Special thanks to Scott Martindale for submitting this article.

Olds Rocket V8s By Marlan Davis

For those of you who may not think "Oldsmobile" and "performance" are synonymous terms, Oldsmobile's performance heritage dates all the way back to 1903, when an Olds-built "Flyer" established the world's lightweight speed record of 54 mph. In conjunction with Cadillac, Olds later introduced the first modern overhead V8 engines in 1949. NASCAR's 160-mile Grand National stock car race at Daytona was won in 1953 by a Bill Blair-driven Olds at a new record average speed of 89.5 mph. Later in the decade, buyers of 1957 and 1958 Olds models could opt for a 371-inch, triple deuce "J-2 Rocket" rated at 300 hp. The early '60s saw the introduction of an all-aluminum 215 cubic-inch V8, some of which came with factory turbochargers.

In 1964 the first modern Olds V8 debuted as a 330-inch small-block. The 400 and 425 big-blocks followed in 1965. In 1966 the hot 4-4-2 L69 400 inch option came with 3x2 carburetion, fresh-air induction, and a hot hydraulic cam. Underrated at 360 hp (just 10 hp, more than a 4-barrel stocker), the option went for only $264.54!

GM's corporate edict soon eliminated multiple carbs, but Olds wasn't through yet. In January 1968 the 325-hp/350 inch W31 Ram Rod Cutlass option produced a conservative 325 hp. Meanwhile, the giant 455-inch motor was waiting in the wings, first appearing in full-size passenger cars and Toronados, then in Hurst-Olds specialty cars, and finally in the legendary W30 4-4-2 intermediates.

Big Brother put a stop to the horsepower wars starting in 71, with the big-block finally dying out for good after 1976. The 350 soldiered on, being joined by the 403 in 1976. Both were superseded in 1980 by the 307. Olds converted the 350 into a diesel engine from our point of view, the best that can be said for it is that the beefy diesel blocks provide a strong foundation for an all-out racing gasoline small-block

Among knowledgeable engine builders there's an old (Olds?) saying: "Horsepower sells engines, but torque wins races." It's also a fact that the loads on an engine's reciprocating parts increase geometrically with each incremental rpm increase. With this in mind, it stands to reason that the plan for consistent engine power and longevity on the street is ample low and mid-range torque; not excessively high rpm. With many of the "most popular" engines, this approach isn't possible, since they seem to really work well only with high compression ratios and high rpm. But it is possible to make mountains of torque without spending mountains of dollars by using a commonly overlooked engine-the Oldsmobile V8. Available in both small-block and big-block versions with displacements ranging from 260 to 455 cubic inches, Olds engines abound in junkyards all across the nation.

Modern Olds V8 engines displacing 260, 307, 330, 350, and 403 inches are considered to be small-blocks. Big-blocks displace 400, 425, or 455 cubic inches. The small-block motors are 1-inch shorter in height and 1-1/2 inches narrower than the big-blocks. If the engine's original factory paint is still intact a small-block will be gold or blue, while the big-blocks can be red, green, blue or bronze. Late-model 307's are flat black. You can also identify engines by casting letters and numbers.

While exceptions will be noted below, as a general rule the following parts are physically interchangeable among all "modern" Olds V8 engines: flexplate and flywheel, engine mounts, oil pan, front cover, water pump, bellhousing (also interchanges with modern Buick,and Pontiac), oil pump, oil pump driveshaft, rocker arms and fulcrum (except early 330), camshaft and lifters (except for different lifter bank angles and lifter diameters; see below), harmonic balancer, cam bearings, timing chains and timing gears. Heads will basically interchange, except manifold ports may not align.

Before taking a closer look at small and big-block specifics, we will examine several weaknesses common to all Olds engines: oil system, bottom-end strength, and valvetrain.

In stock form, the production oil system can't do the job above 5000 rpm. To begin with, you'll suck the oil pan dry. The old '66-'78 Toronado pan (part No. 398438) will hold an extra quart (six with filter), compared to other stock pans. Naturally, an extended oil pump pickup is required with deepened pans, preferably a fabricated tube of at least 5/8-inch diameter. Increased oil pressure is also required; it can be achieved by installing a stiffer relief spring, or ultimately, via the installation of a special aftermarket high-volume oil pump. On serious engines, oil restrictor kits are used to limit the amount of oil reaching the top end, retaining the vital lube downstairs where it's needed to keep the main and rod bearings alive.

Also needed on an all-out high-rpm engine are main studs and better rod bolts. Four-bolt caps may be added to diesel and big-block engines. On this type of engine, special ultra-lightweight pistons and rods are used to reduce strain on the bottom end.

