Hi, I am looking for a period-correct Buick engine swap for my '66 Skylark; something I can rebuild and get ready when my 340 eventually gives up the ghost. I think I found a pretty good candidate in a '66 425 at a local muscle car junkyard which has supposedly been rebuilt shortly before being dry stored at a body shop for some 7yrs. I have read that 401s and 425s are the same externally with the exception of some nub on the back of the block on the 425 (something used when the block was initially milled), but I can't seem to find any threads for people putting 425s into 66-67 Skylarks. I have, however, seen swaps where people have put in 401s using GS mounts; but nothing about 425s. My initial thought is that this would be a great project to rebuild and swap in but am I missing anything huge that would make this a bad idea? I know that I will need a beefier tranny, maybe need to move the cross member back, different accessories and drives, different starter, wiring harness, different radiator, exhaust, and finally new pads/mounts for the engine. On the latter note, does anybody know of a current source for engine mounts/pads? What about the Chevy 3-bolt mount, is this a sketchy idea or will it work? Thanks, Ray
MANY '65-'66 GS ONLY parts needed. Not anything hard can just get costly, $$$$$ 401/425 are a DIRECT swap. Best to use '64-'66 "NailHead" & '65-'66 TH400 or you could also use the TH300 that was originally behind the original '65-'66 GS Skylarks. Then again, many people change them out for a TH400. Tom T.
You could build a SBB 340 or sbb 300 stroker(the 300 would be better of the 2 to use) with ported TA Rover heads and a 200R4 for less $$ than finding and buying all the rare '65/'66 hard to find GS parts needed for the swap and rebuilding the N/H and sourcing a trans core. You'll also need a GS Nailhead rear sump oil pan and GS rear sump oil pickup for this swap. The battery is on the opposite side as well on the '65/'66 GS cars with a Nailhead than where your battery is now. Can't use the ST300 you have without an adapter to mount it to the N/H, you would have to find a ST400 or a ST300 with the N/H bolt pattern for a direct bolt together engine and trans combo. Depending how far you can bore your sbb block will dictate how many cubes you will end up with if you choose to do a stroker. Even if you could only go to a .030" overbore you would still be able to get the CID to 358 with a 3.990" stroke. I have heard that the sbb 300 blocks have thicker cylinder bores so if you get a block that sonic checks thicker for an .090" overbore(3.840") you would be able to have 370 cubes from the sbb 300. One of these builds with ported TA aluminum Rover heads would run circles around a 425 N/H, beating it everywhere except perhaps toque output but the extra HP would make up for it a lot. :TU: Just trying to give you another option with a path that will have less resistance. If you do find all the swap parts then a 425 would be a cool swap though. GL Derek
Well, as far as DIY power...it's a heck of a lot easier to see a 260cfm sbb head than a nail, with a step-by-step guide showing how right here on the forum.
I love my nailhead(s) but if I was starting from a Skylark I'd go with a 350/350 or 455/400 combo. Unless you find a GS for parts, much easier to gather specific parts for those swaps...
mine wasn't that bad really. I mean I have all the part I need to drop mine in except the adapter for the trans. I shop around though. I considered a 455 hard though.
