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Block Basics – Section 2

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Section 02 -

Block Basics

2.0 Small Block

Generation 1 Cast Iron Small Block V-8 Facts

General. In 1964 Olds replaced their small block 215 V8 with a cast iron block of completely new design. The 330 V-8 shared none of its engine block architecture with that of the 215 V-8 and the 225 V-6 sourced from Buick. The engine was no longer aluminum, but cast iron, as weight became less of a factor with the engine going into both the larger mid-sized F-85s, Cutlasses and the full-size Jetstars introduced in that year. The engine was designed as a replacement for the 215, but was cast iron and enlarged in anticipation of the growth in size of the mid-size cars, where it was to be primarily used and as the workhorse for the entry-level full sized vehicles. Horsepower and torque for the 330 allowed for the engine to be installed in the full-sized Jetstars as the base engine and in 4-barrel form as the upscale powerplant. In 1968 the engine was enlarged to 350 cubic inches and used in 2-barrel and 4-barrel form.

This engine was offered from 1964 through 1975, when it was replaced by the Generation 2 small block. This engine was offered in five flavors with displacements from 260 to 403 cubic inches. (See below).

Not So Thin Wall Casting. The 330/350 small block was designed to be a “thin wall’ cast design, but because casting cores did not have the technology we do today, Olds built a little extra in the walls of the early blocks. Thus, blocks from 1964 to 1977 can easily be bored to 0.060”. All 330s can come out to the equivalent to a 0.060” over 350 which, for the 330 is 0.1815” over. We have seen 330/350s taken out to be able to take a 425 piston (4.125”), but the block should be sonic tested first. Frankly, the largest all this boring is going to do is take your small block to 360 cubic inches, a big gain in a 330, but only 10 cu. in. in a 350. If you are looking for more cubes – go to the big block. In our opinion, except for the 330, over boring should only be used to clean up the bores.

330 & 350 Block Key Differences. The key differences between the 330 and 350 are the 350’s larger bore and the 330’s forged crank.

1964 – 1966 Valve Lifter Angle. All 1964–1966 blocks used a different valve lifter angle of attack on the cam (45). Thus 1964–1966 330 blocks CANNOT USE 1967 AND LATER CAMS. All 1964–1966 cams WILL NOT WORK in 1967 and later blocks. Later blocks used a 39 lifter angle. Blocks with a “1” or “1A” cast up near the oil filler tube used the 45 lifter angle and should be avoided, if possible.

Early 330 Rocker Arms. The first run of 330 blocks was equipped with rocker arms similar to the previous 394 block that traces its heritage back to 1949. These rockers had a shaft that ran the entire length of the head to which the rockers were attached, similar to the Aluminum 215 and Buick engines. This is a very stable setup, but it weighs more and was more expensive to manufacture than the stamped steel rockers that are common on a 1965-1989 Olds. 1964 engines up to the engine serial number 034275 have these heads and should be avoided where possible.

Bore/Stroke. The small block does have the advantage of an excellent bore/stroke ratio and nice, easy to oil, main bearing sizes. As such it will rev to 6500 without spinning bearings if proper oiling is used. It makes more than enough torque for "A", "X" and "G" body performance.

Bearing Diameter. The small block uses bearing sizes similar to small block Chevys and thus has less bearing surface to oil, important as the engine rpms rise. The connecting rod journal size is 2.125”; the main journal size is 2.5000”.

Crankshaft. The 330 used a forged crankshaft and all others did not. The forged crank will take more abuse, however the cast nodular iron crank in the early 350 seems to hold up well in performance work. Significant in the forged versus cast crank is that the 330 uses a different flywheel bolt pattern than the 350. Thus, 330 flywheels and flexplates are only available in junkyards or from suppliers like Mondello and ATI. If you are scrounging a 330 block for the crank, take the flexplate too. (See the enclosed chart for the appropriate parts numbers).

Pistons. Pistons in all 260 through 403 engines (except the diesel) are cast, and use the same construction. As such, they have the same pin position/size, with only the piston bore as different. This allows overbored 330s to accept stock or aftermarket 350 pistons. However, the 330-350 blocks cannot be overbored to accept Generation 2 403 pistons, since the 403 block is siamesed. 350 diesel pistons are of a different construction and pin size.

Shared Components with the Big Block. The small block engine shared many of the components of the 400/425 big block that would be introduced a year later. This included the camshaft, rocker arms and springs, the cam bearings, the distributor, the starter, oil pan and front cover and water

The famous “Ram Rod 350” – the 1968 W-31 package. The air scoops fit under the bumper. It was also offered in 1969.

