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Ls 5.3 into old 1975 boat

Old 02-10-2020, 08:20 AM
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Default Ls 5.3 into old 1975 boat

I've seen a bunch of builds on other forums and I've done a good amount of research. Is it even possible to put an ls1 5.3 truck engine I have laying around into place over this old old 302 188hp Ford engine? Boat is a 1975 Srv 200 amberjack center console sea ray.

It has an upgraded mercruiser drive on it but I'm not sure what else has been changed on it. It's a project boat and I want to get it back up and running like a top.

Thanks for the help I tried to upload pictures on here. My post count isn't high enough.

Thanks!
Old 02-10-2020, 08:29 AM
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Itís possible but because of the Aluminum head on a LS youíll want to run closed cooling which adds a good bit to the cost. Youíll also need to get the drive hub adapted to the LS flywheel so it can bolt to the stern drive. Also, youíll need to spend $$ on water cooled exhaust for the Ls

Not out of the realm of possibility at all but most donít do it because itís cheaper to stick with whatís already out there.
Old 02-10-2020, 08:36 AM
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You would also be looking at sourcing a marine alternator and a marine starter. I'm not sure if marine manifolds are available for that engine, I'm sure somebody here smarter than me would know the answer to that. It's really best if you can find a long block that has already been widely marinized. The 350 vortec is a good example, readily available marinized parts for them for a reasonable price.
Old 02-10-2020, 08:41 AM
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Originally Posted by Romeomikehotel View Post
Itís possible but because of the Aluminum head on a LS youíll want to run closed cooling which adds a good bit to the cost. Youíll also need to get the drive hub adapted to the LS flywheel so it can bolt to the stern drive. Also, youíll need to spend $$ on water cooled exhaust for the Ls

Not out of the realm of possibility at all but most donít do it because itís cheaper to stick with whatís already out there.
Do I need to run closed cooling on fresh-water?
And the bellhousing is not the same line up? I read on other forums it's roughly the same but it's not lining up 100% perfect(example 3 out of the 4 holes line up). The cooling on the manifolds is fine I they're pricy that's forsure.

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Originally Posted by rustybucket View Post
You would also be looking at sourcing a marine alternator and a marine starter. I'm not sure if marine manifolds are available for that engine, I'm sure somebody here smarter than me would know the answer to that. It's really best if you can find a long block that has already been widely marinized. The 350 vortec is a good example, readily available marinized parts for them for a reasonable price.
The manifolds you can buy from Hardin and they run fine with risers and manifolds. Are you talking about an older 5.7 mercruiser engine?

Would it be more plug and play with that style than a 5.3 ls1?

Thanks for everyone's help. I really appreciate it
Old 02-10-2020, 08:47 AM
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Originally Posted by Amberjack200 View Post
Do I need to run closed cooling on fresh-water?
And the bellhousing is not the same line up? I read on other forums it's roughly the same but it's not lining up 100% perfect(example 3 out of the 4 holes line up). The cooling on the manifolds is fine I they're pricy that's forsure.

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The manifolds you can buy from Hardin and they run fine with risers and manifolds. Are you talking about an older 5.7 mercruiser engine?

Would it be more plug and play with that style than a 5.3 ls1?

Thanks for everyone's help. I really appreciate it
definitely not plug and play. You are wanting to go from a Ford to a Chevy.
Old 02-10-2020, 08:56 AM
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Originally Posted by alwhite00 View Post
definitely not plug and play. You are wanting to go from a Ford to a Chevy.
Yeah changing the mount locations will be a pain but I'm good at welding. It's a project so I know it won't be done overnight. The issues I have is starting this if it's completely unrealistic. I don't want to buy a remanned block and all the other parts if I can start with this type of engine that I already have. But if it's unrealistic then I'll have to go another route is all.
Old 02-10-2020, 12:07 PM
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Anyone think a 260hp mercruiser motor would be a better idea to put in? I can get one on trade?

It should be a lot less issues than starting with a 5.3 engine from a truck.
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Old 02-10-2020, 12:37 PM
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a mercruiser wouldn't need to run closed cooling, probably a better motor for the application. The 5.3 would need to be marinized, and not sure how it would perform with the stock cam.
Old 02-10-2020, 12:40 PM
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Originally Posted by kawakx125 View Post
a mercruiser wouldn't need to run closed cooling, probably a better motor for the application. The 5.3 would need to be marinized, and not sure how it would perform with the stock cam.
So the 260 mercruiser would be the better options of the two?
I would assume the engine mounts would need to be changed. What else for the drive? The drive is an alpha mercruiser drive.

