This is a true test of ramp speed. That is the only difference between the two cams in the graph.
The TA cam has the standard hydraulic cam ramp opening and closing rates, while the GSCA cam has "fast ramps".
Remember, these are identical spec cams, installed at the same intake centerline, in the same engine, by the same engine builder.
|
Actual Numbers |
GSCA Pop Mech |
TA Stocker Shootout |
|
Peak Horsepower / RPM |
464 @ 5500 |
475 @ 5700 |
|
Peak Torque / RPM |
500 @ 3000 |
492 @ 3200 |
|
Averages 3000- 5700 Rpm |
||
|
Horsepower |
395 |
404 |
|
Torque |
465 |
468 |
We see that the GSCA cam makes more power below approximately 3200 rpm. Between 3200 and 5500, the power outputs are similar, with a slight edge to the TA cam. The real difference is what happens at 5500 RPM. The GSCA cam experiences lifter failure, and power drops off dramatically. This has nothing to do with this engine's inherent ability to breath at high rpm, rather the valve train stability is the limiting factor. These two cams were tested in the same engine, and are identical in every way, the only difference is lobe profile.
A 235/245 duration camshaft is not a small cam, and one would expect a properly prepared engine to want to make power in the mid and upper rpm ranges.
One should also note the smooth power increase in the engine, with the TA cam. This is due to the fact that the engine's valve train is operating properly, even at the lower RPM ranges, and airflow is increasing proportionally with rpm.
This engine, with either cam, wanted to make power to 6000 RPM. The real difference here is that one cam would allow it to attain that RPM, one would not. The TA cam will allow the engine to be shifted at 300-500 Past the HP peak, which has reduced a vehicle's ET, in my 15 years of experience, relating dyno power figures to on-track performance.
In my opinion, there will never be any great difference in performance, in a 455, regardless of the airflow abilities of the engine. The only real factor is, in a modified engine with increased airflow potential, the rpm limitations of the fast ramp design.
Valve train durability is in question with some very aggressively lobed camshafts. While I was preparing this site, I was contacted by a fellow club member concerning this issue.
Dear
Mr. Weise,
I read with concern your comments on the GSCA website about their
Popular
Mechanics 116 camshaft, mainly because I had just installed one in the new
engine for my 1970 GSX. It concerned me enough to contact the president of the
GSCA himself (Mr. Lasseter), who assured me there was no problems with the 116
cam.
Unfortunately, on only the third pass through the gears( approx. 5000 rpm)
with the new engine, I had a rocker shaft break. The rockers and shafts are
brand new steel replacement units. I understand your concerns about this
camshaft center around the valve train harmonics, do you suppose my broken
rocker shaft could be a result of these same harmonics? I am a bit worried that
this will be a re-occurring problem.
I look forward to your response as I am on a rather tight budget and can't
really afford to keep breaking parts. Thank you in advance
Al Fiandaca
1970 GSX
1971 GS(GSX clone)
1986 GN