Small Block Chevy Engines - 3-Way Small-Block Showdown

3 Staffers, # Builds, and a Whole Lot of Bench Racing

383ci Stump Puller
There's nothing like being put on the spot to make a guy define his priorities. Case in point: getting two weeks to spec out and create a $5,500 small-block. Actually, it didn't take much more than a few minutes for a list of desirable qualities to crystallize in my sleep-deprived brain. Right off the bat, I wanted an engine I could actually put to use: street, strip, autocross, open-road racing. A dyno bullet would not do. Second, I've been enamored of the Gen III LS6's powerband since my first drive in a Z06, so I was looking for a Kansas-flat torque curve with a horsepower peak to match. Getting into the 450-plus range for each would be good--higher than that would be better.

Third--and this was the curveball--I wanted this engine to be capable of passing at the pipe if I decided to slip it under the induction system of an '80s smog car. Not that I endorse that kind of thing, mind you. But it's an interesting exercise...

The recipe, as I saw it, called for a stout but not over-the-top bottom end, a heavy-breathing top end, and as much cam as we could get away with. The cam and heads combination proved to be key. Dart's 215cc Iron Eagle Platinum Series heads are relatively inexpensive, but the flow numbers they generate make them an outright bargain. We chose a Comp hydraulic-roller cam for long-term reliability, but the chosen 'stick would have to make the most of the heads' efficiency. Our duration figures are fairly stout for a street cam, and the lift numbers are up there, but keeping the lobe separation at 113 degrees allows for adequate vacuum and a livable idle, and makes the engine relatively emissions friendly.

Relying heavily on the knowledge and experience of Speed-O-Motive's George Ullrich, my LS6-style traditional small-block became a reality. The peak numbers of 470 lb-ft and 458 hp are about as close to equal as you can get--more importantly, this baby is making more than 400 lb-ft from 2,500 rpm all the way to six grand. Acceleration on demand throughout the powerband, but plenty of horsepower for top-end haulin'--this engine would make a good-handling car an utter riot to drive. And isn't that the whole purpose of building a hot engine?

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Speed-O-Motive bases its heads on bare castings, which are machined before assembly. In our case, this meant taking a couple of thousandths off the surface of our 215cc Dart Iron Eagle Platinum heads. The heads were then assembled with Manley valves and seals, along with cam-matched Comp springs and valvetrain components. The Dart heads feature machined spring pockets, but S-O-M uses locators for improved durability.

We used S-O-M's forged rods, which were all balanced to within 0.5 g of the lightest piece. What kind of weight is that? A dollar bill weighs 1 g. That's tight.

Since we used a hydraulic-roller 'stick, a cam button was needed. Bill ground strategically placed flats into the button to ease installation--and removal--for adjustment to 0.003-inch endplay.

Mahle's Power Pak pistons are exquisite forgings that look almost too nice to put in an engine. Each slug was also balanced to within 0.5 g of the lightest. Finding the best place to take material from required some careful measurement.

Although we ordered the specified Comp Cams pushrods for our application, Bill still checked for proper valvetrain geometry before installing our rocker arms. These lines across the center of the valve indicate that we're right on.

We used S-O-M's steel roller rocker arms. Going to a 1.6:1 ratio increased our cam lift to take advantage of the deep-breathing Dart heads.

If you've never strapped your own engine down to a dyno to see what's what, we highly recommend the experience. The only thing better than seeing it is running it.

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