1967 gs400, 455 or 400??

[mr sunset]

I have a 67 gs400 and the previous owner installed a 1971 455wildcat engine. I see others doing this same transplant but why?
I would like to put the 400 back in. Is this a bad move?
Any information on this would be helpful. Thanks

[Dr. Frankenbuick]

The 400 was made in limited production (about 35,000) only for some (not all) Gran Sport Skylark for three years (67-69). The 455 was the only big block from 1970-1976, and it was in all of the big cars in addition those in GS Skylark. The aftermarket favored the more prevent motor with better parts options. There is not even an off the shelf forged piston for the 400. I think that is why most slip a 455 in place of the 400. It is just easier and cheaper to build. It also has some performance advantages by virtue of size alone.

[mr sunset]

Thank you, that explains the 400/455 conversions

what about the bolt ons, PS pump, ac compressor, exhaust manifolds ect. the engine I have has ex. manifolds on it but I don know if there 400 or 455. the rest of the exhaust is missing. I also bought a Rochester

1971 800 CFM Buick 455 QuadraJet # 7041540 Gran Sport GS, my engine didn't have one. 1971 800 CFM Buick 455 QuadraJet # 7041540 Gran Sport GS don't want to make expensive mistakes by not asking

This is my first buick project I'm not sure about a lot of the years and conversions that cross.
My thought is, If I put another 67 400bbb in I can hunt parts that were for that car. and they will fit.

Please advise

[Dr. Frankenbuick]

The 400/430 and 455 were basically the same engine with a different bore. They are externally the same, but you can not bore one to the next size as the internal castings are different (thinner). It my be that the accessories on your car were from the 400 to begin with and were bolted to the 455. Some parts were specific to the Skylark Gran Sport for hood and engine bay clearance and some were common on all 400/430/455s.

The exhaust manifolds were all basically the same except for 67. They have different casting numbers, but all are the same shape and design except for 67. All will fit in your car. Check our reference section for the casting numbers on yours.

Carbs had subtle differences in jetting and size year to year. I think the placement of the inlet is also different depending on year. There is a guy here that rebuilds Q-Jets and is aware of the differences year to year (Carmantx).

[mr sunset]

The 400/430 and 455 were basically the same engine with a different bore. They are externally the same, but you can not bore one to the next size as the internal castings are different (thinner). It my be that the accessories on your car were from the 400 to begin with and were bolted to the 455. Some parts were specific to the Skylark Gran Sport for hood and engine bay clearance and some were common on all 400/430/455s.

The exhaust manifolds were all basically the same except for 67. They have different casting numbers, but all are the same shape and design except for 67. All will fit in your car. Check our reference section for the casting numbers on yours.

Carbs had subtle differences in jetting and size year to year. I think the placement of the inlet is also different depending on year. There is a guy here that rebuilds Q-Jets and is aware of the differences year to year (Carmantx).

Thank you Dr. Frankenbuick.