150 HP for a 305 Chevy Engine - Hate Me

Obviously, cam and valvetrain would be part of the strategy. With the engine's small-displacement and undoubtedly compromised compression ratio, too much cam would be counterproductive. Since this is a flat-tappet engine, we decided to stay with that type of camshaft, as opposed to a retro-fit hydraulic roller, which would have been considerably more costly. Had this been a higher compression roller block, we definitely would have gone with a more aggressive hydraulic roller camshaft. While erring too big would ruin the build, erring too small is also a mistake-one that would curb peak power. After much consideration, a COMP XE268H flat-tappet hydraulic was chosen. This cam allows a smaller engine to make power up into the 6,000-plus rpm range, yet its relatively short duration, at 224/230-degrees, preserves cylinder pressure and maintains acceptable street idle quality. For a general purpose real street cam, this stick is hard to beat. The final components of our 305 power package related to the induction system. This engine was a carbureted unit, and we intended to keep it that way. Later 305s had some form of fuel injection, but for all-out power and a broad rpm range, a properly chosen carb/manifold will out-gun the factory EFI stuff, and is far more cost effective than a trick aftermarket injection setup. The manifold decision was easy, since the Edelbrock Performer RPM AirGap consistently shows the capability to make good peak power, while having much better torque than a single plane. With the 180cc EQ heads, the AirGap would be a perfect match when considering the port sizes. To top the manifold, we decided upon a 650-cfm Speed Demon carb, a good general high-performance carburetor, in a flow capacity that seemed about right for an engine of this displacement.

The Test
We had essentially mapped out our entire modification plan before hitting the dyno, a basic heads/cam/induction package that we figured would breathe life into one of these underachieving mills. For a baseline combination, the engine was all stock, including the short-block, heads, cam, a cast iron GM two-plane intake manifold, and a Quadra-Jet carb. As the engine was docked to Westech's SuperFlow 901 dyno in this form, the engine's virtue was disparaged as is usual for 305s. The scuttlebutt indicated the engine would be well short of the 200 hp mark, except for one optimistic passerby who put the number at 275. Well, the engine was being tested bare of all of its factory smog equipment, through excellent long-tube dyno headers, and with an electric water pump in place of the factory belt driven accessories. My 225 hp guess proved to be pretty close, with the 305 delivering 221 hp at 4,800 rpm, and 291 lb-ft of torque at 3,200 rpm. Normally, we like to make changes one step at a time, but in this case, we planned to make the changes all at once. There seemed to be no use in trying to run the good heads with the tiny stock cam, and the big cam with the junk heads also seemed like a dog of a combination. Finally, we weren't going to add a good set of heads and a hot street cam, and then cap it with a stock iron intake. This program was more of a full power package, so with the baseline numbers in, we stripped the 305 to the bare short-block and got to work. The heads were bolted on using Mr. Gasket's thin 0.018-inch head gaskets, actually the same set that had been under the stock 305 heads. The COMP cam got a new set of COMP's standard hydraulic lifters, along with COMP's pushrods and their Pro Magnum steel rockers. Shaver's supplied the rocker studs and guide plates that work with these heads, and before long we were bolting on the Edelbrock Vortec AirGap intake and hooking the linkage to the 650 Speed Demon carb.

What would the 305 make? We had plenty of time for conjecture while the engine was being run for the cam break-in cycle. Even though the stock 305 had show better output than most of the detractors had anticipated, there was little confidence in the 305's potential. Jawboning in the cell predicted numbers in the low 300hp range. There were a few surprised expressions when the 305 cranked 367 hp at 6,000 rpm on the first pull. With some fine-tuning of the air/fuel ratio via a jet change to the Speed Demon carb, power inched up to 372 hp at 6,100 rpm. That's credible power for any street small-block; enough to make a Third Gen Camaro really scoot. Had we started with a higher compression hydraulic roller 305, as is typical of the later F-bodies, there likely would have been even a little more. The lesson here is that any engine can be made to perform with the right combination of parts, even those that the vast majority of people are reluctant to love.