Olds 350 vs 425

sldwys

Greasemonkey
Nov 21, 2020
128
28
Ok. I’ve had my 85 442 for about two months. Driven it a few times then went straight to tune up and water pump replacement, and few other odds and ins.

At some point in future I plan to swap either a 425 or 350 in it. I’ve already picked up a 425. I have option to buy a 350.

I just want a fun street car to cruise. What motor would be easiest and cheapest to slightly build and throw a mild cam in?
 

GuysMonteSS

Royal Smart Person
May 21, 2011
1,449
113
Kentville,Nova Scotia,Canada
I'm not 100 % certain,but I believe that the Oldsmobile engines share the same size block.
If so,go as big as you can !!
Guy
 
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oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,754
113
mpls
425, more cubes = more torque = more fun.

350 sbo and 425 bbo do not share the same block but do share the same block design. bbo are 1" taller than sbo. oil pans, timing covers, valve covers, distributors will interchange. each one has their own idiosyncrasies. research accordingly.
 
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Oct 14, 2008
7,454
113
Melville,Saskatchewan
As said the 350 is a direct swap for all the 307 accessories. If you want 425ci and not have to modify the A/C brackets, get the 4" stroker crank kit for the Olds 350. The 425 is a BBO, careful attention needs to payed to bearing clearance and quality of machine work during the rebuild. There are new, ultra modern Mahle pistons and aftermarket rods that are direct fit for the 425 as well. Also the 2004R will need upgrades to live behind either motor with any kind of power upgrades.
 
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sldwys

Greasemonkey
Thread starter
Nov 21, 2020
128
28
Thanks for the replies. I’m going to stay with the 425. Already bought it and would rather have the bigger motor. Either motor would probably take 5k to build slightly above stock. Right?
 
Oct 14, 2008
7,454
113
Melville,Saskatchewan
Yes, pretty easy to spend that. Edelbrock just redid their aluminum heads as well😉.
 

sldwys

Greasemonkey
Thread starter
Nov 21, 2020
128
28
Yea I saw that. About 1k a piece for them.
I’m so new at all this, Oldsmobile and complex mechanic work but I’m learning. But I like the idea of a big block olds in my 442. May take a while to get there though.
 
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500/600

Royal Smart Person
Supporting Member
Nov 17, 2018
1,169
113
West Virginia
425 all day long.
 
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