More power is the universal dream of hot rodders, and bolt-ons are the easiest way to add that power. One of the most common questions we're hit with is exactly how much power are various bolt-ons worth? So we teamed up with Kevin McClelland and John Wilson of Flowmaster's Research and Development dyno lab to stage a series of tests to reveal just what power gains could be generated from typical upgrades on an average engine. We started with a stock engine and made changes in an order that would be easiest for you to duplicate and would also provide the best gains for each step.
BASELINE
We're assuming that you have a stock engine in your car that runs fine but could use a little more get up and go. To duplicate this but also guarantee that we could finish all of our testing without an engine failure or being concerned about a worn engine affecting our results, we freshened up a 350ci Chevrolet. We had Jim Grubbs Motorsports perform only basic machine work and avoided anything that would give this engine a performance advantage, such as decking the block. In fact, the pistons ended up an average of .035 inch below the deck surface of the block. Combined with 76cc combustion chamber heads (stock unported 882 castings), .041-inch-thick head gaskets and 6.1cc valve-relief pistons (TRW Power Forged L2256 flat-tops), the compression came to a wheezing 8.40:1. If your engine has dished pistons, then the compression is even lower. We used Sealed Power parts to rebuild the engine (the aforementioned TRW pistons, Federal-Mogul bearings and Sealed Power gaskets, oil pump and rings). We also used ARP fasteners, including an accessory kit that provided all external engine fasteners, a head-bolt kit made specifically for O.E.M. cast-iron and Brodix -8, -10, -11 and -11XB cylinder heads (part No. 134-3601), and Wave-Loc rod bolts.
We baselined the engine with a stock replacement camshaft from Sealed Power (which also carries a full line of original-profile and modern high-performance cams). The rest of the valvetrain retained the used stock pieces. The exhaust was comprised of 2-inch-outlet iron manifolds with 2-inch tubing and new replacement-style mufflers purchased at a local auto parts store. We used a '69 cast-iron four-barrel manifold and an early Q-jet carburetor.
TESTING
The engine was broken in and several dyno pulls were made to ensure that the engine data would be repeatable. We changed one part at a time and made at least two dyno pulls after each swap. While a total of 38 pulls were made on the engine, the 12 most representative tests are printed here (two tests per graph). The timing and the fuel mixture were optimized for each combination throughout testing, though few of the parts swaps demanded much change.
Something that might surprise you is how little power the engine made in stock form. In the real world, this is very typical of what you can expect from stock V8 engines of this displacement and compression. Also, our finished engine with its aluminum heads and roller rockers may not make as much power as you would expect, but remember that we didn't do anything except bolt parts onto it. Improving the quench and compression ratio would greatly improve the power, but the real point of this article is to show how much you can upgrade the existing engine without removing it from your car. This engine's generous torque curve and respectable horsepower would make the car a fun daily driver.
