The Thumpr Camshaft line of hydraulic roller camshafts from COMP Cams, introduced in 2006, has been a huge success, well beyond the company’s original sales estimations. For the uninformed, the Thumpr Camshafts are designed to produce good power and torque, as well as tremendous high performance sound through careful specifications.
Thumpr flat tappet GM camshafts available:
Small Block Chevrolet: ’55-98 model years 262-400ci.
Small Block Chevrolet: ’87-98 model years – OE Hydraulic Roller equipped
Big Block Chevrolet: ’65-96 model years – 396- 454ci.
Available for small- and big-block Chevy, small-block Ford and small-block Chrysler engines, Thumpr Cams are available in three sizes for each application (the Thumpr, the Mutha’ Thumpr, and the Big Mutha’ Thumpr). For folks looking for a hot performing camshaft that delivers great performance and wild camshaft idle, the Thumpr Cams could be the right call.
COMP Cams flat tappet Thumpr Cams offer the same great sound and power as their hydraulic roller camshaft cousins in an easy-to-fit flat tappet style. So the question arises with regards to camshafts, “Can you have your cake and eat it too?” In the case of our dyno test, we wanted to know if there was a camshaft that would not only deliver on the dyno, but would also enhance the sound of power derived from our engine for “cruise appeal.”
But while the roller camshaft application may be the best choice for many, roller systems are more costly than the early, more common flat tappet configuration used by many engines through 1987. COMP Cams created a solution for this with their new line of flat tappet Thumpr camshafts for small & Big Block Chevrolet as well as small block Ford and Chrysler engines.
Again three different profiles are offered each increasing the performance emitted. These camshafts are simple drop in units that do not require any other engine modifications other than a check of valve spring condition as would be the case with any camshaft swap. Standard hydraulic flat tappet lifters are used along with standard rocker arms and other valve train gear.
Steve Brule preps the small-block for its torture test!
How Does It Do That?
RHS (Assembled For Flat Tappet) SBC Heads (PN12023-01)
180cc runner volume
64cc volume chambers
Thumpr Cam (PN 12-600-4)
2000-5800 RPM Range
Lift: 0.479 Intake/0.465 Exhaust
Mutha Thumpr Cam (PN 12.601-4)
2200-6100 RPM Range
Lift: 0.489 Intake/0.476 Exhaust
Big Mutha Thumpr Cam (#PN 12-602-4)
2500-6500 RPM Range
Lift: 0.500 Intake/0.486 Exhaust
The basic science behind the Thumpr Cams is not a new one. The Thumpr line delivers true high performance engine sound by “tightening” the lobe separation angle of the camshaft. This creates more overlap between exhaust and intake events and more “cool” performance sound. It’s pretty simple science and while logic would have you believe that power is lost due to this overlap, our results have shown the performance is actually up over similar camshafts due to COMP Cams innovative lobe designs. And the public reaction has been overwhelmingly positive.
To test the real power found with these camshafts we enlisted the folks at Westech Performance to take the new flat tappet camshafts and test them head to head with the stock 350cid, 290 horsepower GM crate engine and an Xtreme Energy COMP Cams cam with similar performance specifications to these Thumpr Camshafts (actually it fits between the middle and largest camshaft in the line).
The results of our testing prove the mettle of the Thumpr cams, great power and torque, neither component compromised in the quest for great performance sound. If there is one area to note, it is the engine vacuum readings from the Thumpr-equipped engines.
Under the guidance of Steve Brule at the Westech Performance dyno facility, we subjected our dyno-mule to a severe list of duties, including a cylinder head swap from RHS, a Holley 750 cfm carburetor and multiple camshafts.
Let The Testing Begin
The following tests were run with the COMP Cams new Flat tappet Thumpr camshaft on the Westech dyno over three days in late December. The base engine was a time-tested 350cid 290 horsepower small block GM crate engine featuring a Weiand Air Strike intake manifold, 650cfm Holley carb, Hedman 1 ¾-inch primary tube headers, Magnum mufflers with 18-inch collector extensions and an HEI distributor system.