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Old 02-11-2020, 03:37 PM
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Yes the 260 mercruiser would be much easier than marinizing the 5.3 LS and much cheaper but it won't be a drop in plug and play in an afternoon drink a few beers kinda job. The old drive from the 302ci 188hp should be a 1:5:1 ratio so that would be fine for the 260hp there isn't a difference in the outdrive between a ford or chevy but the input shaft must seat properly in the coupler . Because a 302 block is dimensionally smaller than a 5.7 gm block the engine bed must be able to accomodate the 5.7 most boats not much of a problem as long as the stringers are spaced wide enough apart. In 1975 the alpha drive wasn't around yet so your drivetrain has likely seen some updating or you are looking at a pre alpha drive (just saw you mentioned that drive was changed). Pre alpha drives have shorter input shafts . When swapping it is always going to be easiest to stay with all parts from the same generation. Mismatching generation one and two alfa parts can be done but there will always be some macgyvering. Strange the LS motors have been around now over 20 years really surprised not to see more of them in marine use.
While you are at this stage check your transom condition as well as the stringers and engine bed area. Might not be worth going forward with the project if these areas need reconditioning. Whatever you think this is going to cost $$$ wise multiply that by 3.
B
Old 02-11-2020, 03:50 PM
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Put another small block Ford in it. 45 yo SeaRay???
Old 02-11-2020, 05:27 PM
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Originally Posted by brisboats View Post
Yes the 260 mercruiser would be much easier than marinizing the 5.3 LS and much cheaper but it won't be a drop in plug and play in an afternoon drink a few beers kinda job. The old drive from the 302ci 188hp should be a 1:5:1 ratio so that would be fine for the 260hp there isn't a difference in the outdrive between a ford or chevy but the input shaft must seat properly in the coupler . Because a 302 block is dimensionally smaller than a 5.7 gm block the engine bed must be able to accomodate the 5.7 most boats not much of a problem as long as the stringers are spaced wide enough apart. In 1975 the alpha drive wasn't around yet so your drivetrain has likely seen some updating or you are looking at a pre alpha drive (just saw you mentioned that drive was changed). Pre alpha drives have shorter input shafts . When swapping it is always going to be easiest to stay with all parts from the same generation. Mismatching generation one and two alfa parts can be done but there will always be some macgyvering. Strange the LS motors have been around now over 20 years really surprised not to see more of them in marine use.
While you are at this stage check your transom condition as well as the stringers and engine bed area. Might not be worth going forward with the project if these areas need reconditioning. Whatever you think this is going to cost $$$ wise multiply that by 3.
B
Originally Posted by billinstuart View Post
Put another small block Ford in it. 45 yo SeaRay???
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I really don't want another Ford engine I am running this engine and checking it out this weekend. I have a friend who works at a marina on engines and drives so we will check the damage this weekend. I have my eyes set on a 260 mercruiser right now with low hours. That will be the direction we will go in. So functionally it will work I just need to look at the space between the stringers and where the input shaft lines up. I will take some measurements when I get the chance and update everyone on it.

I believe this boat was redone at one point because I checked the stringers and transom and everything is still solid. I even took a screw driver and tried to push through the bottom of the stringers and it was as solid as can be. Which is hard to believe on a 45 year old boat. However the boat was inside most of its life and from what I was told it wasn't left in water for more than a couple of days at a time.

I don't mind projects and I have no cap. I'm just trying to redo the motor and inside for roughly 5k at most otherwise I won't recoup my costs. The motor is around 1500-2000 which isn't an issue. And the drive I can get for really cheap if needed. I will upload all the details and project once this weather breaks for spring.

Thank you all for the input and suggestions it goes a long way.
Old 02-11-2020, 07:52 PM
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My son did a swap in his 4winns. We had to drill now bolt holes in the plate, add manifolds, install a heat exchanger. He decided to run a HD electric water pump for cooling . It’s hooked up to a valve duo prop drive. Runs great.
Old 02-12-2020, 05:23 AM
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This is wrong on so many levels. Where ya gonna get marine approved parts? Software? Catalytic onverters?

