I have a 401 that need a bore. I also have a nice set of new 425 (std) pistons, forged and fullfloating with rods Can I bore my 401 that much? Anyone that know that? Jan 66 Wildcat GS 66 Wildcat
If, at some time in the future you find a very good 425 block, you may be able to use your pistons. The forged clearance is a generally a bit more than cast, so a little honing may get you there. That said, I have generally found the nailheads that I have gone thru, to have fairly worn bores.
Jan I am in the process of getting started on a 425 and was wondering what brand the pistions are? I was also wondering if they are stock replacement wieght or a lighter one that requires re-balancing of the engine. Not sure my 425 would hone have not checked the block. Thanks Bill.
The blocks are the same , the bore on the 425 is bigger, that is the only difference. On any given engine about .060 over is the limit. Back in the'' good old days'' we could go .125 over but not with the later engines. Best to check the engine sonicly to see just how much material that you have to work with before boring. As a rule , I only bore just enough to clean up the block, because you dont pick up much power by boring. In fact , if an engine can be honed enough to clean it up to the next size that is what I do.
Really? I was told the blocks look the same but the 425 has more meat for the bigger bore. Or was someone blowing smoke up my ----end?
My block is out of a 66, so that is a "new" block. I will see if I can get a ultra sound check and take it from there. Thanks a lot guys!!! Jan 66 Wildcat GS 66 Wildcat
Hi.. new to this but trying to determine the same.. My understanding is if you have a block casting ending in 705 (which is for a 401 or 425) then my understanding this is the only block casting that will allow you enough meat after you bore the 425 std. the earlier casting were different.. can some one validate this.. thanks
Welcome aboard Kerry-I think the 704 is the 425 and haven't heard anything about late or early castings being different-they are all rather 'thin wall'-do some site searching and others will add, too-
Generally speaking 0.060 is the limit for nails. you can go over that but it gets expensive and has to be done right, not for the street car. It is best to just bore enough to clean up the cyl. and then stop. You dont gain that much by boreing.
One of the nailhead junkies on the Yahoo Nailhead Group just had a 705 block sonic tested. The max safe bore for a NON RACE engine that it would take was 0.040. He debunked the 705 myth. Go back and re-read the threads; listen to Tom Telesco. He's built more of these engines than all the rest of us combined can even dream of. I'll bet he's forgotten more than we know as a group. Ed
The 401 and 425 blocks are different castings!! This does not eliminate the possibility one could go .060 or more on a 401 block but why chance getting so close to the water jacket? Play it safe, use some common sense, and find a 425 block, Tom Mooney
The 401 and 425 are essentially the same engine...the 425 just has an eighth inch bigger bore. They both used the same crank...hence the same bore spacing. The 425 was the end of the line for that block design. Buick simply ran out of room between the cylinders...just look at a head gasket. With thin wall casting, the different block numbers represented the foundry cylinder core difference for the two bore sizes. As for boring a 401 to 425...I think Packard had the only V8 that could be safely bored an eighth over...:grin:
You can bore a 400E cid Olds used 1965-67 easily 125/1000" to 425 cid. In general you can take a 400E 125-185/1000" overbore. So that is 425-439 cid from a start of 400 cid.
No one here has brought up the problem w/ core shifting. A big problem w/ the 401's. Go w/ what Doc says and just hone it a little. Most every N.H. guru here has said to do it (go to 425)may be disasterous..... :ball:
Actually, It can be done. Lets pretend that I have mega bucks; har , har, A man could take a nail head and bore it out in every cyl enough to put steel sleeves. You might have to siamese the sleeves. but I think that it is possible and have it hold up. If I was a auto machinest or had mega bucks , like I was talking , it could be done. An over bore can go a loooong ways that way. the sleeves will not fail. I had a freind that owned a machine shop in Houston many years ago and I saw him do some engines that way, but they were race only set ups. like they[who ever that is] say; speed costs money, just how fast do you want to go???????? Now with all that said; practically, it is easier and less expensive to just build a 425 to start with. I still say bore the smallest amount possible. 0.010 over is just right, what ever it takes to make the cyl. round again and no more. that way you can build an engine more times before it is used up.