To that mix we added one set of RHS as-cast, assembled aluminum cylinder heads (180cc runner volume, 64cc chambers, angle plug design). The dyno test was run through a range of 2,600 to 6,000 rpm. For each configuration several tuning tests were completed – with the three best pulls averaged together to create a fair representation of the engine’s power and torque.
RHS Cylinder Head Swap
Test one included a cylinder head swap using the assembled RHS heads (Part Number 12023-01) delivered to Westech Performance. These are the as cast complete heads ready to bolt on with valve springs compatible with the Flat Tappet Thumpr tests to be performed. The stock ball-style rocker arms were used for this test.
Peak Power: 318 hp with 355 lb.-ft torque
Average power – 265.9
Torque – 327.7 lb. ft.
Vacuum noted: 15-inches
The RHS cylinder heads weren't mandatory, however, with the increase in lift and duration, they will allow the small-block to breathe and take advantage of each camshaft.
COMP Magnum Rockers
The following test involved the use of the first of the Thumpr flat tappet camshafts. Starting with the smallest of the three camshafts, Steve installed the 279T unit.
Results (279T) –
Peak Power: 341 hp with 376 lb.-ft torque
Average power – 285.1
Torque – 351.5
Vacuum noted: 9-inches
The Magnum rockers were used for this and all test to come.
Atomizing Fuel And Air
In testing, Steve noted that the engine was carburetion challenged. To fix that problem, he installed a 750cfm carb and tuned it appropriately. The 750cfm carburetor was left on for all subsequent tests. The new results with the 279T Thumpr cam were significant as evident by the jump in power and torque.
Peak Power: 357 hp with 387 lb.-ft torque
Average power – 292.4
Vacuum noted: 9 inches
Westech's "Magic-Man" Steve Brule installed the new Holley 750cfm carburetor on top of our small-block mule. Holley's are generally known for being ready-to-go right from the box. In this case, we were pleased and made almost no changes to the carburetor aside from adjusting the idle.
The mid-range Thumpr camshaft was tested next – part number 287T. All other parts were the same as the previous test including the 750cfm carb and Magnum 1.5:1 ratio rocker arms. Eugene Wald, Westch’s experienced tech, made each swap and assured that each camshaft would receive a healthy dose of cam lube before it was installed into the engine.
Results (287T) –
Peak Power: 376 hp with 393 lb.-ft. torque
Average Power – 299.5
Torque – 365.6
Vacuum noted: 7.5 inches
Second to last was the Thumpr 295T camshaft. Again all parts as the previous two Thumpr tests were retained. We were pleased with the camshaft as it made the most peak power and average power across the board. When compared to the baseline test, this particular camshaft made an additional 72hp and a healthy 40 extra pounds of twist.
Results (295T) –
Peak Power: 390 hp with 395 lb.-ft. torque
Average power – 302.9
Torque – 368.3
Vacuum noted: 5.5 inches
The final test of the session was conducted with the COMP Cams Xtreme Energy XE284 camshaft featuring similar dimensions as those to be found with the Thumpr 295T camshaft. The same parts and set up used in the previous tests were used again.
Eugene Wald makes sure each camshaft is lubed properly before going into the engine.
Results (XE284) –
Peak Power: 381 hp with 387 lb.-ft. torque
Average power – 297.8
Torque – 363.5 lb. ft.
Vacuum noted: 8.2 inches
What It All Means
While the Xtreme Energy camshaft showed a reduction in vacuum generated, the Thumpr camshafts were slightly more reduced and under the 16 inches of vacuum recommended for engine driving power accessories such as power brakes where vacuum is critical to safe operation.
The fix is to invest in the COMP Cams Electric Vacuum Pump that will ensure at least 18-22 inches of vacuum. This electrical pump is simple to install and only operates when vacuum drops below 18-inches.
If “cool is the rule” on the street, COMP Cams new flat tappet Thumpr cams are most certain to rule and continue the legacy started by its hydraulic roller camshaft cousins.
Our final graph illustrates each cams strong points and clearly shows the 295T as the clear winner with peak power coming in at 390HP and almost 400 lb.-ft.