General Information
Note: The information contained in all
of the "Engine Detail" sections should be read before proceeding with
modifications, etc., because some information that applies to all engines, or
all small blocks or all big blocks, might not be duplicated in every section.
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 ]
Rebuilding
Cylinder Boring
The E block (early 400) can only be safely bored .100. That's all. The
cheapest way to go is get standard 350 pistons and bore the engine .057". They
work great. You can even get the flat top W-31 pistons and have it the same
as the originals. I've used these before with excellent results.
Although the 1965-1967 400 and 425 used the same crank and rods,
the blocks are different castings. The maximum overbore
recommended by Oldsmobile is .060. I've heard of guys using
the 425 pistons before, but if it were mine, I'd sure want to have
the cylinders sonic checked for thickness. Excessively thin
cylinder walls will lead to overheating due to less material to
dissipate the heat. Thin cylinder walls will also distort much
easier, resulting in poor ring seal.
You would want to at least
use torque plates when boring and honing the cylinders
(This should always be done on an Olds engine anyway).
If this is a (drag) race only engine, I would recommend you
use a water jacket filler available from Hard Blok, Moroso, etc.
However, if this is a driver, cruiser, etc., I would
rather sacrifice the few cubic inches gained than compromise
longevity.
Ran my question about the 425 piston into the 400 'E' block by 'the rocket
scientist', Chris Witt, and he related seeing a cutaway 400 engine at MSU. He
recalled being amazed at the thickness of the cylinder--he measured 3/8".
Sounds like going .063 won't pose any problem there. Apparently JM also says
it's an OK deal.
[ Thanks to Jim Chermack, Greg Rollin, Peter Sliskovich for this information ]
Buildup
Piston to Valve Interference
The Olds engine your thinking of is the 65-67 400's. They all
used flat top pistons and had the same A, B, C, heads that were used on
all engines during those years.
The 66-67 W-30's even used that .474 lift / 308 duration cam. So there
shouldn't be any piston to valve clearance problems. My Olds engine guru out here
says that piston to valve clearance comes into effect after about .560 lift
with alot of duration.
[ Thanks to Jim Chermack for this information ]
Buildup Examples
Tuning / Power Boost