seat of the pants difference between 401-425?

Discussion in ''Da Nailhead' started by GranSportSedan, Jul 23, 2018.

  1. is there really a seat of the pants difference between the 401 and 425 engines in stock form? I am going to do a motor for my car and set the stock original engine aside for safe keeping. I have access to a 401 and a 425 with the 425 core costing about twice as much as the 401. I have a complete dual quad setup to go on it. is the extra cost of the 425 really worth it?
     
  2. telriv

    telriv Founders Club Member

    Not really
     
    GranSportSedan likes this.
  3. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Keep shopping for a 425.. there are plenty in the yards around here still. No reason for it to be twice as much.
     
  4. $500 to much for a standard bore 425 core?
     
  5. TrunkMonkey

    TrunkMonkey Well-Known Member

    I have a 1964 Pervertable Frankenlark.
    401 (.030 over, so 407)
    OEM 2x4
    T-10 Wide Ratio
    (Strange) 3.54

    It's a head snapper, and it is a hoot to drive.
    I think there are a few things that can tip the scales one way or another and almost "wash out" the difference.

    But you will have about the same amount of fun from either the 401 or 425, all other things being the same. :)

    The $ is really all on you. You know what you have to spend, and while no one wants to spend "too much", focusing on that vs what you want out of the experience is a distraction.

    For me, money spent is money forgot.

    The question is overall cost and parts. If you can find everything for near the same money, the delta on the cost of the block in a several thousand dollar build, is really a small amount.

    I threw more money that I want to remember on things like finned bling. LOL
     
  6. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    500 for the core is a tad steep. I would price rebuild parts and check on availability before pulling the trigger on either. 250 bucks is a drop in the bucket when building an engine.

    Way back when when i rebuilt my 430 i had a choice between that and a 76 455. For some reason i picked the 430. It was a mistake. The hp level would be comparable but 430 pistons were very limited at the time, way more money and i waited forever. So keep that in mind.
     
  7. SpecialWagon65

    SpecialWagon65 Ted Nagel

    I like a 401. The heads don’t breathe that well to support more cubes, and they are
    Bulletproof.
     
    66electrafied and GranSportSedan like this.
  8. wkillgs

    wkillgs Gold Level Contributor

    In theory, more low end torque with a 425 but it won't rev as high.
    A quick calc says about 350 rpm difference at the same amount of head flow. (Edit: so if a set of heads on a 401 runs out of air at 5500 rpm, the 425 would would be hurting at 5150 rpm)

    I put a 425 in my blue '66 and it revs just fine! The big cams kills the low end street torque tho.

    There might be a difference in cylinder wall thickness, thinner in 425? But they are different castings. Maybe Tom knows.
     
    Last edited: Jul 26, 2018
    GranSportSedan likes this.
  9. telriv

    telriv Founders Club Member

    ON ANY NAIL BUILD YOU NEED TO SONIC TEST!!!!
     
  10. marxjunk

    marxjunk Well-Known Member

    i wouldnt waste money to get a 425 if there was a 401 for less...a cam change in the 401 can make the 401 work as good..besides, its been floating around for decades..the 425 doesnt have enough head flow for the CID...

    something as small of a change, a 400 turbo will make the biggest diff..i have one in my 65 GS and wow, does it wake up the 401...i mean wow...a q jet intake and better exhaust will help make up the diff..

    ive been hearing a lot of good things about hopping up a 364..a lot of good things
     
    Lucy Fair, PGSS and (deleted member) like this.
  11. Thanks guys, I was pretty sure there wasn't that big a difference and I plan on swapping in a switch pitch 400 trans and a 3.36 rear gear. not looking for a race car just nice torque that you feel when stepping on it off idle.
     
  12. PGSS

    PGSS Gold Level Contributor

    What year 425 and by core these are complete engines? Like 436'd skylark mentioned I don't think an extra $200 isn't much considering the price of the build.
    Does that 425 have the Q jet intake which is a big plus and I think the extra torque the 425 has fits the plan you want in this car. No I haven't build or modified much my 401 in my GS I had years ago to really give good advice but talking to Russ Martin a few years back hp will be bascily the same but he did say extra torque was decent.
    Tom T though should be the man to listen to as he's active and wkillgs "Walt" has both sizes running in his 66's..

    Hemming Muscle Mag's Nov 2013 issue did a very mild 401 .030 over build and it did make 500 ftlbs and 329hp without really anytime tuning on the dyno. Compression was lowered a bit also from factory specs. It maxed out the tq. at 2900rpm and the hp was all in by 3800-4000rpm! Unless your planning on porting I would think the extra ft.lb. of 425 would be a heck of 1/8 mile car and some fun burnouts..
     
    Last edited: Jul 24, 2018
  13. gsgtx

    gsgtx Silver Level contributor

    little money upfront for a block and then the same amount of money to rebuilt a 401 or 425. 20 hp and 20 lbs of torque more with a stock 425. put 2x4s and a bigger cam on a 401, with out a lot of gear, bottom end power falls off fast. invest in a little mild head work. what ever up grades you do on a 401 will also help a 425 the same, like cam, headers, bigger carb,and tranny,
     
    dual-quadism likes this.
  14. I now have both a factory dual quad setup and a Q-jet setup and a st400 case to build. if this thing is close to as much fun as my 65 GS 3 speed was i'll be happy.
     
  15. John Codman

    John Codman Platinum Level Contributor

    Just listen to Tom T. I have a 425, but that's what I found. I would have paid the same for a 401 core. Since you say you are not building a race car (neither was I), I would probably just buy the core that appears to be the best of the two.
     
    dual-quadism likes this.
  16. gs66

    gs66 Silver Level contributor

    The stick is probably still more fun Bob but you’ll be close.
     
    GranSportSedan likes this.
  17. 36threewindow

    36threewindow Well-Known Member

    I have no where near the knowledge of the other guys who have posted replies here but when I was looking for a Nailhead it just so happened that a Buick National show was in St Louis that summer. I talked to a number of fella's with Nailheads at the show and the one common complaint I heard from the 425 guys was overheating. Did not get a lot of detail as to what mods they had made but heat was their main concern.
    I went with the 401 but it was going in a 3,100 pound car (36 Buick coupe) so 445 ft/# of torque was going to be plenty. It was 97 here yesterday. Maybe not a big concern where your at - Good Luck.
    Al T.
     
  18. gsgtx

    gsgtx Silver Level contributor

    putting a bigger cam in a 401 or 425 will make them run hotter. my 401 bored 21 thousand over and stroked to 3.69 = 410 cubes and my 425 bored 38 thousand over and stroked to 3.75 = 446 cubes both run about the same degrees 183*-188*
     
  19. TrunkMonkey

    TrunkMonkey Well-Known Member

    My 401 is .030 = 407 and a hotter cam (I do not have the specs). 2x4 and 4 speed.
    160* thermostat. (Florida)
    Correct 12* distributor (with pertronix III and coil)
    2.5 pipes.

    Yesterday it was about 97* and highway (70MPH @ 3200) to stop and go the last 5 miles to the house. (45 minute drive)

    Car was running up to about 195* at 70MPH, got up to about 205* in the stop and go, and did hit 210* at the last stop light that is about a 4 minute cycle.

    This is with the GS radiator, shrouded, and about 1-2" distance between fan and radiator (engine tilt). Using an 18"- 4 blade prop.

    Hope that helps.
     
  20. gsgtx

    gsgtx Silver Level contributor

    would have run even hotter with an automatic tranny
     

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