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425 to 400 (B) interchangeabilty


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My 65 gs skylark restore project is becoming a nightmare! I had started to have a 425 (1966) rebuilt however ended up with a cracked block. I have the option to use a 400 B block (the casting # indicates a 400 ci 59-66 useage in buick)to install but I need to know if the parts are interchangeable.( Is the 400 b block a 401?)<BR>Physically they look the same, Is there any advantage to using the 425 heads,are valves larger or smaller on 66 heads? the 66 425 intake appears to be superior due to the bores are larger.<BR>Does anyone have info to assist me? Parts in Canada appear to be in very short supply so my options are limited.<BR>My goal is to make this gs perform as a daily driver and fun machine!

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One thing that you must watch when working with 401 buick engines is the back of the crank. The 63 and earlier engines had Dynaflow transmissions, and the 64 up engines had turbo 400s . The back of the crankshaft is machined to accept one or the other ,and they won't interchange. The 400 in the 65 was in reality a 401,but gm had a 400 inch limit in the A body cars, consequently the 401 conviently lost one cubic inch All the 425 Buicks were machined to accept the 400 turbo.

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Hey aren't you in on the wrong side of this site? You sould be over in the Buick club of America side. Or check out this Nailhead email group>>> <A HREF="http://groups.yahoo.com/group/BuickNailHead" TARGET=_blank>http://groups.yahoo.com/group/BuickNailHead</A> <<<<< join it and you will get all the info you could ever need. <BR>Oldguy is right on target on the rear of the crank issue. The heads are the same as far as I know, and Old guy not all 425s had a quadrajet, it was an option. <P>------------------<BR>buickfam@aol.com<BR>Life long Buick Fan.<BR>1965 Skylark H/T<BR>1965 Gran Sport Convertible<BR>1948 Chevy Pickup with 401 Buick.<BR>"Fan of anything that moves human beings"

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I had fun at the drags with a Gran sport.We had a Quadrajet and sneaked in a THM 400 We won the Gold Cup,beating out a factory sponsored Brand X with 8 bbls of carburetion.Those "Nail-Heads" will rsally run when they are set up correctly.I still have a 1965 THM 300 for sale(Fits 401 eng)

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