While the above problems only become critical on race motors, valvetrain deficiencies manifest themselves practically every time a cam is changed, the block and heads are milled, or a simple valve job is performed. In stock form, the Olds valvetrain is non-adjustable, so no tolerance exists for changes anywhere in the system. For example, since the common everyday valve job moves the valve seat higher up into the pocket, the valve stem height is effectively increased, often upsetting the valvetrain geometry (knowledgeable Olds head shops can compensate by slightly reducing valve stem length). To permanently correct these problems, there are several solutions. They are (from cheapest to most expensive): shimming or milling the rocker arm pedestals, installing adjustable pushrods, or converting to adjustable rocker arms by the use of a bolt-on aftermarket kit. The latter solution is really the most practical.

There are also valvetrain component interchange problems you should be aware of. Early engines used both 39-degree and 45-degree lifter bank angles (see chart), as well as two different tappet diameters. When ordering an aftermarket cam you must specify which engine you have. The 1964-'65 330/400's also used a different rocker arm design, for which parts these days are extremely hard to come by. Except for these early motors, rocker arms and fulcrums will interchange on all engines through 1979. Pushrod length is the same for all small-blocks. Big-block pushrods are longer, and may vary between different displacement motors by as much as .042-inch (although aftermarket sources say they'll effectively interchange). In 1980 pushrod tip diameters were increased from 5/16-inch to 3/8-inch, with corresponding changes made to the rocker arms and lifters. The two different diameter pushrod designs must be used with the correct corresponding rockers and lifters. Both systems interchange as assemblies. Since aftermarket lifters are designed for 5/16-inch pushrods, you must either use early pushrods and rockers or a special Mondello pushrod that has dissimilar ends (one 5/16 and one 3/8). Finally, the '81-up diesel (block stamped "350-DX") and '85-up 307's use hydraulic roller camshafts, with a .921-inch tappet diameter. The roller lifter design is too heavy for high-rpm performance use. However, you could use an early .921-inch diameter hydraulic tappet mated to a conventional hydraulic cam ground for a 39 degree lifter bank angle.

Forged cranks are distinguished by wide forging mark compared to narrow casting seam. Big block forgings have forging No. located on rear throw while cast cranks have No. on second throw from front. The 425 forging has no hole on No.1 throw unlike 455 cranks.

All small-blocks feature a 3.385-inch stroke, with displacement varied by increasing the bore diameter. Main and rod journal diameters are all the same, except for the 350 diesel which uses 455-type mains with standard small-block rod journals. All gas small-block cranks are completely interchangeable, except for any rebalancing required when changing pistons and rods. The 1964-67 330 engines were the only small-blocks to use a forged steel crank; it is preferred for all-out, 7000 plus-rpm competition. These early 330 forged cranks (as well as some big-block cranks) have slightly different flywheel bolt patterns, requiring a unique flywheel or flexplate that's currently available new only from Dave Smith Oldsmobile and Mondello Performance.

For application under 7000 rpm, the '68-'70 nodular iron 350 crank is adequate. Since many '71-up 350 cranks and most 260, 307, and 403 cranks are only cast iron, and also have cut-down counterweights, they should never be revved beyond 5500 to 6000 rpm. Non-forged crank longevity can be improved by reducing piston and rod weight.

The diesel blocks are preferred for all-out racing because of their 3/8-inch thick main webs and .400-inch-thick cylinder walls. A 425 crank with cut-down counterweights will fit in the diesel block. Since, with sonic testing, the diesel block will accept a 4.25-inch bore, up to 451 inches is available with custom pistons and rods (what a sleeper!) 455 cranks won't clear no matter what you do).

Even without a sonic test, diesel blocks can easily be bored 1/8-inch over which still leaves greater wall thickness than a late-model casting, which can safely be bored only .030-over. These late thin-wall gas blocks were produced in 1976 and later, and may be identified by their weak "windowed" main webs. The 403's have relatively thick siamesed cylinder walls, but most have the late weak main webs. "Normal" '68-'76 gas 350's will go 1/8 over after sonic testing, yielding about 370 cubic inches. The 330 blocks will also accept 1/8-inch overbores. The '68-70 350's (cast "558") or early 330 blocks (cast "917") are preferred due to their higher nickel content.

All small-block rods interchange, except for the slightly shorter diesel rods. All are forged, except for some late 260/307 pieces. The best rod (part No. 555142) is found in 403 engines; made from a better alloy, it is also 10-percent larger across the beam.

