Hey guys, just wanted to know what yall thought about my engine choice: I dont have much experience with olds motors... I currently have an olds 455 in my 52. I just bought a 425 at a swap meet with tranny for cheap (thought it was a 455). The only reason I bought it was for the intake (offenhauser). Should I rebuild the 425 and for when the 455 dies (could be soon). Or sell it and use the money to rebuild the 455. 455 Is a 1972 with smog heads 425 is a 1965 with better heads seems to be in pretty good shape.
Price the rebuild kit's for each motor. The 455 will run unleaded right now. The compression of the 425 may be 10:1. stock. the bigger is better vs the older mill is a tough one. Are you sure the 425 is good to go?
Havent taken the heads off yet, took the intake off and it looks really clean, rockers and pushrods very clean,(i guess that could be a bad sign if they're too clean
Having been an Olds man for a number of years, I personally like the 425. The rod length to stroke ratio is the best combination of all the big block engines of all makes. They will last longer, run stronger, have better cruising range, and cost the same in terms of a rebuild. the 45 degree lifter angle is no problem and the larger diameter lifters offer better cam lobe ramp possibilities. If you don't like the 45 deg, use a 455 block with the 425 crank and rods. Give it marginally high compression, 9.0 to 9.5, and a cam with around 112 lobe separation and you will be pulled down in your seat every time you stand on it.
I would stay with the 455......less hastle to rebuild, and no surprised when you go to put it back in.... JMHO.. Let us know what you do....
Steel crank in the 425 and shorter stroke. If you were closer I would be glad to trade a 455 runner for the 425. The blocks are the same externally so no hassle to run the 425 and it is definately not a smog engine. Check if you got a Toro engine, if so you have the big valve heads. What letter is on the heads of the 425? If it is an "A" those are reputed by Bill Trovato to be the best flowing stock heads , he has an 8 second Olds so he should know. The A heads may have a one year only rocker setup. If you have a Toro engine it will run the large lifters mentioned in an earlier reply and would be the "modern" cam bank angle. If non Toro it will be small lifters and the different cam bank angle. Also if a Toro engine the 425 was pretty powerful stock with high compression. The color of the block may be a clue to what it is although paint is cheap. I think the shorter stroke will make it rev a little higher/quicker. If you decide to rebuild the 455 use the steel crank and the heads from the 425, just open the pushrod holes to compensate for the different cam bank angle.
Look close at the tranny, it could be a variable pitch TH400, made 65-67, best tranny out here! If it has short splines at front of stator support and a two prong plug on l/h side it is a var/pitch...don't let it get away! It can have one of two converters:8-2,800 stall or 8-2,400 stall.
listen to the Olds racers! We found the 425 lasts longer (breaks less) and runs as hard as the 455. The few extra cubes don't make a difference as the HP limit seems to be the heads. My Dad and I learned long ago not to use Chevy or ford logic on an Olds, they are another animal.
As '42 Chevy and oldspert stated, All 425's have factory forged cranks, wheres as only a very small handful of 455's made in '68 ONLY (from vehicles with 2BBL/tow packages) came with the rare forged 455 cranks. In your case, the 425 should be 10.25:1, compared to what I'm assuming is a like a 9-ish:1 455 with smog heads. In performance terms, once you start replacing most of the stock parts, the numbers between the 2 motors become a wash as to which one is actually better. Between your 2 relatively stock motors, your particular 425 has the edge over your 455. I'm running my 455 in to the mid-11's but here, the 425 gets my vote!
The first question you need to answer is, how do you plan to use the motor and car. Everyone is worried about forged crank, rod to stroke ratio, etc. The reality is that for a mainly street driven car, you'll never see the difference between the two. The 455 is marginally less expensive to build due to the better availability of pistons. If the 425 has the oddball 45 degree lifter bank angle (instead of the 39 deg angle used on all 1968-up Olds motors) then that cam will be more expensive also. Same thing if it has the 0.921" lifters (most Olds motors use 0.842" lifters). Other than that, most of the rebuild parts interchange between the two motors. Note that the 64-67 Olds motors (including this 425) have a different crank flange bolt pattern than the 1968-up motors, so a 455 flywheel won't bolt to a 425.
Change my vote to both,half and half.455 short 425 top with Offy on top.What size chamber from 425 to 455.Cam choice for late block more grinds.Measure the cranks,which one needs grinding ?Put smog exvalves in the old heads.They live better with the junk fuel.suond like a fun couple of weeks of wrenching to me.Win Win .
Some more info on the engines: 425 is a D block with B heads Has th 350 455 is a 72 block with J heads (has th400) not planning on racing it, would rather it be dependable...
455 is plenty fun for the money... use the 425's steel forged crank in the 455 and you can find a set of "C" heads or a pair of Edelbrocks for an awesome combination!
1973 and newer 455's have hardened exh. Vale seats for unleaded gas. 72 and older and all 425's didnt and you cant run unleaded gas in them without modifying the heads. Both are grear engnes but dont like hi-rpms.
I miss my BBO Roadster... not my fastest due to the lack of traction... but the Most fun! <iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/h29PGmIeTzk" frameborder="0" allowfullscreen></iframe>
My vote is the 425 too. I've seen a few 455s that wouldn't scatter poop but never saw a 425 that wouldn't melt a set of tires off a big old delta 88. I like Olds short stroke big blocks though.
The 455 will be a lil cheaper. no need for steel crank etc. for a street peeler, the J head with a lil cleanup work will be fine . a pretty basic rebuild with a few tips and decent cam and that thing will run strong for many many years . It lasted 30yrs already without a bunch of fancy shit and gimmicks. Give us an idea of what you want it to do and we can start giving specific ideas on how to get it . D block w B heads is 66 425, it has 45* bank cam. Sell off crank rods and heads to help finance the 455 . I start a shitstorm everytime I say it but I continualy feel the need to steer Oldsmobilers straight without breaking the bank ,so be careful with the self proclaimed experts that "specialise" in Oldsmobiles, they are in it for profit not the love.( Is that PC enough for you guys ? )
I forgot what year Toro but one of the motor options included a 400 horse motor... I think it was in '68 or '69. I'm sure it was one of those W- coded options that Doctor Olds dreamed up...
There are a few folks here who don't know the details of Olds motors. Use the 425 crank in the 455 block? Guess what. You get a 425. You also need to use the 425 pistons and rods because the shorter stroke motor has longer rods and a different compression height on the pistons. Both motors have the same 4.125" bore. Use the early heads on the 455? So what? All big block Olds heads have the same 80-ish CC combustion chambers. Olds varied compression with the size of the dish in the pistons, not the chamber volume on the big blocks. Use the heads with the bigger valves (2.000/1.625 vs. 2.070/1.625). As I said before, the 455 is marginally cheaper to build (like 10% difference) and either one is fine for a street-driven application.
I'm not an olds experet by no means but I would overhaul the 425 and when I was done swap them out. It should be healthier out of the box than the 455 Wheezer motor. '70s smog motors are just not a good choice when it comes to performance.
if i remember right the bore between the 425 and 455 is the same, but the stroke on the 425 and pre 68 400 is 3.975. the 68 400 and the 455 have a 4.250 stroke.
I'm not sure on the big blocks but I know the 350 olds engines had thermactor "bumps" in the ports on later versions that the earlier ones didn't have.
Build the 425 and sell the 455 to a guy needing one for his jetboat....as they are always blowing them up....
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