318 to 350 swap

TinLizzy
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Location: Lake Superior-Michigan's U.P.

318 to 350 swap

Postby TinLizzy » Mon Jan 08, 2018 1:32 pm

This past year I decided to replace the original 318's that came with the boat with a couple Chevy 350's. I had replaced a lot of parts on the 318's, manifolds, electronic ign., alternators, starters, wiring, etc. The motors ran fine, but I was looking for a little more power and part availability. I ended up scrounging around and found a late 80's 350 with Marine Power trim on it. Then I found a late 80's 350 with OMC trim on it. Then the fun began. As almost all 28 express owners know, the engines are a very tight fit, much more so than the 32 ft models. I started out by yanking out the old engines, cleaning the engine bays, then tried to dry fit the Marine Power enigne to see how it fits.
First problem was the exhaust manifolds were to high and they hit the floor bracing. Then the engine mounts were not long enough and would need at least a 3 1/2" spacer underneath mount and hull stringer. The thermostat housing was also hitting the floor bracing. So, after taking some measurements, I found out that the Crusader log style manifolds would fit under the floor. I found a few older Mercruiser thermostat housings that fit, but the had 4 outlets and I only needed 2, so I plumbed the extra 2 hoses into the manifold just before the elbow. These would have been used if I had closed cooling, but I had raw water so I didn't think I needed them, but in the mean time I will leave it like this. I ordered some longer engine mounts from Marysville Marine and was able to get close to the height I needed. I also ordered another crank shaft driven raw water pump for the OMC engine to match the Marine Power. The velvet drive tranny's bolted right up to the GM bellhousings after installing new flexplates on the flywheel. Set the engines back in the hole, and see that the larger inboard oil pan was hitting the bracing on the hull between the stringers. Pull engine out again to trim off some bracing, I don't think I removed enough to hurt anything, I hope. In and out with engines a few more times to get everything fitted right. Rebuild both Rochester carbs. I am sure I skipped a few steps in here somewhere.
But the boat is now ready to hit the water. Drop it in and idle around for a little while, then put it up on plane. The old 318's would run up to about 38-3900 rpm's, at around 37-38 mph. I left the same props and shafts on for the 350's. The 350's will run up to 4,200 rpm at about 39 mph. Being that I am running the same props I guessed that my cruise speed wouldn't change much, and it didn't. I would cruise at about 2,900 rpm with the Chryslers at around 26-29 mph, this would be right before the four barrels would kick in. With the Chevy's, I can cruise around 3200 rpm before the four barrels kick in at around 31 mph.
I liked that part as I primarily take this boat over to Isle Royale Nat'l Park which is about 60 miles of open Lake Superior to get there. I only made one trip there last summer, but I was very happy with the end result. I did have one hiccup though. After the initial sea trail, we went on a 60 mile round trip overnighter. Had no problems. Then the night before the Isle Royale trip, I went to the Marina to fuel up, and as I was getting the boat back on plane, it started to vibrate real bad, I brought it back down to idle to check on engine, saw nothing, and put it back on plane. This is when it started to shake bad and then all of the sudden the engine started to free wheel. Uh oh. Blew up Tranny? Nope. I sheared off the prop shaft right behind the strut, loosing the prop also. I was really bummed because I have yet to get any spare shafts or props. I called a guy I know that has an older 28 express he wasn't using, and he gave me his spare shaft and prop. He is an AWESOME guy! So we pulled the boat out, removed the old shaft, stuck the used one in and the prop. Put it back in the water at 11:30 at night. I did a few test runs up and down the canal, good to go. After examining the old shaft, it looks like it had been half broke for awhile, and finally gave up the ghost.
Next spring I plan to get two new shafts. And after talking to a representative at Acme Props I will order up a new pair of props also. The Acme Props are designed like the Michigan wheel djx props for less than half the money. After giving him my boat info he gave me a recommendation for a prop that is different than the 14 x 12 Michigan Wheel I have on there. I will post results when I get her back in the water. Which is going to be awhile, we have got over 150 inches of snow in this part of the Upper Peninsula so far. We average 250 inches.
I will also try to post some pics of the engine swap shortly.
Rodney
1975 28 Express-Twin 350 Chevy's, Raw Water cooled
Portage Canal Waterway-Upper Peninsula,Lake Superior

martindesign
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Re: 318 to 350 swap

