PLEASE help! Engine Swap Knowledge Needed!

[Korby]

Okay well I bought this boat 2 weeks ago in hopes of enjoying it with my family before I deploy in sept. The previous owner forgot to winterize the boat and crack the block. He swapped the 305 with a 350 and transfered all the marine parts to the 350. The boat was overheating and he decided to sell it. I replaced the impeller housing and impeller, thermostat, fuel filter, changed oil, and oil filter. The boat ran good for about 10 min. And my oil pressure dropped to nothing and engine started knocking. Needless to say the engine blew on my way back to the dock. I have a 400 small block that's in a old chevy truck that runs strong. Can I swap all my marine parts over to the 400 and put it in the boat. Iam looking for a quick repair due to my limited time left before I leave. I have read that 400's are not good motors to use but it is what I have and its free. Please help me. This is my first post and I am new to the boating world. Thank you.

 

[Bondo]

Re: PLEASE help! Engine Swap Knowledge Needed!

Can I swap all my marine parts over to the 400 and put it in the boat.

Ayuh,... Sure,.. I'm doing the same swap...

 

[Doernuth]

Re: PLEASE help! Engine Swap Knowledge Needed!

Make sure your not exceeding the max horsepower for your boat hull and then go for it. Max HP should be on the USCG compliance label.

BTW post pics if you can!!!!

 

[Korby]

Re: PLEASE help! Engine Swap Knowledge Needed!

Thanks for the help! I will post pics when I Get the old motor out. Is there anything I need to do/ change on the small block to make it marinized other than the obvious things like: cam, balancer, ect. pretty new to dropping small blocks into a boat.

 

[fossill]

Re: PLEASE help! Engine Swap Knowledge Needed!

I'd leave the present cam in as you wont find a marine cam for a 400 I believe, plus its out of a truck so you should be ok there.
Stainless steel head gaskets and brass core plugs and you be good to go, unless of course you got a closed cooling system.

 

[Bondo]

Re: PLEASE help! Engine Swap Knowledge Needed!

cam, balancer,

Huh,..??..??..??

The 400 needs it's Own flywheel,+ harmonic balancer as it's externally balanced much differently than any other SBC....
But that's Not really a Marine, vs. Automotive though...

It's cammed up for a Truck Now,... It'll push the boat just fine,...
Truck, R/V, or Marine are about the Same cam grinds anyways...

I have a 400 small block that's in a old chevy truck that runs strong.

When you get it on the stand, before swapping over all the accessorial marine stuff, Igntion, Carb, Wiring, Manifolds, Alternator, Starter, Etc,...
Swap in a set of brass coreplugs,... You'll need 10, 1 5/8" brass coreplugs,...
I got mine from Napa...
And,...
Unless you intend to pull the Heads,... I wouldn't worry about the Head Gaskets...
Unless if you intend to boat in Saltwater...
If you are going in the Saltwater, you'll need to swap to a set of SSteel composite Headgaskets...
I'm Not doing mine,... Not now anyways,... Not till I find a set of Votecs,+ get 'em prepped...

 

[Eric 3.7LX Alpha 1]

Re: PLEASE help! Engine Swap Knowledge Needed!

Yeah definately keep the flywheel n balancer on that 400. They also have steam holes drilled into the head and block that other small block chevys don't have, so might require a special head gasket for it if you get into the heads. The 350 heads can be drilled to add the steam holes but I've never done it. They need to be a certain dept to catch water passage I think. Machine shop could.

 

[SuperNova]

Re: PLEASE help! Engine Swap Knowledge Needed!

Yeah, the 400 is externally balanced and as such it uses a flywheel and balancer that are a little different than the other GM small-blocks. Here is the problems, however minor; if the truck was equipped with an automatic transmission, the flexplate that the engine will have bolted on the back of the crank will not work on your boat.
You will need to purchase an actual flywheel like is used with a manual trans before putting the engine in your boat. If, however, the truck used a manual trans, then you are good to go.

Even a note on the core plugs: The steel ones will work fine for a couple or three years..so short term repair-wise don't worry about them. If you think the engine will be serving boat duty for longer than that, then you better follow Bond-O's advice and swap them out while you have the engine out.

 

[Korby]

Re: PLEASE help! Engine Swap Knowledge Needed!

Thanks again for all the advice I am sure it is not going to be an easy task but maybe I will get it done before boating season is over. I am going to have to get a flywheel for a manual trans but other than that I believe everything else will bolt up. Any tips on how to make the process go smoother and easier for a first timer? Just wondering how much faster will a 400 scoot me along the water? The boat is a 20 ft Regal Valanti 200 with a after market prop connected to a merc alpha outdrive. Thanks again for all the advice.

 

[fossill]

Re: PLEASE help! Engine Swap Knowledge Needed!

I'd bet that you'll find that the 350 will have had way more power than the 400.
It will do the job but from my experiences owning both in various GM vehicles, the 350 outperformed it big time.

 

[Korby]

Re: PLEASE help! Engine Swap Knowledge Needed!

okay getting ready to tear into the 400. a friend told me to put the 350 rods in it and it will perform better. i have no clue if this is a good idea or bad one. also what pitch prop should i run for the 400. the prop thats on the boat is a aftermarket prop for the 350 i guess (thats what the previous owner told me) will it work or should i get a diff prop? like i said iam new to all of this so have patience please. the out drive is a merc alpha will it handle the 400? the 400 has a 4 barrell factory carb will it need replaced? iam rebuilding it of course but is a certain kind better than the one on it? as far as a time frame how long do you think the swap is going to take me. iam very mechanical but have never tore into a boating project like this. what about the rpms on the 400 i heard that they dont do well with higher rpms does that mean i have to run it half throttle all the time cause i wanna go fast lol. thanks for your time and patience with me.

 

[Bondo]

Re: PLEASE help! Engine Swap Knowledge Needed!

a friend told me to put the 350 rods in it and it will perform better.

Ayuh,... Don't,... The process is Much more involved than just swappin' rods...

Just swap 'em, long block for long block.... Keep it Simple for now...

also what pitch prop should i run for the 400. the prop thats on the boat is a aftermarket prop for the 350

Again, Keep it Simple for now,... Run what's there,+ see what you get for #s,... mph, rpms, etc..

the out drive is a merc alpha will it handle the 400? the 400 has a 4 barrell factory carb will it need replaced?

The Alpha will take the pressures, the 400 isn't much more Horsepower than later 350s,...
Stock that is...
The carb on it now in your truck, Ain't marine rated,... Swap it to an Edlebrock 1409...

as far as a time frame how long do you think the swap is going to take me.

Probably 100hrs. or Less...

what about the rpms on the 400

It's comfortable at 4400/ 4800 rpms at Wot...

does that mean i have to run it half throttle all the time cause i wanna go fast lol.

Nope,... If necessary, you'll adjust the prop pitch to hold the motor to the rpms I stated...

Btw,...... Ever heard of a Paragraph,..?? They would make readin' your posts Easier....