(This system was used on the 400 W-30 and W-32 as well).


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pump. The cylinder heads will bolt on, but they contain much larger ports and valves, and in most cases, these components hurt low-end performance (see W-31 engine option, below). With machining, the cranks could be interchanged as they are the same length, (the 330/350 utilizes 2.12" rod journals versus 2.50"; and 2.50" mains versus 3.00"), but there is little reason to do so as it is far more appropriate to select the block for the engine size desired. A 403 with the 3.975" 455 crank would be 480 cu. in. with a 0.030" overbore, however. Interesting.

Generation 2 Cast Iron Small Block V-8 Facts

General. This engine though so similar to the previous original 330-350 in size and block design, is considered a Generation 3 engine because of its "windowed" main bearing webs. This change is found in all the 260, 307 and 403 designs and the 350s constructed after 1976. All small blocks after 1976, including the diesel, used ½" head bolts rather than 7/16".

Thin Wall Casting. This block is truly thin wall cast, and weighs as much as 25 lbs less than 1964-1976 engines. None of these blocks should be overbored more than 0.030".

Windowed Mains. From 1977 onward all small blocks, including the 403 were produced with “windows” in the main bearing journal area, which obviously affects strength and longevity under hard use. (Diesel blocks are an exception). For 403 owners, there are rumors of solid main journal 403's, cast using the pre-1977 technique. Supposedly 2500 solid main 403's were produced in 1977 - used in the large Buick and Olds wagons. A solid main journal 403 can be determined by looking at the block casting number. 403 Block Casting Numbers: 557265-4A, 553990-4A, and 554990-4A are supposed to have no “windows”. With only 2500 produced, these are a rare but beneficial find.

Generation 2 Cast Iron Diesel 260 and 350 Block Facts

Diesel blocks. The diesel can be identified by a large “DX” cast right above the right hand center freeze plug and "D2" (260) and “D3” (350) by the oil fill tube. Diesel blocks are quite hefty, with 0.75” wide main bearing webs, 455 main bearing journal sizes (which have a diameter of 3.0003” rather than 2.4985”); hence they run 455 main bearing caps. They also have extra heft on all stressed areas, including the cylinder walls and the block deck. This block can be bored to 4.125” easily. Know that Olds big blocks and diesels send too much oil to the lifters, so if you intend to use this block (good for supercharged, road race, and nitrous applications), see Section 3.

Small Block Key Differences

Modifications to these engines will be covered in later sections.

Block. There are some significant differences between the small block engines. All 330 through 403 blocks use the same 9.330" deck height.

The 260: The 260 was designed and built to provide engines for Olds A and G body vehicles without relying on other GM divisions for a small, fuel efficient engine

supply and so as to use existing tooling. (Olds was the largest selling GM brand at the time). It was superseded by the 307 in 1982. Its small 3.495" bore, but standard small block 3.385" stroke kept it over square, but severely restricted the intake valve size and resulted in poor combustion chamber swirl12. Contrary to expectations, it was a very inefficient engine at a time when fuel efficiency was paramount. The 260 did not come with a 4 bbl manifold. 307 heads and intakes can be fitted, but the bores will have to be notched on the intake side.

The 307: The 307 was the last Olds V8. It was actually quite a good engine, and with the right parts can make excellent HP. It is a true 5.0 Liter engine, with a bore of 3.800" and the 3.385" stroke. Its "windowed" main journals are its weak point. If you are looking for big horsepower from a small block, utilize a 330-350. 330 and 350 heads can be fitted, but the cylinder bores will likely need to be notched for intake valve clearance, especially if the W-31 style 2.00" (or larger) valves are installed.

The 330: The 330 was the first "thin wall" cast Olds block. It came in two flavors: an early 45 lifter angle block and a 39 lifter angle block which was common to all later Olds engines. The 45 lifter angle block requires special camshafts and is not recommended, though if you are restoring a 1964-1966 Cutlass, cams are available for this engine. (The original 1964 442 did utilize this block).

The 330 followed the Aluminum 215's "under square" practice, with a bore larger than stroke at 3.9385" x 3.385". The 330 and 350 share many common pieces, except for the crank, which is forged in the 330. This requires a different flywheel/flexplate. The 1964-1966 330 also used an intake, in 4 bbl mode that was machined for a Rochester 4GC carb rather than a Quadrajet. The later 350 Quadrajet manifold will fit. 330s will take a 0.060" overbore safely and can usually be bored to accept 0.060" over 350 pistons (for a total 0.120-0.125" overbore) if desired. It is safer to stick to a 0.060" overbore, however to allow fitment of 350 pistons, however.

