breathing new life into a 383 sbc

The car is a 1973 Camaro with a 383 SBC stroker and a 4-speed manual transmission.   Engine modifications include an Eagle 383 stroker rotating assembly that yields a pump gas friendly 9.5:1 compression ratio, aluminum ProMaxx cylinder heads, hydraulic roller camshaft and 1.6 ratio roller rocker arms, dual plane intake manifold, long tube headers, MSD ignition, and a Holley Sniper EFI system.  I was told that the engine made 500 horsepower on an engine dyno prior to installation.  The 12-bolt GM rear axle sports 3.73 gears.    

The car ran well, but was lacking the low end grunt that I felt it should have for a street driven vehicle.  Upon closer analysis, I discovered that the hydraulic roller camshaft sported 236/242 duration @ .050" and the lobes were ground on a 110 degree separation angle.  In my experience, this is too large for this application and definitely not the best choice for the Sniper EFI unit to work without the occasional issue.  Our performance objective was to increase drivability without sacrificing top end power.  

The plan was to swap out the over-sized hydraulic roller for something a little better suited for the street.  I was confident that we could "fatten the curves (horsepower and torque curves)" down low in the RPM range without sacrificing significant power higher in the RPM range.  Given the relatively modest static compression ratio of 9.5:1, it was important to remain conservative with camshaft timing so that we could trap as much cylinder pressure as possible at low to moderate engine speeds.  A grind from Comp Cams was selected that sported 218/224 degrees of duration at 0.050" valve lift on the intake and exhaust respectively.  Lobes were placed on an EFI friendlier 111 degree lobe separation angle.        

Before we started any work, the car was loaded onto the SRS Superflow chassis dyno so that we could establish a consistent baseline.  We wanted to be sure that the final outcome was as objective as possible and that we were not basing our results on our "seat of the pants" feel.  The combination produced power that was fairly consistent with similar builds.   

After the camshaft change, some significant work was required to bring the Holley Sniper EFI system back into tune.   We were required to add significant fuel to the entire table below 4,500 rpm.  This was the first sign that the cam change had made a significant difference to power output from idle to 4,500 rpm.  More air in requires more fuel.  In the end, the combination picked up significantly from  2,500 rpm (the starting point if the test) to 4,500 rpm.  Despite the much smaller camshaft, we only sacrificed 5 horsepower at 5,500 rpm (peak power).   The end result were much fatter horsepower and torque curves with minimal losses at peak rpm. 

The owner of the car was instantly over the moon with the added power throughout the curve.   "The car has never spun the tires like it does now" was one remark that stands out to me.  

Don't leave your engine combination to chance.  At Simpson Racing Solutions we have many dyno proven combination on file and we know what works.  If you are planning a new build or want to breathe new life into an existing build, we have the experience to help!  Contact us today 236.422.1180