Can anyone out there tell me if the outside diamensions on a 425 cu.in. nailhead are the same as a 401 cu.in . nailhead. Also are the exhaust and intake manifold interchngeable? I have a 401 in my model A and want to step up to a 425. Thanks
The exterior dimensions are the same. The intake and exhaust manifolds will fit on the new motor. Your swap will be a "remove and replace" deal. The appeal of being able to say you have a 425 over a 401 is obvious. You my want to do some research and determine whether the incremental increase in performance is worth the cost and effort. Please indulge my unsolicited advice. Good luck with your project.
Thsnkd for the info. I believe that the LX series 425 has 360 HP, wheras my 401 has 325 H.P. I may be wrong though.
Mctim,thanks for pointing out my omission. I completely forgot about the change from the Dynaflow crank pilot to the 400. The 63 and earlier had the Dynaflow, the 64 & later had the 400. A little research on prefixes willl give the years and compatibility. The old rule of modifications applies: "changing one thing changes two more." Iafraser, what is the car used for? What is your objective? A 401 in a Model A primarily used on the street is a pretty neat ride. If you mostly race it, that is a different deal.
401 + 425 intake interchangable Exhaust manifold 364-401-425 interchangable A good information site teambuick.com Good luck would love to have had a 425 in our special but found a good 401. Good Luck
there is also two starters up to 65 and mid 65 to 67. the turbo takes the 63-67 along with the flex-plate not that triangle looking thing.
I'm Running ST 400 tranny behind the engine. I have one of elesco's mini starters. Everything works fine. I will need to rebuild the 401 I have, but would prefer a 425 now that I see everything is interchangeable. The car is a street machine only.
Right now I'm running an Elerbrock 750 and its too much for the 401. I guesse 2 fours with progressive linkage would be OK. I'm really tight for space though as I run a full hood.
If you are going to go fast with your Nailhead, 401 is by far better. I have built a lot of Nailheads, 425's are great, but do have ring seal issues if you don't partially fill the block and once you go .040 on the bore, it's pretty much done short of a miracle block with extra iron in it. 401's are bulletproof and all the power in a Nailhead is in the heads/valvetrain. Your Edelbrock 750 should be just fine, but did you port the intake to match? You cannot just throw a 750cfm on a stock intake and go, the stock venture holes in the intake are sized for a 625cfm and that may be your issue. Also, the stock 64-66 single 4brl distributors are limiting once you go bigger on the carb. They can be recurved to a dual quad timing curve and work great. Believe it or not, a stock 401/425 actually likes an Edelbrock 800cfm carb once the distributor is recurved and the intake ported. Cam and heads like it even more! DQD
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