The 350: The 350 is a bored version of the 330 and as such, is greatly "over square" (4.057" x 3.385"). The 350 has the same deck height as the 300 and all other small blocks. It shares many common pieces with the 330, except for the crankshaft and pistons.

350's have been over bored to accept 425 pistons (0.098" for a total bore of 4.155") but for 16 cubic inches of displacement, the only reason might be to meet a maximum engine size of 6 liters for certain racing venues.

The 350 Diesel: For extreme use, the diesel block is the best bet. It is cast with more deck material and has much more sturdy main journal webs. In some areas, it is not

12 All Olds heads use the same valve stem center-to-center distance

of 1.910". This limits the overall combined size of the two valves, but also places the valves too far apart in the smaller bore engines. See the chart in Section 3 to see the impact of this circumstance.


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as good as the standard 330-350 because it is cut for the big block main journal size at 3.000", which means it has its own unique cast crankshaft. (A forged piece was offered from Moldex and may still be available). The larger mains mean that it does require more oil to lubricate these bearings, a good thing in a slow turning diesel, but somewhat of a detriment in a high revving small block.

The diesel can be overbored to as much as 0.185" and stroked to the 425's 3.975" stroke. If you are considering building a 350 diesel block, contact Mondello at www.mondellotwister.com.

The 403: The 403 has the largest bore size of any Olds engine at 4.351"and the small block's standard stroke of 3.385", and it used the same crank/rod combination of the 330/350. Unfortunately, it is a true thin wall cast block and contains the "windows" found in the 260, 307 and late 350. A main/crank girdle will help and can be sourced from the aftermarket.

Consider this block unique because of its siamesed bores, but you may swap intake manifolds, cranks, heads (the 403 uses a 455 intake and 350 exhaust valve and a big block sized combustion chamber), and cams from the earlier small blocks to wake the motor up. Do keep the revs under 6200 (it will rev way past that) to preclude main journal flex and crank walk, a deadly combo.

Cam, Heads and Valve Train. Heads, rocker arms, cam, lifters and valve springs will interchange between the all the small blocks, except for the early 1964 heads.

Heads: There are more different heads than any other element except camshafts in the small block engine. There were 17 different head castings during its entire run in both generation 1 and 2. 1968-1970 W-31 engines featured the largest overall valve sizes with a 2.00" intake valves and 1.625" exhausts with standard valves being 1.875" and 1.562" respectively for all 330 and 350 engines until 1977, when the intake was reduced to 1.500". The 403 ran 2.00" and 1.500". See the Head Casting Number Chart for detailed information.

All heads prior to 1971 (casting code "1" – "6" have the same port configuration and runners, even if fitted with larger valves. W-31 heads "5" &"6" have exactly the same ports and only have larger valves fitted. Use the common "5" and "6" series and merely fit the larger valves, if desired. If you desire stainless valve seats, consider the 1971-1972 "7" head. 1973-1976 "8" heads ran the big block 1.625" exhaust, but used a larger combustion chamber.

260 valves used 1.500" intakes and 1.300" exhausts. 307 valves were 1.750" for the intake and 1.500" for the exhaust. 403 valves were 1.995" intakes and 1.500" exhausts. As stated, the 260 can only run 307 heads as a performance upgrade, but the 307 can run 330-350 heads if the valves remain at non W-31 size. 403s can insert 455 exhaust valves, but should run their 4A head, due to port and combustion chamber sizing. (See the cylinder head chart in this Section).

Camshafts: There are quite a few selections for the small block, which hit the high water mark with the W-31. If you are building a modified engine, the aftermarket stocks quite a few cams for the engine. Almost all the stock spec cams are available from suppliers. Almost every stock spec cam is available from NROS suppliers. Supercars Unlimited can supply replacement cams for your application. www.supercarsunlimited.com. The 1985-1988 442 roller lifter cam and spring set is still available from GM. www.gmpartsdirect.com. (See the chart in this Section for a listing of cams).

Valve Train: 1964 Type "1" heads used different rocker arms and pushrods which are 8.235” long. 1964-1965 Type 1A and 2 heads (442 and B04 Police) used pushrods that are 8.3125” long, because of their rocker/pedestal setup that was used in that head only. "1" series heads have a different angle of attack for the pushrod hole because of the 45 lifter angle of attack on the early blocks. Thus, these heads would have to have the pushrod holes bored out to 0.562" to make sure the pushrods do not bind in the hole when mounted on 1966 and later blocks (engine casting codes "2" or higher).

