The 1970's, The Emissions Decade

If the 60's were then pinnacle of the small block Chevy's development at the time,the 1970's would test the engines ability to endure politics both intra-office and government. Emissions were to become a major performance inhibitor. During the 60's the Motor Vehicle Pollution Control Act and the Clean Air Act were passed and they started to affect how manufacturers had to build vehicles. In 66 Vehicles were built specifically for California and then the rest of us. The 1970 model year would be the last of the high compression high performance small block. By 71,the compression ratios had to be dropped from 11:1 to 9:1 for the famed LT-1 and to an average of 8.5:1 for the standard small block. The 71 LT-1 was rated at 330 Horsepower for the Camaro and 350 Horsepower for the Corvette. One of the benefits of lowering compession ratios is that it emilinated cylinder wall and cylinder bulk head cracking. 1972 comes along and the big three all adopted the S.A.E. net horsepower rating formula. This lowered horsepower numbers by itself because manufacturers had to advertise the engines net horsepower numbers instead of the gross. Chevrolet and the rest of the manufactures felt that the decline in the performance market was a direct result of the decline in availability of performence engines from the factory. Everyone was weathering the storm of emissions coming into play in 1972 when the E.P.A. were leaking out that they were going to enact fuel economy standards. An interesting thing to note at this time, while street car performance interest was falling,the interest at the tracks around the country was on the rise. Sanctioned racing became very popular in the 70's. It was during this time that Chevrolet increased their popularity with racers even more than in the 60's. There was a lot of guys working at Chevrolet that were racers,it's thanks to them that they ket a lot of the key performance engine parts were still manufactured. These parts were readily available right from the dealership parts counters.

The Small Block 400.
Believe it or not the small block 400 was actually being researched and developed prior to 1968. Things like increasing the main journal diameter to 2.65 in and cutting down the bolt boss height on the connecting rods were a requirment to make the engine work. This engine was also the first small block made available with 4 bolt mains right from the start of it's production. This is partly because of the higher thrust load on the bottom end berings,the high rod angularity, and to provide more strenght limiting the amount of deflection in the crankcase. At first the thought of building the small block 400 was thought to be a stretch considering cylinder wall thickness and thus the engineers at Chevy blended the bores or what was dubbed "siammeseing" with is the term most of us hot rodders use now. These engines were also only avaliable with an automotic transmission to back them up to limit the shift speed of the tranny thus controlling the revs of the engine. These engines came out with 330 Horsepower with the RPO number LS3 and 265 Horsepower LF6 in 1970. What was really attractive about the small block 400 was the boatloads of torque.  Little did anyone know at the time but,racing enthusiasts and hot rodders alike would have a heyday with the crank and rods from this engine in the future that would lead to the creation of the 383 small block Chevy. The bore of this engine was 4.125 in and the troke was 3.75 in. The engine would be in production until 1977.

Cross section of the small block 400

The LT1 in 1970 for intended to take over the perfomance title for the 327. For the 70 model year this engine was built with the best parts available. Forged connecting rod,steel forged crank,forged aluminum TRW pistons with a mechanical 458 lift "LT1" Camshaft. The cylinder heads where the 2.02/1.60 closed chamber 64 cc heads machined for screw in studs and guide plates. A high raise Aluminum intake and a 780 Holley topped it off. And if you were lucky you got it with the "Winters" snowflake embossed on the intake. Chevy considered this particular small block to be the best they ever built to that date.

In 1975 they introduced the 265 and it was basically a boat anchor. And everyone from Chevrolet agreed.

The 305
Introduced in 1976, this displacement came from using the 3.48 inch stroke and a 3.74 inch bore. Allowing for a 1.84 sized intake valve. This engine was to take over as the base Chevy small block to suit the EPA standards for fuel economy and emissions. Believe it or not the 305 was the result of a lot of design and tested. Bore/stroke ratio is very important when it comes to and engine being either over square or under square. An over square engine requires engine spark to be retarded to the point where it kills the efficiency of the engine.That increases the exhuast gas temperature,burning unspend gases in the exhuast,good for the air,bed for fuel economy and power. The 305 was a more square engine thus meeting the emissions requirments and get decent fuel economy. However the 305 was only intended to be a 2 barrel carburetor engine and was sold as such until 1979 when the engineers at Chevrolet had tuned to configuration well enough to handle the spark advance required to make the engine efficient. Hoeever,it would be a few years yet before the 305 would shake the reputation of a slug and become a potential performance engine.

Now the lessions lerned from development of the 262 and 305 lead to the development of the 267. The only real noteworthy thing about the 267 was the square bore/stroke ratio. This engine was sold in the Monte Carlo and Malibu in California and a few other states. The engine turned out to be one of the most fuel efficient and cleanest burning motors available to date however Chevrolets research and development of the V-6 engines would negate such a small displacment small block V-8.

  Overall,there were a lot of people fully believing that the V-8 was going the way of the dinosuar,there were groups of people thinking that we were going to run out of oil and that the North American love affair with the car was going to come to an end. They couldn't have been more wrong.

