401 vs 425

Discussion in ''Da Nailhead' started by KDML, Nov 7, 2009.

  1. KDML

    KDML Well-Known Member

    Is there anything externally different between a 401 and 425? I am thinking of swapping my 401 for a 425 to gain the extract cubic inches, but I would like to reuse all of the accessories off the 401.

    In addition, is there any better year 425?

  2. Poppaluv

    Poppaluv I CALL WINNERS!!!

    Nothing different between the blocks externally. Just not a good idea to bore a 401 due to core shift issues. Send the 401 to me and have at it!!!!:TU:
  3. Junkman

    Junkman Well-Known Member

    Externally, you can use alll of the accessories on a 425.
  4. KDML

    KDML Well-Known Member

    Thanks for the responses.

    I just bought a 65 Riviera project. I would like to make some modifications including squeezing more power from the engine. I figured I might as well start with some extra cubic inches.

    I will be keeping the 401 for the future when numbers matching might mean something to me.
  5. John Codman

    John Codman Platinum Level Contributor

    Yup, bolt in and race. The only difference would be the flywheel/flexplate. They will interchange, but may be balanced differently.
  6. doc

    doc Well-Known Member

    A .040 over bored 401 is 410 cu. in. or so.... you dont pick up that many cubes by over boreing....
    Bottom line is this , if you have a choice between building a 401 and a 425 , do the 425... but other wise I would not worry about it...
    You can make up the difference in power by fine tuneing the 401, cold air, recurve dist, ''Doc dual plane'' intake manifold mod... bigger carb,,,, ect.... none of which is expensive but brings a good return in power for the money and effort.....
  7. nailheadnut

    nailheadnut Riviera addict

    Dear ?????????

    You don't say what year 401 you're dealing with and what transmission is hooked to it. Be aware that between the '63 and '64 years, the hub on the crank was changed. That would be the only difference you might have to consider if you're stepping up from an 63 or earlier 401 to 64 or later 425.

  8. roostriz

    roostriz Well-Known Member

    I thought I had read that the 401 was a better engine to modify for power due to the already anemic heads. Yes/No?
  9. 1967GS340

    1967GS340 Well-Known Member

    That's the part that I was going to mention. Get a 64 or later engine or you have to just buy an inexpensive bushing for the end of the crank to hook up to a later transmission.

    Doc, the only problem with that reasoning is that you can do all of that to a 425 and start with more cubic inches!

    I'm kinda old school when it comes to engines. After you narrow it down to your engine choices, stout and bigger are the two most important things to figure when you have to make a choice!
  10. doc

    doc Well-Known Member

    Hmmm, I see You guys did not read all of my post....:laugh: :laugh: i said,,,,'' if you have a choice do a 425'',,,,,:grin: :grin: buttttttt, If all you can find is a 401 ,,,, you can make up most of the difference with mods....and that is based on having both engines in my cars....But with both engines ,,, they are torqers.... and torque is what moves cars... not hp,, not rpms,,, and a 401 has plenty of it,,,, but a 425 has more....but not that much more....now,,,, all that said, Both engines have ample power to move a nearly 5000 lb. car to 120 mph,,, and do not run out of steam untill you get above 5500 rpm...then the heads get restrictive.... but untill that point the nail does just fine....:Brow: :Brow: now this is where mods come in,,,, mods dont change the amount of power much,,, [by power, I mean hp/torque.] but they do greatly change how quick the given engine will get what power it has....:Smarty:
    Now , where is my 3 barrell....???????:laugh: :laugh:
  11. 1967GS340

    1967GS340 Well-Known Member

    Just messing with you Doc!
    You know that I'm keeping the 401 option open in the back of my mind, not that it's going to happen, but keeping the option open.

    Both are great engines and the 401 would be my second choice for a cool power plant also. WAY easier to come by and cheaper to get one because it is so much more plentiful.

    As for the three barrel... hmm... If I wasn't going to use 4 barrels it would mean that I found a 5 barrel!
  12. doc

    doc Well-Known Member

    Uhhuh, I see that disease You have is getting worse....:laugh: it aint my first rodeo, i have been messed with before....:laugh: :laugh:
  13. CameoInvicta

    CameoInvicta Well-Known Member

    I'd rather have a smaller cube 'Nail. The heads are already asthmatic, and by having more cubes it brings the powerband down a decent-good amount. A 425 will make more low end torque, and will probably crank out a few more HP, but will drop off faster than a similarly built 401. That's just my 2 cents. I'd love to see what a built 322 or 364 could do.
  14. doc

    doc Well-Known Member

    Well, there was just a article in one of the rod books where a 364 put out 366 or so hp.....I remember back in 57 when chevy got 283 hp out of 283 cubes and every body thought it was the end all....
  15. KDML

    KDML Well-Known Member

    Thanks again for all the information.

