Olds 350 vs 425

fleming442

Captain Tenneal
Supporting Member
Dec 26, 2013
13,085
113
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?
Yep. 425 all day long. It has a steel crank. Put in some light rods, forged pistons, a good balance (neutral if you can swing it), a roller, and E-brock heads with good springs, and let that mutha rock.
There's only handful of good Olds builders, so be careful.
Yeh, easy 5k... but, so worth it.
 
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UNGN

Comic Book Super Hero
Sep 6, 2016
3,048
113
Southlake, TX
A nice '85 442 with a 425 will easily be worth more than $5K more than a one with a stock 307.
 
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William

Not-quite-so-new-guy
Feb 29, 2016
32
8
You'll need to add hardened seats to the 425 heads for unleaded gas. Otherwise, the 425 is a great engine.
 
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Oct 14, 2008
7,453
113
Melville,Saskatchewan
You'll need to add hardened seats to the 425 heads for unleaded gas. Otherwise, the 425 is a great engine.
Or use the new Edelbrock heads😉. Olds heads have almost Zero issues with valve seat recession, never seen pics of sunken seats. I have never seen any issues myself but both my sets of #6 heads don't have hundreds of thousands of miles on them.
 
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Ted84

n00b
Sep 14, 2021
2
1
A nice '85 442 with a 425 will easily be worth more than $5K more than a one with a stock 307.
I have 84 hurst olds was thinking of the 425 also, but was told I'd have to get a hood scoop is this true?
 

JAMCAR223

Royal Smart Person
Jun 6, 2014
1,727
113
Houston, TX.
1" taller deck height on the 425 = 1" drop base air cleaner. Problem solved!
 

84 W40

Master Mechanic
Dec 9, 2009
416
93
I have 84 hurst olds was thinking of the 425 also, but was told I'd have to get a hood scoop is this true?
Depends on the intake your going to use. Stock 425 intake with a low profile air cleaner, no problem. Edelbrock 2151 with a low profile air cleaner no issue.
If you use an intake taller than a 2151 thats when you have a hood clearance.
Your body bushings, depending on the condition play a role on hood clearance also.
 

DRIVEN

Geezer
Apr 25, 2009
7,125
113
*CENSORED*
Toronado intakes are lower in height by quite a bit.
 
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84 W40

Master Mechanic
Dec 9, 2009
416
93
Toronado intakes are lower in height by quite a bit.
I do agree its lower in height but not choice of intake I would use.
 
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Oct 14, 2008
7,453
113
Melville,Saskatchewan
I have 84 hurst olds was thinking of the 425 also, but was told I'd have to get a hood scoop is this true?
I say Olds 350 with the 4" 4340 or 5140 billet steel stroker crank kit😁. Find some 69 5A 350 heads paint it semi gloss black and fool nearly everyone. Smaller bearings, allow tighter clearances and way lighter parts for the same 425 ci. It is slightly lighter than a 330 crank and much stronger. You need aftermarket rods and either the Mahle or DSS pistons for a proper 425 BBO build, about half way to a small block stroker. Even a drop base is needed with a RPM on a SBO. Call me the Champion of the Small Block Olds😉. You need a drop base and a 2" tall filter with Performer on a BBO in a G body. Good luck.
 
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