But hey..go for it.
Old 02-12-2020, 05:38 AM
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So right on so many levels, another thing to be aware of is the transom assembly. Hard to see without taking them apart but they corrode from the inside out. Since your motor is out I would remove and rebuild it outside the boat all new bellows gimbal bearing and shift cable. Don't let they naysayers discourage you. I recently purchased a 2006 low hour boat to transplant the drivetrain into a 1966 B-20. He doesn't need software or emissions. The drop in motor will already have marine approved parts, essentially the carb, starter , distributor and alternator.

302 blocks didn't make all that great marine engines in the long run,The thinner wall castings internally coupled with raw water cooling lead to an earlier demise. But they are more compact so fit in tighter spaces and are in the beginning sweet lil runners. The 5.7 260 hp you are leaning toward is cheaper to get parts for than most any marine inboard. Easy to build to well over 300 hp too.
If I were in your shoes I would chose a 5,7 too but make sure my transom assembly, out drive, transom plate, bell housing , coupler, engine and manifolds were all from the same era. It just makes it easier as the early transom plates had wider spacing on the transom plate mounts, couplers differ, etc. I like the newer alpha gen 2 components and updating to it will net greater resale on the backend. It's not all that expensive and hard to come by either as the gen 2 to present has been around since late 1993.
B

Last edited by brisboats; 02-12-2020 at 05:49 AM.
Old 02-12-2020, 05:41 AM
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Originally Posted by billinstuart View Post
This is wrong on so many levels. Where ya gonna get marine approved parts? Software? Catalytic onverters?

But hey..go for it.
no cat needed and software is readily available
Old 02-12-2020, 05:58 AM
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Originally Posted by billinstuart View Post
This is wrong on so many levels. Where ya gonna get marine approved parts? Software? Catalytic onverters?

But hey..go for it.
Plenty of marine stuff available for ls engines. Pretty much every 2nd person can tune them also. No cats needed.
Old 02-12-2020, 06:01 AM
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Do yourself a huge favor and just replace the 302 with another one. You may think a swap to a different brand of power seems simple,but it won't be unless you get a drop in power package with every part on it.Mabbco Motors has reasonably priced short or long block 302's for well under $2000.
Old 02-12-2020, 06:45 AM
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Around me it's not all that hard to find parts for engines. I could buy an entire boat and swap the package over to this one. But it's really about the ability to upgrade engines. I want to do it right the first go around. It seems no different than a car, I have to swap over everything that fits that power package. Seems legit to me. I'm most likely running the 260 mercruiser engine for simplicity reasons and because it's more of a "plug and play" But it would be amazing to run a 5.3 truck motor since its all rated for heavy torque and motors are constantly available. A ton of jet boats run them around here with raw cooling so it's not out of the norm. But to make it work might be way more expensive in the long run.

The outdrive is most likely a pre alpha, but I can buy an alpha setup and run it. The bellows are all solid on here, I want to run a better engine thats faster than the old ford.

Really what else is needed on the mercruiser swap? I want to make a nice list.

So far:
Engine mount relocation brackets
New electronics
New outdrive (possibly)

But I really do appreciate everyone's input. It makes me excited to get this project started that forsure.
Old 02-12-2020, 06:46 AM
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Originally Posted by brisboats View Post
So right on so many levels, another thing to be aware of is the transom assembly. Hard to see without taking them apart but they corrode from the inside out. Since your motor is out I would remove and rebuild it outside the boat all new bellows gimbal bearing and shift cable. Don't let they naysayers discourage you. I recently purchased a 2006 low hour boat to transplant the drivetrain into a 1966 B-20. He doesn't need software or emissions. The drop in motor will already have marine approved parts, essentially the carb, starter , distributor and alternator.

302 blocks didn't make all that great marine engines in the long run,The thinner wall castings internally coupled with raw water cooling lead to an earlier demise. But they are more compact so fit in tighter spaces and are in the beginning sweet lil runners. The 5.7 260 hp you are leaning toward is cheaper to get parts for than most any marine inboard. Easy to build to well over 300 hp too.
If I were in your shoes I would chose a 5,7 too but make sure my transom assembly, out drive, transom plate, bell housing , coupler, engine and manifolds were all from the same era. It just makes it easier as the early transom plates had wider spacing on the transom plate mounts, couplers differ, etc. I like the newer alpha gen 2 components and updating to it will net greater resale on the backend. It's not all that expensive and hard to come by either as the gen 2 to present has been around since late 1993.
B
Ford engines hold up as well or even better than GM engines in raw water. They all use thinwall castings, but often the cast iron in Fords is better. Automotive fuel injection is not marine rated.

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