No matter how much engine-building experience you have, there's always a little doubt until you hear your latest combination run. We knew we had done our homework, though, and our LS7-killer fired on the first hit of the starter. Since our Comp roller camshaft didn't require any special break-in procedure, we tuned the idle circuitry of our shop carb and checked for leaks, then ran the engine between 2,000 and 3,000 rpm, applying a varying load with the dyno servo to help seat the piston rings. With that procedure accomplished, it was time for the true test of our research: making a dyno pull to see how much power our old-school small-block would really make.
We decided to make a conservative pull on our first attempt, using the 750 carb, setting our ignition timing at 30 degrees total advance, and only revving the engine to 5,500 rpm. In general, loading the engine for the first time should expose any weaknesses, so simply making it through this pull indicated that ours was healthy and ready for some real testing. Glancing at the numbers from the conservative first pull, we noticed that we were already making nearly 500 lb-ft of torque at 4,800 rpm and more than 500 horses at 5,500 rpm—and we hadn't even performed any tuning or installed our Quickfuel 950 yet. Realizing that our engine clearly had the potential to blow away the LS7, we got busy tuning.
After installing our Quickfuel 950 and adding 2 degrees of ignition timing, we made another pull up to 6,500 rpm, netting 519 lb-ft of torque at 4,700 and 573 hp at 6,500—handily topping the LS7 in both measures. Further, our oxygen sensor and exhaust temperature data indicated our mixture was still very rich and the engine needed more ignition timing. By adjusting timing, jetting in our Quickfuel Q-series carburetor, and eventually switching to a Quickfuel 1,050-cfm QFX 4700 carb, we gained power on each successive pull, adding to our already huge output advantage.
Our not-so-small small-block eventually made a best pull of 537.7 lb-ft at 5,000 rpm and 613.3 hp at 6,500 rpm. Even better, it had a very broad torque curve, making more than 500 lb-ft from 4,400 all the way up to 6,300 rpm. Horsepower topped 600 from 6,200 all the way to 6,700 rpm, but it didn't fall off dramatically from there, only dropping to 596.0 at 7,000.
In summation, we're very happy with the performance of our 427-cube SBC, especially in relation to the LS7 we were tasked with targeting. This powerhouse should be a blast in C3 Triple-Ex, ensuring rapid acceleration and even shaving some 200 pounds from the nose. Driveability should be great as well, especially considering we've already installed a Tremec five-speed and will have the ability to pull into any gas station to fill the tank with premium unleaded.
If you're considering repowering your Stingray, you might want to consider a traditional small-block Chevy. Ours topped the LS7's performance by more than 108 horses, and it won't require any special engine mounts, headers, or fuel-system parts to bolt right into our '71 edition. Look for future articles detailing our experimentation with cam timing, carb spac-ers, valve lash, and tuning while on the dyno, and be sure to log onto www.vetteweb.com to let us know what you think of our engine build.