After a drag test of this Glacier Blue '69 Chevelle SS396, we decided a trip to the chassi
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.
Not only would we tune up our Qaudrajet-equipped 396/325 powerplant, but we would also try
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.
Before a dyno pull was made, contributor Dan Foley checked the timing of the Rat, and he p
After an aborted first dyno pull that forced us to adjust the Quadrajet, the Rat thumped o
Satisfied we weren't going to make much more power with the Quadrajet, we swapped over to
Last but not least was the 670 cfm vacuum secondary Street Avenger carb supplied by Holley. We slapped this puppy on, rigged the electric choke to stay open, and fired the fat-block Chevelle up. After playing with the mixture screws, we stood on the loud pedal, where the 670-equipped 396 recorded 195 hp and 281 lb-ft of torque. With the air/fuel reading for this car also being lean, we made a primary side jet change. The jet change made a difference in the air/fuel reading on our last dyno pull of the day, as it lowered it from the 14.0:1 range to 12.7:1. The Chevelle missed the 200 horsepower mark, though, recording 199 rear wheel horsepower and 287 lb-ft of torque
Overall, we spent a day at the dyno with a big-block Chevelle, and drove out with seven horsepower and 17 lb-ft of torque more than what we went there with. While we could have spent the money on either of the Holley carbs and made respectable power, but adjusting the mixture screws on the Quadrajet and adding timing to the engine, we picked up 10 lbs-ft of torque and six horsepower just by tuning what we had on the car when we got to the dyno. For the price of what it would cost to have your muscle car chassis-dynoed and tuned, we would say it's money well spent.
The 750 was square all around with 73 jets, but we needed to lean it out a bundle. We drop
Last but not least, we laid down the 670 cfm Street Avenger carb atop the 396. Even though
Not wanting to mess with the great tip-in the 670 gave us, we only adjusted the primary si
Holley Performance Products, Inc.
1801 Russellville Road
P.O. Box 10360
Tune Time Performance