When it comes to pistons, all factory slugs are cast flat-tops with compression ratios varied by changing dish size. This design offers efficient flame propagation, superior detonation resistance, and high-compression ratios without excessive dome heights. On the small-block, compression ratios were decreased starting in 1971 from the previous nominal 10.25:1 to around 8.5:1 by increasing the combustion chamber volume and dishing the pistons. Assuming the head was cc'ed to minimum NHRA specs, a modern 9.5: 1 street engine compatible with presently available pump gas can be built by using early heads with the late short-block. Unfortunately, the heads in stock form cc nowhere near the "blueprint" specs, and milling them or the block upsets the stock non-adjustable valvetrain geometry. Mondello offers a line of forged pistons designed to produce 9.5:1 or 11.5:1 compression with "out of the box" heads.

What are the best "out of the box" heads? If you could find them, the 1967-'70 350 W31 design least 405585), which has a good short-turn radius on the intake ports and larger 2.005 intake/1.625 exhaust valves (compared to the standard 350 1.875 intake/1.5 exhaust), is the best bet among production heads. Since you probably wont find them, the "147" or "742" heads off a '68-'70 350 work fine, too. They have the smaller valves,but retain the good intake port. Naturally, larger valves can be added, even up to a 455's 2.072 intake.

After 1971, head quality declines. Not only are the chamber volumes high, but the intake ports have a sharp shelf. While all Olds production heads have siamesed center exhaust ports with a recessed divider, the recess is much greater on late smog heads. Late 1976 and up heads are drilled for 1/2-inch head bolts. To use earlier heads on the late blocks, their 7/16-inch bolt holes must be opened up. Late heads may be installed on earlier blocks. Due to water jacket differences, use the head gasket designed for the model year of the block not the head.

For all-out race applications, CJ Batten has designed a state-of-the-art Olds head that's cast in both iron (part No.22505143) and aluminum (part No. 22505805). They're available either from him or Olds dealers. Intake ports are enlarged and raised up. This requires a special Edelbrock Victor intake manifold (Edelbrock No. 2979). The best aftermarket intake for production heads is the dual-plane Edelbrock Performer (No. 3711), which "makes torque everywhere." Holley's Dominator is a tad stronger on the top end. Factory intakes work well through 5000 rpm. Pre-'72 versions are preferred, since they lack restrictive EGR passages. Original aluminum W31 intakes are identical to the cast-iron versions, but save 25 pounds. The only available small-block tunnel-rams are hand-fabricated by Dave Smith or CFE Enterprises. Right now, 260's must use the stock intake, since other aftermarket intakes won't match the 260's small ports. Manifold match-up also makes it difficult to run big-block heads on a small-block. While the tall deck castings physically bolt on, the intake port is taller than small-block manifold mating flanges. A bigblock head's larger combustion chambers will also lower compression by about one full point.

When it comes to camshafts, today's engines should use today's camshaft profiles that feature less overlap, decreased duration, and increased lift. While good in their day, the old factory W30 and W31 grinds are designed with lots of duration and mild lift. Not only can this cause problems with vacuum-actuated accessories, but they also won't work well in today's low-compression, weak-geared smog motors. Olds specialty houses now offer modern, computer-designed profiles tailor-made for Olds engines.

All Olds timing gears will interchange. Big-block chains are beefier than the small-blocks. An aftermarket roller is better yet. The water pump used in late air-conditioned cars (part No. 556283) features a superior low-drag impeller.

Big-blocks have been built with two different stroke lengths, connecting rod lengths, and piston compression heights (see chart). Main and rod journal diameters are the same for all big-blocks.

Since the 425 and 455-inch engines share the same bore size, but use different stroke cranks, the question arises, "Can a 425 be made into a 455 by swapping cranks?" Yes, but the different-length 455 pistons and rods are also required.

Both the short and long-stroke cranks have been produced in forged steel, nodular iron, and cast iron. Short-stroke forged cranks are relatively plentiful, but the long-stroke "943" 455 forgings are relatively rare.

The thickest blocks are early 455's stamped "FO" or (in the bellhousing area) "68 F". F1 or F2 blocks are a good second choice. Any of these can be bored to 4.25-inch without sonic testing. The '68-'70 455's used two different con rods, with the rare extra-heavy-duty version having more meat around the rod cheek and bolt head area. Other than this rare rod, all other big-block rods are identical from a metallurgical standpoint.

Big-block piston design is similar to the small-blocks-variations on a flat-top theme. With two basic combustion chamber sizes and two piston dish sizes, stock compression ratios range from 8.5:1 to 10.25:1. Early heads displaced either 70 or 85cc, with smog heads all having the big chambers. Use of a 70cc head on a late smog motor will raise compression about one full point. The 1970-'7l W30-type "F" heads had the small chamber, along with a good intake port. Unfortunately, they're scarce. Other early castings make a good alternative: Type "C" castings have an excellent intake port high nickel content, and the most material around the ports for hogging out. However, they do have 80 to 83cc chambers, and some 2-barrel versions have only 2-inch intake valves instead of the preferred 2.06 intakes. All big-blocks have 1.63-inch exhausts, except for Type J heads that had 1.690-inch exhausts. But the J heads have a poor "shelf intake port," as do the G and K castings. A, B, and D heads are acceptable subs for C or F castings, however. The larger valves can be installed in the small-valve heads.

