5.7L Hemi Performance: Cam Your Ram Part III, PSIched

In the previous two installments, we cammed our Ram and then followed up with a stroker kit in an effort to increase torque production. Both routes were ultimately successful in elevating the torque curve over the factory components. It wasn’t until the installation of the wilder custom hydraulic roller cam in Part Two that we started sacrificing low and midrange torque in a quest for top-end power. Cam timing usually has the effect, as ideal cam timing to maximum peak power is not the same as ideal cam timing to maximize torque production. The question is one of engine speed—or more specifically where do you want your torque curve generated? Wilder cam timing effectively shifts the torque curve higher in the rev range. The upside is increased top-end power, but the penalty of the shift is a loss in not only low-speed torque production, but likely overall drivability as well. The ideal world would be to have the power offered by both, or better yet, more power everywhere. Time to get PSIched!

As effective as the cam upgrade and even stroker short-block were, they actually pale in comparison to artificial aspiration, better known as boost. When it comes to boost, there are many available options, including multiple forms of supercharging and turbocharging. Every form has its strengths and weaknesses, but compared on a boost-to-boost basis, nothing beats the turbo. Blower guys will always chime in about the immediate boost response, which can be beneficial on low-speed truck applications where torque production is favored over peak power. Sized properly, a turbo can offer nearly as much low-speed power (torque) as a comparable supercharger, and do so at lower boost levels. The major benefit the turbo enjoys over the blower is the lack of parasitic losses associated with driving the blower. Power is required to drive any supercharger, the greater the blower speed and airflow supplied by the blower, the more power required to drive it. The power required to drive the blower is power not available to propel the vehicle, thus a supercharger must produce enough extra power to first offset that which was required to produce said power.

By comparison, a turbo is essentially given a free ride. On a normally aspirated or supercharged application, the exhaust (and heat) energy is simply allowed to escape to the atmosphere. On a turbo application, a portion of the otherwise wasted exhaust energy is used to spin the turbine wheel, which in turn spins the compressor wheel. The compressor wheel is what supplies additional airflow to the engine. Unlike the supercharger, very little power is consumed in this energy conversion, so the turbo does not suffer the same parasitic losses. The end result is that (properly sized), the turbo will always provide more power per pound of boost than a comparable supercharger. Of course, the turbo will not offer the immediate boost response of the positive displacement (roots or twin screw), but (for some) the extra power is worth the trade off.