1967 SS Chevelle

Although there wasn't a lot of info for this 67 Chevelle. I'm going to let the picture speak for themselves.

  The 396 was the only available power option if you wanted for power than the 327. All things being equal though,the 327 would beat the 396 in quarter mile times when thy were installed in the same cars.

The Small Block Chevy in the 60's

The 1960's were great years when it came to further development of the small block. The 327,302 and 350's that were developed produced fantastic horsepower numbers never seen yet in engines of these displacements.So let's get into what happened during this decade when it came to the small blocks performance. During this decade the small block would be installed in almost every type of race car built at the time including Ferrari's,Maserati's to the American built Chaparral. Even British built Lola's were eventually built using the small block Chevy. The light weight,durability and power potential made it idea for these race cars

 
   The 327
This displacement wasn't something that the engineers at Chevy actually thought about until it came to their attention that racers were boring and stroking the 283 with suprising results. The 283's 3.87 inch bore was thought to be the limit. And considering that the original small block design was simply to accommodate 265 C.I.D. The 327 would be the first engine to be designed and built at the Chevrolet engineering Center. The first ones were tested pretty much at the beginning of the decade. After problems like core shift and oil consumption were dealt with the engine was made available for the 62 model year. The engine had a 4.00 in bore,3.25 in stoke and retained the journal sizes of 2.30 in mains and 2.00 in rods from the 283. The increased bore and stroke gave some pretty impressive horsepower and torque numbers. When the engineers started installing bigger cams,performance cylinder heads that were ported and then added the "Dog House" fuel injection they pushed the numbers up to 360 HP! This engine powered the 1963 Corvette to a 14.5 second quarter mile time. There was also no factory installed small blocks in the Chevy II's. That wasa dealership option that allowed either the 283 or 327 with the recessed oil filter boss. The 327 would top out at 375 Horsepower with the fuel injection option.

While the 327 was being designed there was also work going on with another small block that actually got its start in the later part of the 1950's as a test platform for performance parts that went out the back door through SEDCO.Something put together by Vince Piggins, one of the guys that worked at Chevrolet during the time,more on him later. SEDCO was a low profile way to get newly developed performance parts out to the guys doing the racing and backyard engine building. Anyways, the 302 was actually built as this test platform using a bored out 283 prior to the 60's and by 1961 the block had enough strength to actually handle the 4.00 in bore.

There are a great many innovations that came out as a result of testing the performance including "Cowl Induction" and what is now the 'Cold Air Intake" And by this time it was well established that the term "Small Block" & "Big Block" were terms coined specifically as a result of engines built by Chevrolet. When the 302 was made available it was installed into the all new Z-28 Camaro. There was a specified amount of Z-28's made available to the puplic because it was part of the SCCA Trans Am rules. The engine was rated at 290 Horse power for the street however actual dyno numbers like 340,350,375 and 390 have been tossed around. The 302 built by Traco for the racing series dyno'd out at around 500 horsepower. And it would rev like no tomorrow making it pretty much perfect for the Trams Am series racing.

Specs for the 302 went something like this,

Aluminum Intake

11:1 compression

2.02/1.60 closed chamber heads

800 CFM Holley

Forged Pistons

Duntov "30/30" Cam

Steel Forged crank

And what was known as a Tuffriding Surface treatment.

The 350 Chevy
By now with the small block's power potential reaching 365 or so horsepower the engineers at Chevy were given the task of possibly enlarging the small block even more. Now remember it was only a few years ago the 327 appeared and the engineers and testing guys felt comfortable with the displacement of the 327.  So the engineers designed and built a 3.47 in stroke crank and the 350 was born. Now when people talk about a "small block Chevy" this is the motor they're referring to. Now,along the course of the development of the block itself, the area where the crankshaft rotates had been changed a number of times and for the 350 it was no exception.By raising the lower end of the bore and making sure there was enough room inside the panrail area for the larger rotating mass. This also created the need for the main and rod jounal size to be in creased and thus the "large journal" crank was developed.

  Now back when this writer was growing up the 327 was considered the ultimate small block. This may have been a result of the 350 debuting with 295 horsepower. The smaller 327 was still cranking out 360 or so HP.  There were a number of problems that arose with the 350 after it was in production. After these issues were addressed the 350 went on debut in the 1967 Camaro. By the begining of the next decade the 350 would become the most powerful small block ever built with the LT-1 RPO designation. It would take 22 years before the small block would surpass the original LT-1's power.

 The 307
With power demands for the basic small block increasing the 283 witch was considered powerful only 10 years before was given a fresh work over with a 327 crankshaft. This didn't create a power monster, the engine was never available with any performance options. However,it doesn't take much to increase the small blocks power with just a few go fast goodies like a manifold and a 4 barrel carburetor and given the 3.25 in stroke it had an almost perfect rod/stroke ration for an accelleration engine. The 307 because the base engine for Chevrolet's passenger cars and truck line up.