Photo Cutline: General Motors offered a 1971 Corvette LS6, but never installed the successor LS7 454 in Chevelles or Corvettes. Due to the higher gas prices, insurance concerns and upcoming new smog and unleaded fuel mandates, GM only offered the LS7 as an ³off road use only² crate engine although a similar design is still available today called the 454 HO from GM Performance. (Photos/advertisements compliments of General Motors Chevrolet division)

 

Q: Greg, I have a question on an engine that I figure will be a piece of cake for you, but for the life of me I can't run into a person that can answer it. I bought a 69 Camaro from a guy in Texas with an old Chevy crate engine in it called an LS7 Big Block. He installed the LS7 in the car in the late 1980's and the number stamped on the block is TL02XCH09488093.

 

I would like to know when this motor was manufactured. I think they quit producing them when the 502 came out in the 1990's. The Texas guy worked at a Chevy dealer and he bought it over the counter under part #3965774. Thanks if you can solve this puzzle for me! Bob Killian, via email.

 

A: Bob, I say with humility you came to the right person! I bought this exact same crate engine in March of 1979, part #3965774, from RC Campbell Chevrolet in Shamokin, Pa. for $1497 total.

 

It was a special high-performance 454-inch big block engine that I put into my 1972 Vega econo-funny car coupled to an ATI Turbo 400 transmission and converter. In pretty much stock form, I proceeded to run a best of 9.6 seconds at just shy of 140 mph in the quarter with a single 800 Holley four-barrel carb. The only change we ever made was try a few different flat-tappet cams, notably Isky and Comp Cams, both with great results (one went quicker, the other faster).

 

This LS7 engine was supposed to be the successor of the potent LS6, 425-horse Chevy engine that appeared in the 1970 Chevelle LS6 454 line and the following year in just 188 LS6, 425-horse 1971 Corvettes. These Corvettes were ³sneaked through² as a $1,221 RPO option even though 1971 found higher gas prices, higher insurance rates and soon to come smog and unleaded fuel mandates that had many manufacturers gearing up (or should I say gearing down) for. And it was because of these horsepower robbing mandates and declining condition of the muscle car era that Chevy pulled the plug on inserting the LS7 into Chevelle and Corvette models.  

 

Thus, part #3965774 was born, and Chevy sold thousands of these ³off road use² only engines to enthusiasts and pre 1972 muscle car owners. By the way, your 1969 Camaro is fully street legal with this engine, as there were no catalytic converters and smog engine mandates that decade. 

 

Additionally, part #3965774 454 LS7 engine was a ³long block² crate engine, which means it came less intake manifold, distributor, ignition, carb, starter and water pump. But oh my, what a buy it was back then. 

 

The engine specifics include cast iron open chamber rectangular port cylinder heads with 2.19 intake and 1.88 exhaust valves, ³dimple² 7/16 bolt steel rods, and forged 12.25 compression pistons. The cam is a flat tappet solid lifter 560 intake and 600 exhaust design, necessitating setting the valve lash regularly for ultimate performance.

 

The block featured four-bolt mains, and the ³XCH² nomenclature in your stamped block number is proof it is indeed an original LS7 block. The bottom end finds a forged steel 4.0-inch stroke crankshaft that is externally balanced, meaning Chevy made special flywheels and harmonic balancers weighted specific to the 4.0-inch stroke crank.

 

Every other big-block ever produced had an internally balanced 3.76-inch stroke crank, be it 366, 396, 402 or 427 design. If you happen to put a 396 flywheel on a 454 crank, it will vibrate badly until you figure out you messed up. (I had a friend who did this and had no idea why it vibrated so badly).

 

Today, GM Performance offers numerous crate engine applications, up to 572 inches in big block form at over 700 horses. And, even though part #3965774 has long since disappeared, it is replaced by what I feel is the modern day LS7, called 454 HO and part #12568774. This 454 carries nearly all of the exact same engine pieces in your engine albeit with lower compression 8.75 to 1 pistons and a tamer hydraulic roller camshaft.  This 454HO uses modern 92 octane pump gas, generates 425 horses and 500 lb. ft. of torque and retails for $7,158 at your local Chevy dealer or performance retailer.

 

Thanks for your kind words, and for reading my columns.

 

---

---