1964-67 Type 3 Heads used pushrods are 8.400” long, and used the typical stamped steel rockers and aluminum pedestals. Starting in 1968 all small blocks used 8.2656” length pushrods. In 1986 the 307 changed to roller lifter cams with a much longer lifter requiring 7.718” length pushrods. 307 and 350 Diesel blocks that used the 0.921" diameter roller lifter that is longer which calls for the 7.718" length pushrod.

The 403 (left) and 307 (right) blocks - showing windows in main saddles. Note the lack of "meat" in the journal area. 307 actually has more!

The diesel block - showing sizeable main saddles.


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All standard small blocks used valve springs with 200-214 lbs. open pressure at 1.270" and 84 lbs at 1.670" at closed height. All W-31 engines utilized springs with 308 lbs. open pressure @ 1.270" and 108 lbs. closed pressure @ 1.670".

Starting in 1970, Oldsmobile fitted valve rotators on the keepers which increased the thickness and weight. These should be removed for high performance work because they do limit rpms. If removed, the valve spring seat requires shimming as the heads spring seats were cut deeper to compensate for the total spring assembly height difference. Thus, 1970 and later heads should be checked for these deeper valve seats and shimmed as necessary to retain the proper total valve height closed.

Crankshaft and Rods. The crankshafts are varied in specification from engine to engine, but will interchange, as all share the same rod journal size. The 330 crank is forged while the 260, 307 350 and 403 cranks are cast. All (except the diesel) use a 2.500" main journal. The 330's forged crankshaft can be successfully installed in the other small blocks with no increase in engine size, but an increase in durability, though few cast cranks will fail if properly checked and prepared.

The diesel crankshaft utilizes the big block's main journals, so it is unique to this block. There have been instances where inserts have been fitted to the diesel block so as to allow the use of the 330 forged crank or the 350 cast unit, so as to reduce the amount of oiling surface on the main bearings for high rpm work.

All Olds rods are forged, with the journal fillets being different on those utilizing the forged crank. (Best to collect the crank and the rods when switching over to a forged piece. 403 rods are larger and stronger and can be used in other small blocks if rebalanced, but must be modified to fit

forged cranks (an inexpensive fix). The same goes for the 350 diesel rod. Aftermarket 350 rods will work in the 260, 307, and 403, as well as with the 330 forged crank, if modified.

Intake Manifolds. The deck heights and heads for the 260 through the 403 means that all of the small block manifolds will interchange. The W-31 aluminum 4 barrel is a good swap for the 330, standard 350 and the 403 engine; and will fit the 307 and 260, but it is a bit pricey. Aftermarket manifolds for the 330-403 will bolt to the 307 and 260, but for the 260, a stock 307 4 bbl aluminum manifold is best due to the small ports and valves.

There are some excellent aftermarket manifolds for the small block. The Edelbrock Performer is a good all around compromise. This manifold is overkill on the 260 and it is recommended that the 307 4 bbl be used if switching over to a bigger carb.

All early stock 4GC carb manifolds can have their carb air entry holes bored out to take advantage of larger 4 GC units - or an adapter plate can be fitted. All early 330 engines can run later Quadrajet manifolds – preferably the 1968-1971 units, though the rare 1967 Quadrajet manifold is a bold on fit. If EGR is required, then utilize a 1973-1974 unit.

Pistons and Pins. 330 and the 350 pistons can be interchanged, if the 330 block is bored, with the 1968-1970 W-31 pistons delivering the highest compression, as they are flat-topped. Aftermarket 350 pistons up to 0.060" over can usually be installed in a 330. With the largest stock bore, but with the same deck height as the 330/350, the 403 is its own animal. Cast replacement pistons are available for all blocks except the 330 from Sealed Power and others. Forged aftermarket pistons are available for the 307, 330, 350 and 403, but not for the 260.

2.1 Big Block

Generation 2 Big Block Facts

The 400-455 "big block" is really the second generation modern Olds V8, with the Generation 1 engine being the "Rocket" introduced in 1949 and used through 1964. It is covered in a separate manual. The 1965-1976 big block will be called the "Gen 2 Big Block" to differentiate between the original Rocket V8. The concept of the big block, as introduced in 1965, was to recast the new small block with a higher deck to allow a longer stroke.

Obviously, certain changes were made to accommodate the higher loads that would be faced. Thus, though the block is considered a "thin wall" design, it is really not, although design factors did allow it to be about 50 lbs lighter than the Gen 1 engine.

