ENGINE HP CARB. TRANS. COMP. CODE
225 V6 155 2-BBL AT/MT 9.00:1 LH
225 V6 --- 2-BBL AT/MT 7.60:1 LJ(export)
330 V8 250 2-BBL MT 9.00:1 Ql
330 V8 250 2-BBL MT 9.00:1 QJ(HD clutch)
330 V8 --- 2-BBL MT 8.30:1 QK(export)
330 V8 250 2-BBL AT 9.00:1 QA
330 V8 250 2-BBL AT 9.00:1 QB(with A/C)
330 V8 --- 2-BBL AT 8.30:1 QC(export)
330 V8 315 4-BBL MT 10.25:1 QV
330 V8 315 4-BBL MT 10.25:1 QX(HD clutch)
330 V8 --- 4-BBL MT 8.30:1 QY(export)
330 V8 315 4-BBL AT 10.25:1 QN
330 V8 315 4-BBL AT 10.25:1 QP(with A/C)
330 V8 --- 4-BBL AT 8.30:1 QO(export)
400 V8 345 4-BBL MT 10.25:1 QW
400 V8 345 4-BBL AT 10.25:1 QR
Early 400
Built 1965 - 1967.
Late 400
Built 1968 - 1969.
The short stroke 1965-67 400s are awesome motors, but in 68-69 Olds attempted to reduce emissions by using a reduced bore to minimize combustion chamber quench area and thus lower unburned hydrocarbons (emissions controls actually started in 1968 on 49-state cars). Note that this decision to go with a smaller bore was also due in no small part to the desire to use a common crankshaft with the new 455 in 1968 as well. The result is a terribly undersquare motor (3.870 bore x 4.125 stroke) which won't rev very well. This is the worst bore-to-stroke ratio of any American V8 from the modern era.
One limiting factor to your buildup will be the small bore size of your later 400, which can shroud larger valves. One great way to gain yourself some horsepower is to move up to a 455 shortblock with your stock "C" heads; more cubic inches, and the large valves will breathe even better.
The story on the change from the early 400 to the 68-69 400 was due to design changes to start limiting emissions and with the longer stroke they picked up more torque which lead to more power at lower rpm. Thus their early attempt to reduce gas consumption and increase mileage with lower emission. Plus the redesign of the internals which now shared the same crank and rods as the 455's.
I recall reading that the undersquare design of the 400 and 455 in 1968 was intended to reduce the quench area in the combustion chamber to reduce emissions. Apparently, the walls of the combustion chamber are cooler than the rest (makes sense) and fuel can condense out there and lead to incomplete burning and thus higher HC and CO emissions. By making the bore smaller, the surface area of the combustion chamber is, by definition, reduced.
Of course, while that was the published rationale, I suspect that this decision had more to do with commonality of the expensive crank forging between the 400 and 455 than anything else. Since Olds likely expected to sell many more 455s than 400s, redesigning the 400 to use the 455 crank and rods probably made a lot of financial sense.
[ Thanks to Rob Thomas, Bob Barry, Joe Padavano for this information ]
Rev Potential, Limit
The early 400 engines rev higher than any other big block. They will rev higher than a 425. Got a little less piston mass. These things will turn almost 7000 RPM.
[ Thanks to Jim Chermack for this information ]
ID Code