Finally, there's the C J. Batten heads previously mentioned for the small-blocks. They'll bolt onto a big-block and really work great on the street or in race applications; but there's no off-the-shelf intake manifold available. Dave Smith can modify a small-block Edelbrock Victor to fit, or less expensive C.J. Batten spacers will adapt conventional big-block intakes, if some port misalignment is acceptable. For production heads, the old Edelbrock 04B dual-plane works best, but it's no longer available. Edelbrock plans to introduce a Performer eventually, until they do, if you can't find an 04B, stick with the stock cast-iron piece or its aluminum W30 duplicate. Any of these work better than the old 442 tri-power units, which should be considered only for restorations. Race-oriented packages usually use the Edelbrock Torker. Offenhauser offers the only off-the-shelf tunnel ram but its passages at the carb end are way too small for all-out engines. Dave Smith offers his own custom tops for this intake, or complete ground-up tunnel rams.

Nothing more needs be said on cams-the same rules apply as on a small-block. Modern profiles cream the old '60s stuff. When properly cammed and built according to the Olds experts guidelines, the big-block Olds will produce an ungodly amount of torque, yet still runs well on available pump gas while delivering exceptional mileage for its displacement. Even better, they'll bolt right in place of existing Olds small-blocks. Cores are plentiful and cheap. Cutlasses and Omegas are cheaper than Chevelles and Novas. Olds blocks are cast from better material than the competition's, resulting in better long-term bore wear. Olds specialty parts houses have solutions for the oiling and valvetrain problems. Still don't think Oldsmobiles make serious performance cars? Check out who is the NHRA manufacturer's champion. (It isn't the Bow-Tie boys!) Maybe it's time you built yourself an Olds Rocket-ship!

Oldsmobile Engine Specifications:

       CID  YEARS    BORE   STR.   Jrnl. Mains  Conn.  Piston	
                                   Rods  Dia.   Rod    Comp. Ht

SMALL- 260  1976-82  3.5    3.385  2.12  2.5    6.0    1.615
BLOCK  260D 1979-80  3.5    3.385  2.12  3.0    5.886  1.770
       307  1980-86  3.8    3.385  2.12  2.5    6.0    1.615
       330  1964-67  3.938  3.385  2.12  2.5    6.0    1.615
       350  1968-80  4.057  3.385  2.12  2.5    6.0    1.615
       350D 1978-85  4.057  3.385  2.12  3.0    5.886  1.770
       403  1976-85  4.350  3.385  2.12  2.5    6.0    1.615

BIG-   400  1965-67  4.0    3.975  2.5  3.0     6.998  1.615
BLOCK  400  1968-69  3.870  4.250  2.5  3.0     6.735  1.74
       425  1965-67  4.125  3.975  2.5  3.0     6.998  1.615
       455  1968-76  4.125  4.250  2.5  3.0     6.735  1.74

Cam Bank Angle And Tappet Diameters:


1964-67   330  ALL          .842       39deg
1965      400  ALL          .842       45deg
1965      425  ALL          .842       45deg
1966-67   400  ALL          .921       39deg
1966      425  exc.Toronado .842       45deg
1966-67   425  Toronado     .921       39deg
1967      425  exc.Toronado .842       39deg
1968-69   400  ALL          .842       39deg
1968-80	  350  ALL (gas)    .842       39deg
1968-76   455  ALL          .842       39deg
1975-82   260  ALL (gas/dsl).842       39deg
1977-79   403  ALL          .842       39deg
1978-80   350  ALL (diesel) .842       39deg
1980-84   307  ALL          .842       39deg
1981-85   350  ALL (diesel) .921       39deg
1985-86   307  ALL          .921       39deg

Olds High-Performance Specialists/Parts:

Batten Heads
27554 Wick Rd.
Romulus, MI.  48174
(313) 946-9850

Kenne-Bell Enterprises
1527-K W. 13th St.
Upland, CA.  91786
(714) 946-7671

Mondello Performance
8166 Orion Ave.
Van Nuys, CA.  91406
(818) 994-6910

Prescription Performance
17 Grassy Pond Dr.
Smithtown, NY.  11787
(516) 543-2519

Dave Smith Engineering
112 N. Manchester
Anaheim, CA.  92802
(714) 635-3100