Postby martindesign » Mon Jan 08, 2018 1:52 pm

Nice read, Thanks. The parts availability and cost is a huge factor. I like gm products too but, the 318/360 were great engines. Some people say they were a little doggy but I didn't think so, and they were probably stronger bottom ends then the stock 350. I'll be curious as to your thoughts once u get the bugs all out whether it was worth all the work. Cool project for sure.
Machanic, fabricator, carpenter, plumber, electrician, designer, hotrod builder and glutton for punishment. :ugeek: current boat; 1969 Marinette 32 express bridge 440's
Catawba Oh

TinLizzy
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Location: Lake Superior-Michigan's U.P.

Re: 318 to 350 swap

Postby TinLizzy » Mon Jan 08, 2018 3:31 pm

I figured I have about $4 k in it right now, engine wise. I will probably have another $1000 in it with shafts and props and misc. items. Yes, the Chrysler's were great engines, after getting all the ign. issues fixed. If I could have found a pair of 360's for around the same price I might have gone that way.
Rodney
1975 28 Express-Twin 350 Chevy's, Raw Water cooled
Portage Canal Waterway-Upper Peninsula,Lake Superior

Tuggle
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Re: 318 to 350 swap

Postby Tuggle » Mon Jan 08, 2018 5:01 pm

Your a glutton for punishment, the fitment issues you discussed was what turned me back to the 318's. Are you running 71C's with 1" shafts?
"Deplorable", 1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

Leviathon
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Re: 318 to 350 swap

Postby Leviathon » Mon Jan 08, 2018 5:17 pm

Will be doing the same in the Spring. Also concerned about how this will fit and line up. "Engine Mount Length" from above is confusing me? Not sure what that means, but I will measure ahead of time to make sure it will drop right in. Did not think about the oil pan not clearing, so will look at that as well. I'm thinking wiring/ignition will be easier than before. My rebuilds were complete running engines and trannys so everything fits there. Anxious to see how it handles with a reduction gear and larger props. Also went with closed cooling.
Steve and Mary Levi
1973 32' Marinette Fisherman
Twin Chrysler 360's
El Ohssa
St. Joseph, Michigan

TinLizzy
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Re: 318 to 350 swap

Postby TinLizzy » Mon Jan 08, 2018 7:51 pm

Tuggle, yes they are 71 c velvet drives, 1" shafts. The shafts had been bent a few times by previous owners and I had them straightened a couple years ago. After doing some research and watching youtube videos, it seems like all the shafts break at the key way on either end, and are impossible to see with the naked eye until they shear off. They make a special dye and activator to spray on the shafts to find the cracks. Leviathon, I would go with the medium length engine mounts from Marine Engine Depot or from Marysville Marine, unless you have Crusader mounts, which I am not sure how they compare. The wiring matched right up behind the dash, if it has the rectangular plug behind the dash. My old ammeter wire and positive wire in the plug must have got hot in the past, as they were real hard to pull apart. I think a complete Crusader package will probably be the easiest set up to put in there. Besides the mounting of the raw water pump, which would be hard to do on the starboard engine. The standard I/O oil pan had enough clearance, but the larger inboard pan was a little deeper. All in all, doing probably 95% of the work myself, I would guess I had 100 hours in it, and lost 20 lbs. I believe I could do it now in under 30 hours, knowing all the parts I had to order and such.
Rodney
1975 28 Express-Twin 350 Chevy's, Raw Water cooled
Portage Canal Waterway-Upper Peninsula,Lake Superior

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Busia
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Re: 318 to 350 swap

Postby Busia » Mon Jan 08, 2018 9:26 pm

Been there, done that. I needed closed cooling and new engines. Found it was cheaper and easier to go with the 350 crusaders. Kept the Velvet drive 1:1 transmissions and the 1 inch shafts. Used the old rear engine mounts and the new Crusader front mounts. Any questions? Just message me. --Ed
BUSIA
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
Proud to be retired IBEW