1965-1967 Blocks versus Later Engines – There was a major change made to the big block in 1968 - a stroke change from 3.975" to 4.250". On the mid sized car's engine, the longer 4.250" stroke was adapted, but the bore was reduced to 3.870" to meet the GM mandated 400 cubic inch limit. The crankshaft was metallurgy was changed from forged steel to cast nodular iron. The 400 and 455 also had the block notched when cast to allow the rods on the longer stroke crank to clear block bores.

Thus the key differences are the late block’s new crankshaft with a larger stroke of 0.275” for a total of 4.250” compared to the earlier block’s forged crank, with its stroke of 3.975”.

The experimental W-43 four-valve “Hemi” of 1971 which supposedly delivered 550 HP in emissions legal street trim!


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1964 – 1966 Valve Lifter Angle. All 1964–1966 blocks used a different lifter angle of attack on the cam (45 and some with a 0.921” lifter diameter rather than 0.842"). Thus 1964–1966 engines CANNOT USE 1967 AND LATER CAMS. And all 1964 – 1966 cams WILL NOT WORK in 1967 and later engines. Later engines used a 39 lifter angle, with 0.842” lifter diameter, except all 1966-1967 400 blocks and all Toronado and some Starfire 425s in the same years.

As stated, all 1966–1967 400s use the later lifter angle, and have the larger diameter (0.921”) lifter bores. Check the block before ordering the cam. Blocks with an “A” and “B” and with a "D" and with no drill spot cast up near the oil filler tube should be avoided as they have the old 45 lifter angle and few NROS cams are available.

1965 Rocker Arms. The 1965 engine used an interim rocker arm assembly and pushrod length that is slightly different from the setup common to all later Olds V8s. Thus, "A" casting code heads should also be avoided due to this circumstance, as these components may be unavailable from parts suppliers. "A" heads can be converted to the later setup.

Bore and Stroke. As mentioned earlier, the 1965 – 1967 engines utilize a stroke of 3.975" coupled with a forged crank to make their displacement. Unless you are looking for killer cubes, this engine is a better choice for high rpm power production.

Bearing Diameter. The one critical difference in the big block is the main bearing journal size, which is 3.00” versus the small block’s 2.500”. Connecting rod journals are also different, with the big block at 2.500” and the small block at 2.125”. The bigger journals handle load better, but can have oiling issues as the RPM increases.

Crankshaft. The early 1965-1967 engines used a forged crankshaft. Because of balance issues, there is a significant difference in the forged cranks that the 400/425 used – The early cranks had a different flywheel bolt pattern than the 400 long stroke and 455. The forged crank flywheels and flexplates are only available in junkyards or from suppliers like Dick Miller.

When you are scrounging that 400/425 block for the crank, take the flexplate as well. (We have included the factory parts numbers for the forged items on the Block ID page). There is a section on visual ID on a later page.

You will note that using a 1965–1967 400 cubic inch block with a late 455 crank will yield a 7 liter stroker, while using the early crank in a 1968 -1969 400 cubic inch block will yield a 6.1 liter big block. If you need to sit inside a certain cubic inch limit and want TORQUE, the 374 might be for you. If you are looking for 425-427 cubes, stick with the early 425, its shorter stroke is a better bet.

We do suggest using a 1968-1972 455 “F” casting block with the 1965-1967 425 3.975” crank if you are building a 425, as you won’t have to worry about valve lifter angle. It should also be noted that the late 400 and 455 blocks are notched to accept the 4.250” crank throw. If you wanted to upgrade a 425 to a 455, you would need to replicate those notches in any 1965-1967 block.

Pistons. Pistons in all big block engines are cast and use the same construction. As such, they have the same pin position/size, with only the piston bore as different. This allows the early 400, which can be overbored to 4.125" accept 425 pistons. However, while the 400 long stroke could use a 455 piston, these blocks do not seem to be able to accept the 4.125" overbore. Surprisingly, the old 400 short stroke can use the 350 piston, if overbored 0.060".

Shared Components with the Small Block. The big block engine shared many of the components of the 330 block that was introduced a year earlier. This included the camshaft, rockers, & springs, the cam bearings, the distributor, the starter, oil pan and front cover and water pump. The cylinder heads will bolt on, but they contain much smaller ports and valves, and in most cases, these components would hurt performance. With inserts, the mall block cranks could be interchanged as they are the same length, (the 330/350 utilizes 2.12" rod journals versus 2.50"; and 2.50" mains versus 3.00"), but there is little reason to do so as the best result would be a 373 cubic inch big block (3.975" crank), since the 4.250" crank throws will hit the cam. (Olds did build a 373 engine for testing purposes). It is far more appropriate to select the block for the engine size desired.

