Dyno Test: '67 390
Owner: Jamie LaPage
390 High Performance, C6 automatic
Jamie LaPage arrived at Jon's shop with a rough idle and poor performance for a 390 High Performance V-8. Jamie's 390 has an aggressive hydraulic camshaft, which adversely affects idle quality. What's more, there's an Autolite 4100 on top of an Edelbrock Performer 390 dual-plane manifold. These modifications aren't a bad thing, but without proper tuning, they can adversely affect performance.
Pull 1: Baseline
Peak horsepower: 193.30 at 3,750 rpm
Peak torque: 270.66 lb-ft at 3,750 rpm
Air/fuel ratio: 12.8:1 at 70-mph cruise; at wide-open throttle, 11.0:1
Jon checked out Jamie's 4100 carburetor and concluded it was not calibrated for altitude but ran the 390 anyway to establish a baseline.
Pull 2
Peak horsepower: 198.0 at 4,700 rpm
Peak torque: 264.32 lb-ft at 3,650 rpm
Air/fuel ratio: 14.0:1 at 70-mph cruise; at wide-open throttle, 12.5:1
Jon pulled Jamie's 4100 and replaced it with a remanufactured 4100 from Pony Carburetors calibrated for the thinner air in Las Cruces. Horsepower went up but torque went down. However, we experienced a broader torque curve at high rpm with this simple swap to a carburetor jetted for 4,000 feet (49/66). Jon also retarded the ignition timing a couple of degrees to reduce the risk of detonation and improve the torque curve. Another solution would have been to tune the distributor and curve it for Jamie's manifold, carburetor, and camshaft combination.