP, we'd be having a different discussion.