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330 to 525 swap opportunity

Old 12-12-2020, 02:30 PM
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Default 330 to 525 swap opportunity

Hi all,
I have a friend that is putting in new 525 blocks in his boat.
I could get one of his old 525s for 2500$ canadian. (engine in runing condition)
To put you in perspective, in my area, a used 500 carbed motor with a cracked piston is for sale as is at 4.5k$

My boat currently has a 454 carbed engine.(non mag)
I would be receiving the 525 as a longblock.
From my research these are 502 bbc's, so im guessing mechanically it will bolt up in the same space as my 454? if not this might be deal breaker.
The heads are my next concern, are my current imco powerflow manifolds compatible. is the mercury intake the only fit?

In a perfect world i am looking at a engine/head refresh, performance intake, stand alone ecu with supporting mods. Am i dreaming?






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Old 12-12-2020, 02:36 PM
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If the 525 still has the Edelbrock Mercury aluminum heads your exhaust wont bolt up, its a propitiatory bolt pattern designed around the CMI headers
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Old 12-12-2020, 04:02 PM
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Originally Posted by F-2 Speedy View Post
If the 525 still has the Edelbrock Mercury aluminum heads your exhaust wont bolt up, its a propitiatory bolt pattern designed around the CMI headers
It does have the original heads, i was looking into this and found that stainless marine offers a jig kit to drill and tap the correct bolt pattern, im guessing the machine shop doing the head refresh could handle such work. 750usd for the jig + labor still cheaper then cmi headers and exhaust. Still a setback tough.
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Old 12-12-2020, 04:18 PM
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Originally Posted by BlueAndWhite View Post
750usd for the jig + labor still cheaper then cmi headers and exhaust. Still a setback tough.
Find a cheaper way to get (reliable) 195hp out of your 330..... You can always recoup some from selling the jig
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Old 12-12-2020, 04:27 PM
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Originally Posted by BlueAndWhite View Post
It does have the original heads, i was looking into this and found that stainless marine offers a jig kit to drill and tap the correct bolt pattern, im guessing the machine shop doing the head refresh could handle such work. 750usd for the jig + labor still cheaper then cmi headers and exhaust. Still a setback tough.
How many hours are on the 525's ? your 2,500 equates to around 1,950 usd ......if so thats cheap for a gen 6 525 long block
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Old 12-12-2020, 05:53 PM
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Any competent machine shop should be able to drill and tap the heads without much more than the header gasket. You may even find a jig here on OSO.
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Old 12-12-2020, 06:12 PM
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I had to relocate the exhaust holes on my transom and the analog gauges will not work without new wiring harness. Those were the main problems I had when swapping out my 496 for a 525.
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Old 12-14-2020, 11:34 AM
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Isn't the cooling system plumbing different on the 525 head with a coolant passage at end vs the 330 if he's using his accessories? I assume this has to do with the closed cooling set up on the 525.
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Old 12-14-2020, 11:52 AM
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Originally Posted by Donzi1979 View Post
Isn't the cooling system plumbing different on the 525 head with a coolant passage at end vs the 330 if he's using his accessories? I assume this has to do with the closed cooling set up on the 525.
I doubt the long block will include the heat ex changer ? you can install freeze plugs in the heads to block the coolant passages
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Old 12-14-2020, 12:16 PM
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Originally Posted by Baja Rooster View Post
Any competent machine shop should be able to drill and tap the heads without much more than the header gasket. You may even find a jig here on OSO.
When I replaced my CMI's with Stainless Marine exhaust, SM loaned the jig to the shop doing the install.
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