Generation 2 Big Block Key Differences

Block. There some significant differences in each block, however all Generation 2 Big Blocks us the same 10.625" deck height.

The Early 400. The 400 was designed to meet the GM-mandated 400 cubic inch limitation for Intermediate cars. This was accomplished by reducing the bore of the big car's 425 by 0.125" to an even 4.00" and retaining the 425's 3.975" stroke. Other than this, the 1965 400 blocks were identical and merely used this bore and stroke combo. All components used on the 425 will interchange. These blocks are casting code "B",

The 1966-1967 400s were Toronado 425 clocks utilizing its 39 lifter angle and 0.921" large circumference lifters that were again under-bored to 400 cu. in.

The Early 425. The first 425 was a beautiful casting, with hardly any flash and with good tolerances, however it used the older 45 lifter attack angle and should be avoided as few factory or aftermarket cams are available,

1965 rocker arm setup, note Chevy style studs but unique pivots and retainers. The 1966-1989 system was less expensive to build. This earlier

system did allow easier lifter pre-load setting.


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though Isky and Engle will grind cams for this block. This block is coded "A". In most cases, you are just better off, cost wise, utilizing the 1966-67 425.

The Late 400. This may be the best of the lot, if you are looking for a 400 cu. in. engine. In fact, there were many racers who reverted to the 1967 400 in 1968 when their long stroke 400 dumped. The casting tolerances are better in this block and it has the modern 39 lifter attack angle, however, because of this, it may not be possible to bore this block 0.125" over to make a 425. Sonic test the block before attempting this overbore. 1966-1967 400s 50 425 specs. These blocks are coded "E".

The late 425. There are two late 425's, the passenger car 425 and the Toronado. Both will be coded "D", and have a "drill spot" next to the letter. Strangely, the Toronado engine blocks featured the same 0.921" diameter lifters as used on the 400, but the 88 and 98 425's did not, using the standard 0.842” diameter lifter in their blocks. These blocks can safely handle a 0.060" overbore, which will deliver 438 cu. in.

The Long Stroke 400. Offered for only two years, the long stroke 400 was delivered so as to make the mandated GM 400 cu. in. limitation for intermediate cars. This was accomplished by under-boring the now standard 455's 4.125" to 3.870". Unfortunately, Olds did not just take a 455 block and machine it to this lesser bore. The 400 block was cast with smaller cores, and as such can only be overbored 0.060" safely. Some early 1968 blocks have been bored to reach 4.000" (0.130"), and the early 400 piston could be fitted. The net engine size would be 428 cubic inches. All 400 long stroke blocks are coded "G".

The 455. Offered as the major big block engine from 1968 through 1976, the 455 powered almost 2 million vehicles. It was cast in four different series; Sans Serif "F" code (1968-1970), Serif "F" code (1971-1974, with clutch ball), "FA" code (1972-1975 w/o clutch ball), and "L" code (1976 w/o clutch ball), for motor homes and marine applications. All 400 long stroke and 455 blocks are cast with "notches" for connecting rod clearance due to the 4.250" stroke.

Cams, Heads and Valve Train. Heads, rocker arms, cam, lifters and valve springs will interchange between the all the big blocks, excepting the 1967 "A" heads. Valves are different sizes and ports are different from head to head and among different application, with the average intake at about 2.00" and the exhaust at 1.625".

Heads: There are more different heads than any other element except camshafts in the Gen 2 big block engine. The 400 and 425 had 3 different head castings during its run. 1967 400 W-30 engines also featured in 2.125" intake valves (standard was 2.000") and 1.630" exhausts (standard was 1.625"), which were carried over to all future W-30s. See the Head Casting Number Chart for detailed information.

All heads prior to 1968 (casting code "A" – "C" have the same port configuration and runners, even if fitted with larger valves. W-30 heads "D", "F", "FA, "H", "HA", "K", and "KA" have a raised floor and one of the heat riser passages blocked by the casting, and do flow better, but not appreciably. The H and K series heads utilize stainless valve seats. If you can find a set in your junk yard jaunts, get them, but otherwise, use the common "C" and "E" series and "G" and "GA" (stainless seats) series. Avoid the "J" head as it does have some restrictions. (See the chart in this Section).

