Greg Smith had a problem. His 55 had come up lame, and he wasnt sure what it was. It just lays down at the top of First gear, he said. The 55 used to be a stab-it-and-steer-it 12-second car with its 355ci small-block, Turbo 400 trans, and 4.33 gears. But lately the car had slowed down considerably and now was running disappointing 13.20s at 106 mph.
At first, friends all chipped in with suggestions. Greg improved the fuel delivery system thinking that the motor wasnt getting sufficient fuel. He added a big electric pump and lines, but the problem persisted. Then he borrowed an MSD-6A ignition box and distributor and while the throttle response improved dramatically, the cars performance was still lame.
Finally, someone suggested checking the valvesprings. This made sense since Greg has always shifted this engine up around 6,800 rpm. While Greg doesnt drive the car on the street much, it has seen its share of dragstrip duties over the years. Greg pulled both valvesprings from the No. One cylinder and trekked down to his local machine shop where they pronounced the springs mortally wounded. The seat pressure that should have been around 100 to 105 pounds was down around 80 pounds, while max lift pressure was proportionately low. Clearly, it was time for a new set of springs.
Spring Death
So what killed these springs? The smoking gun lies with rpm. Everybody likes to buzz the motor to the moon. Theres nothing that sounds sweeter than a small-block revving to 8,000 rpm as the driver rows his way through the gears. But this same rpm is absolutely death on valvesprings. In Gregs case, the springs were of questionable origin and had been on the engine for many moons. Subjected to hundreds of rpm blasts both on the street and on the track, the springs finally gave up and lost much of their original pressure.
When the spring can no longer control the valve, the engine goes into what is called valve float. Most enthusiasts think this means the valve launches off the nose of the cam at max lift and can smack the piston. While this can happen, the more common occurrence is the valve bounces off its seat upon returning to the closed position. In the case of the intake valve (which is heavier than the exhaust), this bounce contributes to lost cylinder pressure because the valve is off the seat when it should be closed. The less pressure the spring exerts on the valve, the more times it will bounce and the more cylinder pressure is lost. This is why the engine just quits revving. That was Gregs complaint with the car.
The Fix
The good news is that the fix is easy. All you have to do is choose the proper springs for the cam, and the cam manufacturers have already done that for you. In Gregs case, the cam was a big Crane mechanical flat-tappet cam with 0.554/0.572-inch lift (see Cam Specs for the details). The combination requires a stout dual valvespring. We also double-checked to make sure the new spring diameter was the same so no machine work would be necessary.
Once the springs arrived, Greg used a slick valvespring compressor tool from Moroso to remove the springs. The photos reveal how easy this was, but dont be fooled. The job still took the better part of the day to complete, but that was mostly because the 55 Chevy engine compartment was somewhat confining, and also because the headers had to come off in order to install the compressed air attachments.
Greg also took the time to carefully measure each springs installed height to ensure that the springs would have the proper pressure (see The Right Height). This added to the time it took to complete the job, but its the right way to do it. With the springs installed, Greg bolted the Crane gold roller rockers back on, set the lash to Cranes spec, and fired the motor. After readjusting the valve lash when the temperature came up, he was ready for a quick test run. There wasnt time to go to the dragstrip to test the car, but Greg reports that the car feels much stronger and will now rev right to 6,800 rpm without a problem.
Valvesprings may not be very glamorous, but they are an essential component if you are going to buzz your motor much past 5,000 rpm and expect it to make power up there. Match the springs to the cam and install them properly, and you can expect healthy horsepower dividends.