Ramp
Speed comparison test.
A lot has been made of the “latest thing” in cam design. The
“fast ramp” cams seem to be all the rage these days, especially in
Buicks. The theory goes like this:
“For
a real full weight street GS, why design a gentle-lobed cam that will rev to
6000+ RPM when your
engine makes peak horsepower below 5500 RPM? It makes a lot more senses to
design a cam with more aggressive lobes and a wider lobe separation, (less
overlap = better idle) that offers more “breathing area” under the valve
lift curve to produce peak horsepower at the RPM the engine will make it’s
most horsepower! … Who cares if the cam will run to 6000 RPM if the engine
makes its maximum horsepower no higher than 5500 RPM regardless
of cam!”
--Richard
Lasseter, Nov-Dec 2000 GSXTRA pg. 6
Wanting
to test this theory, and since one of TA’s new cam designs was very similar to
a popular “fast ramp” profile, a test was run, to compare the two. The TA
cam has a standard ramp hydraulic cam profile, and has considerably less lift.
Duration numbers are nearly identical, and the lobe center separation of the
cams is only 1 degree apart. Certainly, with a fast ramp profile, with more
lift, and 3 degrees more exhaust duration, the Straightline Performance cam
should out-power the TA Street Intimidator.
Engine components
Stock
intake
Q-jet
carb
Shorty headers
|
Actual Numbers Measured |
Straightline cam |
TA Street Intimidator |
|
Peak Horsepower / RPM |
439 @ 5900 |
434 @ 5700 |
|
Peak Torque / RPM |
456 @ 3300 |
458 @ 3300 |
|
Averages 2900 - 5900 |
||
|
Horsepower |
358 |
363 |
|
Torque |
430 |
437 |
A huge factor is being overlooked with the fast-ramp philosophy. The
variable is valve train stability with hydraulic lifters.
A smooth acting, stable valve-train will allow the engine to produce the
most power, as proven by this test. Straightline’s
fast-ramp cam would rev to 6000 rpm, as it’s ramp speed parameters are within
the acceptable range for a hydraulic camshaft. But it made no more power than a
“gentle lobe” cam.
Also see a direct comparison of the GSCA “Popular Mechanics Shootout Cam” to an identical cam, (the only difference being ramp speed of the lobes) which is sold by TA Performance.