5.0 to 5.7 swap

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BrockR

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Aug 25, 2009
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28
i have been told that a 350 will directly bolt into place of a 305 was wondering if the experts here could back this up

also if the previous is true can an auto block be used in place of ive heard people talk about marine grade so im not sure

and finally if it possible to swap should a 2 bolt or 4 bolt main be used
thanks
 
mkast

mkast

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Joined
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Messages
1,934
Re: 5.0 to 5.7 swap

BrockR said:
i have been told that a 350 will directly bolt into place of a 305 was wondering if the experts here could back this up

also if the previous is true can an auto block be used in place of ive heard people talk about marine grade so im not sure

and finally if it possible to swap should a 2 bolt or 4 bolt main be used
thanks
Click to expand...

Same vintage engine will, 305 to 350.
Two or four bolt block doesn't matter, most Mercruiser engines are two bolt mains.
Blocks are the same between marine and auto, that doesn't mean, "Drop in a 350 two barrel out of a station wagon".
 
Fishermark

Fishermark

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5,617
Re: 5.0 to 5.7 swap

BrockR said:
i have been told that a 350 will directly bolt into place of a 305 was wondering if the experts here could back this up
Click to expand...

The simple answer is "yes." If they are of the same "vintage" it will be a direct swap. To ensure that they are, just make sure you have the same type - i.e one piece rear main, etc.

BrockR said:
also if the previous is true can an auto block be used in place of ive heard people talk about marine grade so im not sure
Click to expand...

The actual block and internals will be fine. If it truly is an auto block, then there MAY be a cam issue - but a truck cam works fine. The core or freeze plugs will need to be brass.


BrockR said:
and finally if it possible to swap should a 2 bolt or 4 bolt main be used
thanks
Click to expand...

Makes no difference. A 2 bolt main is plenty strong enough.
 
B

BrockR

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Aug 25, 2009
Messages
28
Re: 5.0 to 5.7 swap

thanks guys
i know about all the components that need to be marine just wasnt sure about the block the boat is a 77' and i think the engine is original not for sure yet its not mine yet looking to buy:):

so as long as they are the same vintage they will mount up the same
 
Fishermark

Fishermark

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Joined
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5,617
Re: 5.0 to 5.7 swap

BrockR said:
so as long as they are the same vintage they will mount up the same
Click to expand...

Correct. That's the good thing about the old small block Chevies - they are identical on the outside and all mount the same. (At least the common ones - like the 305 and 350)
 
Bondo

Bondo

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70,524
Re: 5.0 to 5.7 swap

the boat is a 77' and i think the engine is original not for sure yet its not mine yet looking to buy
Click to expand...

Ayuh,... You'll need a 1986 or earlier motor,... 2 pc.rear main seal...
You might run into issues with the dipstick, if block mounted,.. It swapped sides in 79...

What drive is behind this SBC,..?? Hope it ain't OMC,...
 
B

BrockR

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Joined
Aug 25, 2009
Messages
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Re: 5.0 to 5.7 swap

its a mercruiser the owner doesnt know what it is so when i go look at it i will have to figure it out he said the outdrive says 220 hp and the engine is a 305 i do not know i will find out saturday but thank you all for your help
 
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