391ci Small-Block - Tech - That's Solid
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.
391CI Build Sheet
Specifications not listed are the same as stock. Except as noted, all dimensions are in inches or fractions thereof.
Bore x stroke4.030 x 3.832Compression10:1Valves2.02/1.60Rod, center-to-center5.70Chamber volume70cc (milled 0.035 to achieve from 76cc)Rod-bearing clearance0.0024Crank endplay0.0045Piston ring end gap0.024 top; 0.018 second
CAM SPECSManufacturerLunati PNLUN-60133TypeSolid rollerValve lift0.585/0.600 w/ 1.5:1 rockers; 0.624/640 w/ 1.6:1 rockersDuration at 0.050 inch249/255 Lash0.016/0.016 inch, intake/exhaustLSA110 degrees
Flow Numbers
Although Barkley's 190 AFR cylinder heads have been discontinued for about five years, we did manage to dig up one of our old catalogs to learn the published flow numbers, measured in cfm.
LIFT0.2000.3000.4000.5000.600INTAKE129195240260262 EXHAUST108156178190194
Bolt-On Parts Cost
All prices sourced through summitracing.com, except where noted.
MFGPNDescriptionPriceHolleyHLY-300-25Intake manifold, Strip Dominator, single-plane$180 80509-1 830 HP carburetor$680 80496-1 950 HP carburetoror $700LunatiLUN-60133Voodoo solid roller camshaft$309 LUN-72402LUN Pressurized solid roller lifter, priority oiling system$586 LUN-931153-keyway roller timing set, double roller$141 LUN-74620 K2LUNSprings, locks, and retainers $348Manley25722-1651/416-inch push rods 8.100-inch$140Moroso*MOR-64980Carburetor Spacer, Aluminum, 1-inch$42Scorpion**SCP 10031.6, 71/416-inch, roller rocker arms$215 TOTAL$2,661*Sold through Vrbancic Bros. Racing
**Sold through Scoggin-Dickey Parts Center
Dyno Details
Headers 1 3/4-to-1 7/8 Hooker Super Comp step headers
Fuel 91-octane
TEST 1RPMLB-FTHP3,5004713143,6004703223,7004693303,8004673383,9004 683484,0004713584,1004723684,2004713774,3004693844 ,4004643894,5004603944,6004563994,7004504034,80044 34054,9004364075,0004304105,1004234115,2004164115, 3004074115,400398409AVG TORQUE 453AVG POWER339
* Holley carb 670-cfm (PN 90670)
* 68P/80S jets
* Power valve: 6.5
* Dual-plane intakemanifold
* Hydraulic roller camshaft with 217/225 degrees duration at 0.050 inch lift
* Advance: 36 degrees
TEST 2RPMLB-FTHP3,5004683123,6004683213,7004643273,8004603333,9004 563394,0004583494,1004683654,2004783834,3004863984 ,4004934134,5004964254,6004984364,7004994464,80050 04574,9005034695,0005044805,1005054915,2005044995, 3005015065,4004995135,5004935175,6004885205,700482 5235,8004765255,9004695276,0004635296,1004575306,2 004515326,3004435306,4004365296,500430527AVG TORQUE477AVG POWER454
* Holley carb 950 HP
* 78P/78S jets
* Power valve: 6.5
* Holley Strip Dominator manifold
* Lunati solid roller cam
* Scorpion 1.6 roller rockers
* Advance: 36 degrees
TEST 3RPMLB-FTHP3,5004703133,6004673203,7004613253,8004593323,9004 593414,0004633524,1004733694,2004843874,3004904014 ,4004964154,5004984274,6005004384,7005024494,80050 54624,9005074735,0005094855,1005094955,2005095045, 3005055105,4005025165,5004975205,6004915235,700485 5265,8004795295,9004735316,0004675336,1004605356,2 004535356,3004475366,4004415376,500433536AVG TORQUE457AVG POWER480
* 76P/76S Jets
* 1-inch open spacer
* Advance: 34 degrees

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