hi gang, well here goes i have all ready spent too much money to back out and i need some help with motor stuff. is the 425 kinda like the chebby 400 wheras its at it maximum bore? and not much room left? i can bore out a 401 .60 and that gives me what? i only used the chebby as a point of reference in block boring can a 401 be bored as big or bigger than a 425? or is it more than that? i have a very nice 63 rivi and i want the best for it that i can put together not a #s car at this point but it was, so all complete and not wooped out i know about thelater motors fitting to a th400 so the block has to be newer than 63 but what is the best yr for the 425 thank you in advance for your help,:beer :eek2:
Craig, A .060 over 401 is a 413. The 425 can be bored, It depends on what you are going to do with it. Years ago we ran a .040 over 425 with Jahns forged pistons, I put over 100,000 miles on that in my GS, never had a problem with it. I would have no problem with taking a 425 to .030 or .040 over, even on a hot street motor. You will want a 64 to 66 425 in order to use the t-400 trans, you can use an earlier engine if you swap the crank or there is an adapter for the earlier crank for this application. I have heard some 401's can be bored to a 425 bore, but I have never myself seen one with enough cylinder wall thickness to do it. Jim Burek P.A.E. ENTERPRISES
The 425 is cast with larger holes so if you bore a 401 out to a 425 (yes it can be done) you will have thinner walls than a true 425. Hope this answers your question, Good Luck!
Oh yeah and it's not the block on 63 and earlier motors, it's the crank that's different. The back of the crank fit's the Dynaflow Converter and won't fit a 400.
I've heard it from several knowledgable folks that the 401 should only go to .060. One guy talked about core shift in the block casting. I don't know about that, but considering that all of the heads and manifolds interchange, it makes sense that a 401 could be bored to 425.....If the 425 block was cast with significant differences in the outside diameter of the cylinders, the water jackets would have to be smaller and prone to overheating, etc. I'll also bet that the 425 block is lighter than the 401. Dan
Whether or not parts interchange has little to do with how much an engine can be overbored. Lots of engine families have interchangeable parts, but that doesn't mean you can bore a Chevy 305 out to a 350 or a Ford 390 out to a 427; it doesn't necessarily mean you can't either. The main thing to look out for when overboring is, like Jim B. said, cylinder wall thickness. From what I've read (much of it on v8buick.com), core shift DOES matter when overboring, as I believe it can affect cylinder wall thickness. As far as overheating goes, the bigger cylinder won't necessarily cause a problem either. I'm no expert, so I wouldn't know whether or not the 425 does have an overheating problem, but I would assume that the engineers would have taken all of those differences that you mentioned into consideration all those years ago when they designed the 425. A 425 won't necessarily be any lighter either, if the two engines both have similar wall thicknesses. Not trying to be a dick, just trying to help clear things up. Brien
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=34202&item=1875450737 Here is what a current seller put in his description of his MT 401 block that he is selling... a 425 has a 4.3125 bore a 401 has a 4.1875 bore a difference of 0.0125 - that's a lot of boring. I wonder how many blocks have successfully been bored this far? From what I read on this and other boards, this question has been been debated many times and the general consensus is that you most likely will not be able to bore the majority of 401's to a 425. I would be tempted to sonic test it and see because if I could, I know I would. Question. What is the maximum safe thickness of a bore?
how about looking at this another way, in stock form what is the out put for a 66 401 and a 66 425 single 4bbl not dual quads? if all you have is a 401 but you would like to pursue a 425 how might i find a block and are the heads interchageable? are the 425 heads bigger valves? any better or worse? i fix cars real good but knowlegde on these old motors i dont have , out side of what i have done to mine and that was nothing big. standard .60 bore stock pistons and balancing and porting the heads as much as i dared . :beer :grin:
For '59 - '66, the 401 was 325 HP, 445 lb-ft; the 425 was 340 HP, 465 lb-ft. These were for 'normal' engines, not counting exceptions like the Super Wildcat 425 (4x2, 360 HP) and the '66 GS 401 with 11:1 and QJet (353 HP?). Heads are interchangeable and valves are all 1.875 intake, 1.500 exhaust.
Cylinder Wall Thickness ? The 401/425 cylinder wall thickness question came up on the Nailhead site a few years ago. One of the members had several 401 and 425 blocks and measured the distance between the outside cylinders walls in the water jackets with a feeler gage. The 425s had considerably less distance between the cylinders then the 401s. This supports the idea that the 425 casting core had larger internal and external cylinder diameters then the 401 even though the external casting was the same for both engines. With that in mind, boring a 401 to a 425 would be very difficult, if not impossible. Cheryl
While we are on a general 401/425 thread I'd like to ask what are the suggested head modifications for a Nailhead 80/20 (80street/20strip) engine? And we may as well talk a little about what cam is best for this application. Heck, we may as well go into the entire in's and out's of building a 'super street' nailhead. I'm sure it's all been covered before on the internet but to have all the info in one thread would be neat.
401 CI to 470 CI on: Dec 8th, 2002, 10:53am Quote Modify -------------------------------------------------------------------------------- There is no substitute for CI. 1966 GS special edition. (Dialups beware) Engine pictures. Before. http://www.sirgalahad.org/tyler/Buick/FF03_Before.JPG Pistons. http://www.sirgalahad.org/tyler/Buick/BuickMotor11.JPG http://www.sirgalahad.org/tyler/Buick/BuickMotor10.JPG http://www.sirgalahad.org/tyler/Buick/BuickMotor7.jpg Bottom end. http://www.sirgalahad.org/tyler/Buick/BuickMotor1.jpg http://www.sirgalahad.org/tyler/Buick/BuickMotor2.jpg http://www.sirgalahad.org/tyler/Buick/BuickMotor9.jpg Top end http://www.sirgalahad.org/tyler/Buick/BuickMotor3.jpg http://www.sirgalahad.org/tyler/Buick/BuickMotor6.jpg Heads. http://www.sirgalahad.org/tyler/Buick/BuickMotor4.jpg http://www.sirgalahad.org/tyler/Buick/BuickMotor8.jpg Pan. http://www.sirgalahad.org/tyler/Buick/BuickMotor5.jpg Done. http://www.sirgalahad.org/tyler/Buick/FF01_After.JPG For: John Lane http://www.sirgalahad.org/tyler/Buick/FF11_After.JPG 66 GS Flint Flier http://www.sirgalahad.org/tyler/Buick/FF10_After.JPG
Sorry don;t know anymore than whats posted I came across this on the GSCA board it was posted by a John Lane from Fort Mead Flordia I just thought it would be useful.
401 425 I'm glad there are people out there with nailhead knowledge. Thankyou for letting me pick your brain. I guess the best way to find out is to sonic test or to bore a block and find out the hard way. Its hard to find nailhead parts these days. 425 blocks are rarer than 401s around here it seems. I know the 401 will put out the power. No question about that. I know a 425 will be that much better. It really no big deal. I just like the sound of more displacement with out spending big $ on it. Nothing like the sound of a nailhead about 6 grand headed down the strip. Thanks again fellows.
