I was chatting with someone and they said there were actually 4 different types of 401s with varying compression and hp. He said that supposedly my 66 401 with MT on the valley pan should be 340 hp as opposed to 325, and that my 63 401 might have higher compression heads. Theyre both sitting on the shop floor and before I rebuild them was wondering if I should do some interchanging to get the best motor I could using both of them? If anyone has any input or info on this I'd love some input. Jimmy
Im going to have to go to the shop and check the 63 for the code. Since Im dropping the 66 401 into a 66 skylark it probably makes sense to go with that since its a GS motor. and that way I wont have to grind the lip of the crank on the 63 to put an adapter on to put the ST 400 on. GS frame pads should be arriving this week
If you're rebuilding and replacing the pistons, it doesn't matter what code the engine is. Use the block that sonic checks the best and contact Tom Telesco(telriv) here on v8, he has the hookup for the better Nailhead pistons. Tom's pistons can get you to the compression ratio you want. Use the '66 crank with the better block, use the heads that aren't cracked and you should have a strong foundation to build upon. But make sure the '66 crank will fit in the '63 block before sonic checking both blocks though because I can't remember if they are interchangeable? GL Derek
MT was the big car designation 401 - MR was the main Gran Sport designation 400. The big cars would have a mid sump pan while you need a rear sump to fit in an a-body. Cheryl
The thrust bearing is different between 64-66 and 63-earlier. 64-66 has a wider thrust surface on the bearing, so the block is machined for that taller bearing. I don't know if the machining is different on the block, Tom should know. Just use the correct main bearing (the center thrust bearing) that fit's the block. There was a high compression 11:1 401 in 1966 but those are extremely rare.... less than 50 built. The '66 401 GS had a 340hp option that was the normal 10.25:1 cr but had different cam, distributor and carb to produce the extra hp. And there were low compression versions too. Either for export or set up with 2 bbl carbs.
The power output from YOUR build will be determined by what you do with the engine's top end...airflow, cam, compression. As mentioned, the factory differences go away when you toss the pistons, replace cam, do head work. Now the fun begins. Tear them all down and see the differences in condition and repair cost. See how much space is taken up by dismantled engines.
I've got a lip on the end of the crank on the 63. It had a dynaflow hooked up to it, so i picked up a "bearing adapter" to put on it. I just need to grind the lip off and put the adapter and a new flexplate on ( or drill the old flexplate for the new converter ) and I should be good to go on that with the ST 400. My next question is.... did the 401 A/C version come with a 5 blade fan and the 401 non A/C one come with a 4 blade? And if so would the 4 blade from my 300 work? Do I need a clutch for the 4 blade? I'll find out in a couple days when I get to the shop and start swapping stuff around, but was curious if anyone knew if ANYTHING was transferable from the 300 ci engines to the 401 / 425 ones. I'm getting nickel and dimed on this swap ( wish it was that cheap) and anything I could do to not have to buy another part would be great! Many thanks, Jimmy
I am not sure what is interchangable between the 300 and 401. It may also depend on what years you are talking about. For the 66 Skylark GS, the AC version does have a 5 blade fan with a clutch. Non AC would have a 4 blade fan without a clutch, but the pulley is also a different size to change the speed of the fixed fan over the clutch fan on the AC car. So its not as simple as jist changing the fan. You gotta have the right pulley too cause they are different.
from what I read you have low and high comp that's it. minus the super rare 50 units mentioned. the 2 bb lo comp the 2 bb high comp and 4 bbs.
The AC fan pulley is smaller in diameter so as to turn the water pump (and fan) faster. As far as I know, all late AC Nailheads use a three-groove pulley on the water pump because of (obviously) the two belts that drive the AC compressor. FWIW: The two belts aren't really necessary for the compressor, but there is very little belt wrap around the alternator in AC cars, so to get the necessary friction, two belts are used to double the amount of wrap.
i have a question about my 63 401 motors. they were in a boat and they had a big flywheel but not the same as a stick. is the cranks the same as an automatic? also when the 401 are built for racing do they beef up the lower part of the blocks like they do the 455 blocks?
The blocks are already beefy. I can't see the cranks being any different, it would be much more simple for Buick to drill a flywheel bolt pattern to match what there.
