Here are a couple of graphs that nicely illustrate PRJs excellent point about peak hp numbers and compressive loading on rods/pistons.
As long as the timing curve is similar between two setups, the torque curve will give a good indicaton of what sees the highest compressive load. The lower rpm that peak torque hits, the higher the net compressive load, as the opposing tension load from piston inertia is much lower at low rpm (increases with the square of engine speed).
Graph 1: Power and torque (ftlbs) measured at the wheels.
Pay special attention to the torque curves. The blue graph shows my RS2 with stock bottom end and the yellow is the torque curve of a built 20vt with Comp 60/65 Billett turbo and 7A cams. It makes more peak power, but below 6200rpm, it makes less.
Graph 2: This shows my car vs the same engine, but with mechanical cams and a 64mm Comp turbo. The data is from a 1/4 run, so it is not all the way from low rpm. It makes 501whp on the Virtual dyno, and made 515whp and 550nm at the wheels on a Mustang dyno with the same setup (tuner runs 25% correction and quotes 685ps and 730nm at the crank). Note that it makes more peak hp, but less torque than with the 60/65 setup and hydraulic cams. Graph 3 shows these two setups in comparison.
The interesting thing that we see from this example is that my car is seeing much higher peak cylinder pressures and thus compressive load on pistons/rods (we both run E85) than a car that makes at least 630hp at the crank. These curves should also make it rather clear why I and others stress the need for high average hp on a street driven car and not just hunt peak hp numbers.
Graph 1: My RS2 vs 20vt with Comp 60/65 Billett and 7A cams:
Graph 2: My RS2 vs 20vt with Comp 64mm and 254deg mechanical cams:
Graph 3: 20vt with Comp 60/65 Billett and 7A cams vs. Comp 64mm and 254deg mechanical cams:
As long as the timing curve is similar between two setups, the torque curve will give a good indicaton of what sees the highest compressive load. The lower rpm that peak torque hits, the higher the net compressive load, as the opposing tension load from piston inertia is much lower at low rpm (increases with the square of engine speed).
Graph 1: Power and torque (ftlbs) measured at the wheels.
Pay special attention to the torque curves. The blue graph shows my RS2 with stock bottom end and the yellow is the torque curve of a built 20vt with Comp 60/65 Billett turbo and 7A cams. It makes more peak power, but below 6200rpm, it makes less.
Graph 2: This shows my car vs the same engine, but with mechanical cams and a 64mm Comp turbo. The data is from a 1/4 run, so it is not all the way from low rpm. It makes 501whp on the Virtual dyno, and made 515whp and 550nm at the wheels on a Mustang dyno with the same setup (tuner runs 25% correction and quotes 685ps and 730nm at the crank). Note that it makes more peak hp, but less torque than with the 60/65 setup and hydraulic cams. Graph 3 shows these two setups in comparison.
The interesting thing that we see from this example is that my car is seeing much higher peak cylinder pressures and thus compressive load on pistons/rods (we both run E85) than a car that makes at least 630hp at the crank. These curves should also make it rather clear why I and others stress the need for high average hp on a street driven car and not just hunt peak hp numbers.
Graph 1: My RS2 vs 20vt with Comp 60/65 Billett and 7A cams:
Graph 2: My RS2 vs 20vt with Comp 64mm and 254deg mechanical cams:
Graph 3: 20vt with Comp 60/65 Billett and 7A cams vs. Comp 64mm and 254deg mechanical cams:
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