trinydex
04-12-2007, 12:42 PM
torque can be loosely associated as a product of exhaust gas velocity. horsepower can be loosely associated as a product of mass flow. an example to clarify is that big horsepower cars flow a lot of air and what we view as torquey cars generally make thier torque low when the volume flow has high velocity. now i say loosely associated because gearing has to do with both factors and also because of what i'll explain next.
high horsepower engines with enough compensative gearing make high amounts of torque, however we do not view these cars as torquey but peaky. take for example an f1 2.4 liter v8. it'd be hard to convince me that this motor doesn't make a ton of torque at 16k rpms... but that's the problem isn't it... 16k rpms makes your car sound like... well an f1 car. so snap back to the real world for a second.
a typically torquey motor is the lsX motor where X can be 1, 2, 6, 7 etc... basically the vette/fbody motor. this motor generally displaces more than 6 liters so it flows a ton of air. but generally it flows at lower cylinder pressures than a turbo car like the evo. now with that basic qualification out of the way it doesn't matter.... now i say this because if you flow 1 pound through a 2 inch^2 hole... the hole loosely dictates the speed of the gas. that said the lsx's optimum flow is TYPICALLY at the midrange which gives you that low end torque feel.
now why did i say optimum flow? well because the cross section of the pipes going in and pipes going out of the cylinder dictate the flow speed and hence the torque (loosely again). so when you achieve optimum flow you achieve some level of peak torque (this can be modified). so if you made all the ports REAL big in the lsx would it then become peaky? absolutely. this is what's known as shifting the powerband or torqueband around.
see in the end this is a limitation of engineering, you're asking to maximize two fundamentally opposing quantities. here's the punch line. small flow area increases velocity but limits maximum flow potential, large flow area decreases flow velocity but increases maximum flow potential. NOW this is relative... what i MEANT to say was small flow area increases LOW END gas velocity but limits HIGH END maximum flow (tha last two adjectives were redundant) and large flow area decreass LOW END flow velocity but increases HIGH END FLOW VELOCITY which produces a HIGH END TORQUE!!! a bigger hole is idealized to a bigger flow.
if you had a 2" hole and it produced 100 foot/second flow speed at 4000rpm then a 3" might do the same at 6000rpm.
this is why in drag racing it's always better to shift the rpm higher, because you're never going to lose torque unless you can't gear yourself into the powerband.
if you cut yourself short by getting low end torque, you're LOSING HIGH END TORQUE!!!
now to answer your question of what gets you to keep the torque from dropping off. well the answer to any limitation of engineering problem is likely variable geometry of some sort. you can have a variable geometry turbocharger, this allows you to flow fast at the low end and fast at the high end... this creates a nice torque band that is relatively flat the whole way through, never dropping off while your hp increases the whole time. the other way is variable valve timing, you can change the flow characteristics/speed of the engine by changing the valve timing (mivec).
ball bearings and various sizings of turbos would only change what they call "static" quantities. in order to get the best of both worlds you need dynamic quantities.
high horsepower engines with enough compensative gearing make high amounts of torque, however we do not view these cars as torquey but peaky. take for example an f1 2.4 liter v8. it'd be hard to convince me that this motor doesn't make a ton of torque at 16k rpms... but that's the problem isn't it... 16k rpms makes your car sound like... well an f1 car. so snap back to the real world for a second.
a typically torquey motor is the lsX motor where X can be 1, 2, 6, 7 etc... basically the vette/fbody motor. this motor generally displaces more than 6 liters so it flows a ton of air. but generally it flows at lower cylinder pressures than a turbo car like the evo. now with that basic qualification out of the way it doesn't matter.... now i say this because if you flow 1 pound through a 2 inch^2 hole... the hole loosely dictates the speed of the gas. that said the lsx's optimum flow is TYPICALLY at the midrange which gives you that low end torque feel.
now why did i say optimum flow? well because the cross section of the pipes going in and pipes going out of the cylinder dictate the flow speed and hence the torque (loosely again). so when you achieve optimum flow you achieve some level of peak torque (this can be modified). so if you made all the ports REAL big in the lsx would it then become peaky? absolutely. this is what's known as shifting the powerband or torqueband around.
see in the end this is a limitation of engineering, you're asking to maximize two fundamentally opposing quantities. here's the punch line. small flow area increases velocity but limits maximum flow potential, large flow area decreases flow velocity but increases maximum flow potential. NOW this is relative... what i MEANT to say was small flow area increases LOW END gas velocity but limits HIGH END maximum flow (tha last two adjectives were redundant) and large flow area decreass LOW END flow velocity but increases HIGH END FLOW VELOCITY which produces a HIGH END TORQUE!!! a bigger hole is idealized to a bigger flow.
if you had a 2" hole and it produced 100 foot/second flow speed at 4000rpm then a 3" might do the same at 6000rpm.
this is why in drag racing it's always better to shift the rpm higher, because you're never going to lose torque unless you can't gear yourself into the powerband.
if you cut yourself short by getting low end torque, you're LOSING HIGH END TORQUE!!!
now to answer your question of what gets you to keep the torque from dropping off. well the answer to any limitation of engineering problem is likely variable geometry of some sort. you can have a variable geometry turbocharger, this allows you to flow fast at the low end and fast at the high end... this creates a nice torque band that is relatively flat the whole way through, never dropping off while your hp increases the whole time. the other way is variable valve timing, you can change the flow characteristics/speed of the engine by changing the valve timing (mivec).
ball bearings and various sizings of turbos would only change what they call "static" quantities. in order to get the best of both worlds you need dynamic quantities.