    I just acquired a completely stock '65 Riviera with its original, but tired 401. The only reason I am considering another engine is because I don't want to take a chance ruining the numbers matching 401 (I expect in the future this may mean something to me) and don't want to retrict my imagination as I expect to make modifcations as the build progresses. If I am going to start with another engine, I figured I might as well go for the extra cubes of the 425.

    At this point the restorer in me is fighting with the customizer in deciding a path for this build. Winter is coming for me in VT so I probably won't start in on the build until the spring, which gives me much time to work out a plan.
  16. kilkm

    kilkm Well-Known Member

    Talking about the difference between the 401 and 425 - I've always wanted to put the 2X4 set up on my 401. Did only the 425 came from the factory with the 2X4 option? Any of you have this set up on a 401? Any major modifications necessary? I've wondered about distributor/timing. This is a '62 model, the factory timing in the book is at 12 BTDC same as some of the later model 425's with the 2X4. The nailhead with the 2X4 setup looks so awesome, I'd really like to do this.
  17. 1967GS340

    1967GS340 Well-Known Member

    Give in to your inner hot rodder! Custom is cool.
    425 with at least two carbs.
    Despite what one odd man out would tell you, stick to even number of barrels!
    2 x 4 or a six pack.
    Would two 3 barrel carbs be a six pack??
    Do you run on a one barrel then "kick in" the three barrels? Hmmm...... Sounds as odd as the chevy 5 cylinder engine to me.
  18. doc

    doc Well-Known Member

    Actually, There was a ''export kit'' that was available over the counter at the Buick dealer.... that had the 091 cam,lifters, 2x4 castiron manifold, 2-4bbl carbs, chrome dual snorkel air cleaner, fuel lines , progressive linkage, and I think the alluminum rocker arm covers..... Its been a lot of years and I have been thinking about my 3barrel:Brow: :Brow: :laugh: :laugh: I do remember that back when I was making $32 a day the kit was $1200.00.... but the kit was available for the 401 and 425.... meaning that any 1959-1966 Buick with the right engine could have this kit installed by just walking into the dealer parts dept. and ordering it.. and installing it your self....I did go in and order the cam,lifters and then because the 3 barrels were the new hot set up , i put one on the car instead of the 2x4 set up....but I did not do the ''Doc dual plane'' thing untill a couple of years ago... dont know why I did not think of that before then.....:rant:
  19. nailheadnut

    nailheadnut Riviera addict

    The 2x4 manifold is a bolt on for any 401 (same deck height as the 425), except that if you're running OE carbs, the kickdown linkage on anything 63 and prior will take some work. The OE kickdown for 64 and later is electronic, and the 63 and prior is mechanical. You'd have to come up with a different way of activating the mechanical kickdown on the 63 and earlers "Dynaflushes."

    What kind of performance is your Dynaflow going to give compared to the same engine in front of an ST400 switch-pitch?

    To get the same CFM from a 3X2 "six pack", you'd need three carbs whose total CFM would be 1250 (that's two OE four barrels at 625 each.) Holley 94's and 97's (three bolts to the manifold) flowed about 150 CFM's and the Rochester 2GC (four bolts) as was found on the GTO's flowed about 350. Even with three of the 2GS's, you'd still be a couple of hundred CFM's shy of the OE 2X4 set up. The Holley 2300 carb as used on the '67 Corvette flowed 500 cfm's, but they won't bolt to any existing 401/425 3x2 manifold:Do No: .

    I have a friend on Arkansas who runs two 750 CFM's Carter 9000 Comp Series AFB's on his '64 425 and he says he could handle even more.

    What you need to find is one of the old Offenhauser 2X4 manifolds that took two Rochester Quadrajets - that would give you 1700 CFM's Or 2000 cfm if you put two 1000 cfm Carter thermoquads on it.:beers2:

    Distributor timing is different with a 2X4 set up because it used a completely different distributor.

    Sonic test your 401 and you can safely bore it .060" over; yields 413 cubic inches.
  20. John Codman

    John Codman Platinum Level Contributor

    A 100% efficient 401 will flow 696 cu ft per minute at 6000 rpm. It is possible to exceed 100% efficiency, but you will need a blower to do it. Under the same conditions, a 425 needs 728 cfm. I will probably put dual Quads on my 425 nailhead powered Chevy pickup someday, but it will be strictly for looks.
    Frankly, I find it unlikely that a normally aspirated nailhead will flow at anything near 100% efficiency at 6000 rpm.

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