yeah maybe . i think the 401's came with a forged crank ( wide parting line ) and the 425's had a cast crank ( thin parting line ) . also , the 425's were more limited in production and used in the higher dollar cars and they may be more expensive to purchase since they are percieved as being more valuable . small performance difference , same availability on parts more or less , maybe even a little better for the 401's due to their use in the gs's . there is probably better availability on parts now for these motors than say twenty years ago due to the nostalgia factor . not cheap - just better . QC from the factory was good on these reportedly , 64-66 may be the best years to use , some differences in the earlier years as far as parts interchange / availability . the 65-66 big cars had TH400 style trans with "switch-pitch" tq converters . alot of the guys on here can fill ya in with more details i'm sure . del
Thanks del I have been looking for a 401 with the idea of it going into my 64 lark. I found a 425 and still don't know. It sounds good and I can get it for very little, but I know little about the engine itself. It has a th400 so it must be like a 64, 65, 66 riv? I haven't heard it fire and am looking into all the info I can get.
Both engines used the same forged crank and rods. The 425 had a larger bore. They also shared the same heads. Parts are the same price no matter which of these engines you get. I would go for the extra cubes if available, but I am biased since I have two 425s and only one 401. Cherly
Talking with WildBill (TopCat) he thinks the 425 engines didn't live as long as the 401's just because its hard to find old Buicks with the ORIGINAL 425 engine. He has seen a bunch of them. That said, for what we do with them its probably not a factor (whatever it is :grin: ) SO I SAY GO WITH THE BIG CUBES! I've got both, they all run well-Ok, my one Wildcat is down on power, but I'm working on it... uzzled: I think Carmen said that the lighter cast cranks were used late in 66-not a universal 425 but kinda spotty-I've got 4 425's with forged cranks, probably all of them original to the engines. Good luck with it! :TU:
401-425 I would say very little mechanical difference, both tough, only weak point is the factory cast pistons and the harmonic balancer key way problem. The torque is the main difference. more cubes more torque. I love them all. Of course nothing looks like a dressed out nailhead, :Brow: :Brow: :Brow:
It would appear to me that the 401 has a better bore-stroke ratio than a 425. All the 401's I have played with also seem to last longer & run harder. Then again the 425 in my '64 Riv. has over 180K on it since I rebuilt it in the early 70's & has propelled my 4400+ pound car down the 1/4 at a 13.902ET. The 401 in my friend, Bob Quigg's car is the same block, crank, heads for more than 30 years. And the same with the pistons, rods, cam & standard crank until just recently when they were replaced. This combo has been good in a GS Skylark using 40+ year old technology to propell this GS down the 1/4 at an 11.08ET @ 122MPH.
Thanks guys. If I go with the 425 and it does need cylinder work will I run into any problems boring it out? Due to the large cylinder size? Or will it take a standard .30 plus some?
Any later NailHead that needs to be bored should always be sonic tested 1st. for cylinder wall thickness. In the Buick chassis manual it states to only go .010" on a 425. In the later years of the NailHead core shift was a big problem. Since the engine was going to be dropped in favor of the 400/430/455 not much was put into correcting the problem. Was also told that most all engines with little or no core shifting were usually taken off the line & given to the racers of the day.