"A" series heads have a different angle of attack for the pushrod hole because of the 45 lifter angle of attack on the early blocks. Thus, these heads would have to have the pushrod holes bored out to 0.562" to make sure the pushrods do not bind in the hole when mounted on 1966 and later big blocks (engine casting codes "D" with drill spot, and "E" - "L").

Cam: There are quite a few selections for Gen 2 Big Block, which became more interesting when the W-30 and H/O were offered. See the cam chart in this Section for details on cam specs. If you are building a modified engine, the aftermarket stocks quite a few cams for these engines. Almost all the stock spec cams are available from suppliers.

Valve Train: Gen 2 big blocks initially adopted a valve train similar to the 1964 small block, with the 67-69 engines borrowing the rockers from the 1964 second stage small block, though they moved fairly quickly to similar rockers and pedestals that were used until the engine was discontinued in 1989.

Lifters came in two sizes on early big blocks; 0.842" and 0.921" diameter. The 0.921" lifter is 0.125" TALLER than the 0.842. Thus there are two pushrod lengths fitted in these early engines. All big blocks from 1968 on had 0.842" lifters.

1965 400-425 pushrods are 9.6250” inches long, due to using an interim rocker/pedestal type. 1966-67 engines using the 0.921 lifter had pushrods that are 9.4375” long, due to the usage of these longer lifters. (These engines used a different lifter that was 0.982" in diameter and 0.125" longer. Starting in 1968 all big blocks used 9.5781” length pushrods because they all used the 0.842" lifter.

Valves were standard at 2.00" intakes and 1.629" exhausts. Starting in 1968, W-30 valves were 2.100" on the intake side and 1.630" on the exhaust.

The 455 block above clearly shows the "notches" cast in the block to allow rod clearance.


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All standard 400-455s used valve springs with 214 lbs. open pressure at 1.270" and 84 lbs at 1.670" at closed height. 1965 High Performance (precursor to the W-30) engines ran dual springs with 315 lbs. open pressure and 115 lbs. closed. All W-30 cars, starting in 1966, utilized 308 lbs. open pressure springs @ 1.270" and 108 lbs. closed pressure @ 1.670".

Starting in 1970, Oldsmobile fitted valve rotators on the keepers which increased the thickness and weight. These should be removed for high performance work because they do limit rpms. If removed, the valve spring seat requires shimming as the heads spring seats were cut deeper to compensate for the total spring assembly height difference. Thus, 1970 and later heads should be checked for these deeper valve seats and shimmed as necessary to retain the proper total valve height closed.

Crankshaft and Rods – All 1965-1967 big blocks used a forged steel crankshaft with a 3.975" stroke. All 1968-1976 big blocks utilized a cast nodular iron crankshaft with a 4.250" stroke. All big blocks used 3.250" main journals and 2.500" rod journals. The connecting rods are almost indestructible forged steel with the 1965-1967 engine using a 6.986" center to center length and the 1968-1976 engine using 6.736" length pieces.

Intake Manifolds. The deck heights and heads for all the big block engines is the same, which means that all big block manifolds will interchange. The W-30 aluminum 4 barrel is a good swap for any mildly modified big engine, but it is a bit pricey. Aftermarket manifolds are all interchangeable and are best fitted based upon performance criteria. We will cover the best setups later on in this manual.

There are some excellent aftermarket manifolds for the big block. The Edelbrock Performer is a good all around compromise, and the Offenhauser tunnel port (pictured) should only be used in all out drag racing situations.

All early stock 4GC carb manifolds can have their carb air entry holes bored out to take advantage of larger 4 GC units - or an adapter plate can be fitted. All early 400-425 engines can run later Quadrajet manifolds – preferably the 1968-1971 units, though the rare 1967 Quadrajet manifold is a bold on fit for the early cars if the original hot air style choke is desired. If EGR is required, then utilize a 1973 - 1974 unit big block unit, though it is heavy and not too efficient.

Pistons and Pins. Early 400 and the 425 pistons can be interchanged, if the 400 block is bored 0.125. All early big block pistons delivering high compression at 10.25:1, with

the 400 utilizing a flat-topped piece. 350 W-31 forged units ( available from Sealed Power) can be fitted if the block is bored 0.060" over (412 cu. in.) as all Olds V8 engines from 1964 to 1988 use the same piston pin to piston top height.

If your 400 long stroke block is sonic tested and will support a 0.130" overbore, the W-31 piston can be fitted – for a 440 cu displacement – however, the compression will be 11.5:1. 330 and 350 low comp pistons can be fitted with the 330 slugs delivering a 415 displacement. In this case, the engine will have about a 9.50:1 compression ratio.

