It's a great time to be part of the performance world. With a decent budget, a good long-block, and the right bolt-on parts, you can easily raise your engine's power level into the stratosphere. We wanted to see how much extra power we could uncover from our pal John Barkley's 391small-block. A few years back, he assembled a long 3.82-inch-stroked Eagle crank and a 0.030-inch-over 350 block to power his street-driven '71 Camaro. This existing combo included a seasoned set of AFR 190 cylinder heads atop a good dual-plane intake manifold, and a 670-cfm vacuum-secondary carburetor. To actuate the 2.02/1.60-inch valves, Barkley had stuffed in a hydraulic roller camshaft with 217/225 degrees duration at 0.050 inch lift with 485/505 inch valve lift.
The engine provided reasonable performance, but Barkley wanted hordes of steam because he'd recently acquired an '80 Camaro that he wanted to race as a bracket car. Since the Camaro was equipped with 4.88:1 rearend gears, he wasn't really concerned with low-speed drivability but rather with midrange to top-end power. This meant his camshaft, intake manifold, and carburetor would need to provide increased breathing at higher engine speeds.
So with a pencil and pad, he mapped out a big power combo to transform his mild 391 into a heavy-breathing powerhouse. At the heart of his plan was a very stout solid roller camshaft from Lunati with lots of lift and duration. Since he wanted to move the powerband up, he decided to put the proven dual-plane manifold on the shelf and chose a Holley Strip Dominator intake manifold featuring a large open-plenum and big runners for strong power above 4,500 rpm. To provide fuel, Barkley thought either a Holley 830 HP or 950 HP carburetor would do the trick. Now all he needed was some dyno numbers.
Once the performance goodies were in hand, we followed along as Bob and George Vrbancic of Vrbancic Bros. Racing in Ontario, California, bolted on the parts, fired up the dyno, and recorded where the power needles stopped. After a day and a half of testing and tuning the 391, the dyno recorded an impressive gain, from 411 up to 537 horses. What's more, this was all done for about $2,700. Lots of power for a reasonable amount of dough. That's a pretty solid plan.
Quick Notes
What we did
A manifold swap and a solid-roller conversion
Bottom line
An easy recipe to make over 500 horses from a big-inch small-block
Cost (APPROX)
$2,660 | 
From 391 inches this engine developed 537 hp at 6,400 rpm.AFR cylinder heads featured 190cc intake ports and 2.02/1.60 valves, and were milled 0.035 inch to reduce combustion chamber size from 76 to 70 cc. While these are no longer available, AFR has replaced them with an improved 195 version.Valve lash was set to the specified 0.016/0.016 inch.A Milodon wide-sump oil pan and a Diamond stripper windage tray offer superior oil supply.A single Holley 950 HP carburetor provided air and fuel for excellent midrange and top-end power.The Holley Strip Dominator intake manifold is a single-plane designed to improve mixture flow for optimal power above 4,500 rpm.Reciprocating assembly included JE forged pistons, a 3.832-stroke Eagle crankshaft, and 5.70 Eagle rods. | 
In base trim, Barkley's engine was equipped with a small 670-cfm carburetor, a divided-plenum intake manifold, and a small hydraulic roller camshaft with 217/225 degrees duration at 0.050 inch lift, a 112-degree lobe center, and 0.485/0.505 inch valve lift. Inside the carb were 68 primary jets and 80 secondary jets with a 6.5 power valve. Although this combo did not make nearly as much horsepower as the final combo, it was a great street package that produced an average of 453 lb-ft and 411 hp at 5,200 rpm. |