The Sound Of Power

COMP’s new Thumpr line of camshafts delivers power and that great musclecar sound

Tim Cole from Competition Cams

Great advancements come at the intersection of inspiration and need. Thermal underwear, for example, sells a lot better in Minnesota than Florida. Lots of people have great ideas but can’t find anybody who wants them. The trick is to match the inspiration with the people’s needs.

“We’ve interviewed hundreds of people at car shows and speed shops,” said Tim Cole from Comp Cams. “These were all people who were thinking about or in the process of buying a camshaft for their car. They were going to buy a new camshaft, and we found out they had two main criteria. Number one was better performance. That one was obvious. Number two: They told us they wanted the cam to make their car sound downright mean. Shortly thereafter we had an experience that really set things into motion. At one of the car shows this good ol’ boy from Alabama was talking to a member of our team and he said, ‘I want you to build me a cam, and I want that mother to thump.’ And that’s when the light went on. That’s what started it all — the birth of the Thumpr camshaft line.”

The Target

Thumpr™ cams are designed to deliver the rough, racy exhaust note associated with big, carbureted race engines but retain their street manners. The problem with all-out race cams is they’re designed expressly for one purpose. They may run like a scalded dog at high-rpm levels, but they can also be miserable to live with on the street. Acceleration from idle and behavior at lower rpm levels can be notoriously poor.

A Thumpr cam, however, is designed to provide the full-throated sound of a race cam with be perfect for gearheads who want their cars to sound as good as they run — everywhere. That means they can have a lumpy, intimidating idle and still drive the car to work every day. Or better yet, cruise night or car shows and church on Sunday.

Just ask Lee Watson, one of the first people on the planet not affiliated with Comp Cams to put a Thumpr in his car. “I have a ’32 Ford three-window Highboy Coupe. It had the 350 horsepower Chevy 350 crate motor in it, and I was looking for a different camshaft,” he says. “I’m also involved in drag racing, so I knew Comp Cams and Tim Cole, and he told me about these new Thumpr cams. So I installed one along with a set of roller rockers. I love it. The cam sounds great and it’s got both low-end and top-end power. Everybody that hears my car says, ‘Man, that’s badass!’ It’s just a really nice cam.”

The Thumpr CL Kit includes cam, lifters, assembly lube, decals, and instructions.

How they work

Normally, drivability is built into a camshaft by building in good low-end torque. This means optimizing the camshaft to work better at lower rpm levels by shortening up the duration (the amount of time the cam holds either the intake or exhaust valves open) and reducing the amount of overlap (the period when the cam has the exhaust valve closing and the intake valve opening at the same time). It also makes a motor quieter by keeping the exhaust valve closed longer. A Thumpr, however, breaks the rules and does it successfully by enhancing the exhaust note while maintaining drivability.

“The Thumpr cams aren’t designed around lobes we just pulled out of the catalog,” Cole explains. “They had to be specially designed to meet our performance goals. With the Thumpr™ cams we increased the amount of overlap, because the exhaust side of the event is what you hear. By increasing that overlap window, we achieved that great sound. The Thumpr cams are also ground on a narrow 107 degrees of lobe separation. For comparison, most of our popular Xtreme Energy cams are ground with a 110-plus degree lobe sepa-ration angle. The cams are also ground with five degrees of advance in them, putting the intake centerline at 102 degrees, which puts a lot of torque back into the motor that the increased duration would try to water down in the normal world. These lobe designs are popular in thin air and summertime applications. Customers in Denver love the Thumpr cams because the things we do to make them work are the same things we do to make a cam work at high altitude anyway.”

Watson says that the increase in torque is something you can definitely feel in the seat of your pants. “My street rod has a high 3:1 gear in the rearend. I can step on the loud pedal, and it will carry the left-front wheel through the intersection. So it has definitely got the performance to back up the sound. It’s not all show and no go. But it also idles down to 700 rpm,” he adds. “I’ve got air conditioning in the car and the whole business. It makes plenty of vacuum. I just took the cam out of the box and shoved it in the hole and I’ve been driving it ever since.”

The Thumpr GK Kit includes cam, lifters, gear drive, assembly lube, decal, and instructions.

The Power of Choice

Currently, COMP offers the Thumpr cams in three different flavors in increasingly radical grinds for carbureted engines. The baseline is the Thumpr for smaller or more basic engines. For Chevy small blocks Thumpr cams are the most popular option. Thumpr cams also usually work well with other OEM valvetrain components so that the costs of upgrading are minimized. While the duration is increased, the lobes are still gentle on valves and springs so that the increased performance doesn’t result in the valvetrain flying apart. Total valve lift is also held in check to keep shorter stock springs out of coil bind. Cole says that when the displacement ramps up toward 383 and 406 cubic inches, they become candidates for the next level, the Mutha Thumpr. In small-blocks, the most extreme level, the Big Mutha Thumpr™, is best reserved for street/strip cars that spend more time on the strip than the street. As Cole says, “The Big Mutha Thumpr is a really serious cam in a smallblock; it’s not for the faint of heart.”

But for someone looking to stuff a Thumpr™ cam in a big-block engine, the extra cubes make the standard Thumpr™ a bit tamer. Many big-block owners choose to go with the Mutha Thumpr™, which can handle a more radical lobe design without a problem. COMP now has Thumpr™ designs in all three levels available for most makes and sizes of V-8 engines. Lobe designs are available to work with both hydraulic flat tappet lifters as well as hydraulic rollers. So if the owner already has a hydraulic roller cam, he can save some bucks by reusing his roller lifters. That means the choice is up to him.

All three levels of Thumpr™ cams increase power over stock cams, so the real choice is how much “Thump” do you want from your engine? One of the best ways to get a feel for how each level of Thumpr™ cam sounds is to go to Comp Cams’ website and check out the information section on the Thumpr™ lineup. There you’ll find recordings of engines with each level of camshaft so you can hear with your own ears the incredible rumble they make. So now, as Cole says, a Thumpr™ cam will let you have both the sound and the fury.