Aftermarket 455 pistons up to 0.060" over can be installed in a 425. Cast replacement pistons are available for all blocks except the 425 from Sealed Power and others. Forged aftermarket pistons are available for all units from suppliers such as Dick Miller www.dickmillerracing.com.

See the chart in this Section for typical piston/head/block possibilities.

Why Long Stroke (under square) Big Blocks were Developed. In the 60s and early 70s, the public was demanding larger cars with increased weight. To meet these requirements and to offer similar or greater performance, GM and others decided that larger, slower turning engines were the easiest way to meet theses demands. Manufacturers at that time also favored longer stroke engines because they delivered more torque at lower RPM, which made for a quieter and smoother engine (and helped meet the newly mandated emissions requirements).

Olds was forced to increase stroke because the center-to-center distance of the cylinder bores would not allow increases in bore sizes beyond 4.125” without siamesing the bores (as they later did with the 403). This limitation was the result of designing and manufacturing the block with the bore to bore centers of the small block, so they could be machined on the same assembly line.

But Olds learned in 1968 with the 400 cubic inch 442, this drastically (and sometimes calamitously) increased rod side loading on the rod bearings during high RPM and resulted in spun bearings. When the 442's with the 455 appeared in 1970 the problem was reduced, as the 455's 4.125" bore stabilized the piston and reduced rod side loading. The net/net was that the 455 was designed more as a slow turning luxury car engine, not as a performance true piece.

By utilizing the different bore and stoke combinations available, big blocks can end up with a few engine sizes beyond that of the factory offerings. The table below shows all possibilities.


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2.2 Crankshaft Identification

Crankshaft Identification – Forged Cranks

The following chart, with the diagrams and pictures will assist you in identification of Oldsmobile forged crankshafts.

For about the first month of production, the Olds 455 received a forged steel crankshaft (Casting number 400943). After the first month, only cast iron cranks were used.

Turn crank until you notice that the opposite two bolt holes do not line up across from one another. If you turn the crank until one of the holes that does not line up is to the right, the opposite hole will be ABOVE the centerline of the opposite hole.

Flexplate

ATI Transmissions www.atiperformanceproducts.com (part number 915563) and Mondello www.mondellotwister.com carry a SFI approved flexplate for the 330-425 engines Specify engine block.

The early (forged) crank flange - showing two holes that do not line up on the left and right.

Late 1964 - 1967 330 forged steel cranks have the number "388-776" on the last counter weight of the

crank by the rear main.


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Crankshaft Identification – Cast Cranks

The following chart, with the diagrams and pictures will assist you in identification of Oldsmobile cast crankshafts.

Turn crank until you notice that the opposite two bolt holes do not line up across from one another. If you turn the crank until one of the holes that does not line up is to the right, the opposite hole will be BELOW the centerline of the opposite hole.

Flexplate

ATI Transmissions www.atiperformanceproducts.com (part number 915565) and Mondello www.mondellotwister.com carry a SFI approved flexplate for the 330-425 engines Specify engine block.

The late (cast) crank flange - showing two holes that do not line up on the left and right.

1968 – 1972 455 nodular iron cranks will have the number "397363" on the last throw of the crank by the rear main. The crank will display a "NAK" or "N" as shown above.


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2.3 Factory Specifications V-8 Engines

Factory Specifications – Block Info

The following specifications are based upon published reports, factory brochures and service manuals, factory updates, and factory technical bulletins. Where ambiguity resulted, we have chosen what appears to be the most common specification. If you have information that is better than what is here, you may send it to the manual editors at [email protected].


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Factory Specifications – Head Info

The following specifications are based upon published reports, factory brochures and service manuals, factory updates, and factory technical bulletins. Where ambiguity resulted, we have chosen what appears to be the most common specification. If you have information that is better than what is here, you may send it to the manual editors at [email protected].


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Factory Specifications – Head Info Continued


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Factory Specifications – NOS Camshafts and Valve Springs

The following specifications are based upon published reports, factory brochures and service manuals, factory updates, and factory technical bulletins. Where ambiguity resulted, we have chosen what appears to be the most common specification. If you have information that id better than what is here, you may send it to the manual editors at [email protected].


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Factory Specifications – NOS Camshafts and Valve Springs Continued


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Factory Specifications - NROS Camshafts and Valve Springs

The following represent vendor(s) who have shown the ability to deliver quality parts meeting or exceeding OEM specifications. Other manufacturers may deliver equivalent parts; however we have no feedback or hands-on experience with their offerings.


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Factory Specifications - NROS Camshafts and Valve Springs Continued

Documents

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