In this day and age, when money is tight and the economy forces us to tighten our belts, we're all about free horsepower. While the big stroker fat-block is cool, along with that honking 6-71 blower, if the money isn't there, then you have to go about adding power the old-fashioned way-through dyno tuning.
With that in mind, we tackled the task of trying to add as much power as we could to this dream machine, a '69 Chevelle SS packing the legendary 396 big-block. Not the 375-hp version, this car's near-stock 325-hp engine was in need of some power. The owner was thrilled with his new toy, but less than ecstatic when it clicked off mid-15-second elapsed times at the drag strip. Now, 325-horse/automatic Chevelles were not 13-second rides from the factory, but we figured a high-14 was within the realm of possibility. We wanted to see what this bad boy made to the rear tires.
Equipped with a stock Quadrajet, and only enhanced with an Edelbrock 2.0 polished intake manifold and a set of Flowmaster mufflers, this Glacier Blue A-body was perfect for a chassis-dyno tuning session. We hauled our test mule down to Tune Time Performance in Toms River, New Jersey, where we strapped the Chevelle to the Mustang dyno in search of some free power
In addition to seeing what the car made near-stock trim and what we could squeeze out of it, we also decided to pit the Quadrajet (enter your favorite detracting name here) against a pair of Holley carbs we had lying around. We brought with us a Holley 750 HP double-pumper and a Holley 670 cfm Street Avenger vacuum secondary mixer.
We started out by baselining the Chevelle, but had to abort the first pull because the air/fuel reading showed that the engine was way too lean (16.1). After adjusting the mixture screws on the the Quadrajet, the 396 pumped out 199 (corrected) horsepower and 274 lb-ft of torque.
With found the base timing coming in at 42 degrees overall, so this was the first tweak. We added 8 degrees, bringing the timing total to 50. We let the car rip again, and found six horsepower, bringing the total to 205, but more importantly the torque figure checked in at 284 lb-ft, a solid 10 lb-ft improvement.
With the Quadrajet pushing out as much as it could, we swapped to the big boy of the bunch, the 750 HP. After modifying the fuel lines as needed, we let the big-block sing once again, and even though the engine was now, as overheard by onlookers, "pig rich", the Chevelle eked out 206 horsepower and 291 lb-ft of torque. With the air/fuel well into the 11.5:1 range, we swapped the jets both front and back in search of a leaner reading and hopefully more horsepower. While the air/fuel settled in at 12.5:1, the power remained the same. While we gained one horsepower and seven lb-ft of torque, the 750 HP would certainly have proven to be more favorable if the Rat was inhaling through something like an Edelbrock Performer RPM and exhaling through a set of headers instead of factory manifolds.