2018-2020 Roush Supercharged 5.0L F150’s – Why Oz Tuning uses a larger pulley.
(Customer)
Hello, I was just wondering how lowering the boost gives you more horsepower.?
(Oz Tuning)
Lowering the boost AND tuning the truck gives more power than what the stock Roush tune with stock Roush pulley provides. Stock Roush pulley is too much boost for the intercooling system to keep up and air charge temps very quickly start to exceed the safe range. As air charge temps increase ignition timing must be retarded to protect against knock. On the stock Roush calibration, it’s very common to see single-digit ignition timing being commanded (I’ve seen values as low as 4-5 degrees of advance) because charge temps are well beyond the safe range (safe range is below 140*F). If you take a truck with the stock Roush pulley and tune on a dyno and make three back-to-back pulls on a dyno, you can see power drop as much as 200 whp from the first pull to the third pull, just because of the heat management issues these blowers have.
With our tune and pulley, we lower the boost to a range that doesn’t over-power the intercooling system. By doing that we typically see anywhere from 15-20 degrees of timing advance with good quality 93 octane. Just being able to consistently run more ignition advance makes a massive difference in performance and going from 5 degrees of timing advance to 15 degrees of timing advance could be a difference of 200+ whp. And additional benefit is that cooler air is more dense than hotter air. So, that means that oxygen molecules going into the engine are increased for each PSI of boost, as charge temperatures decrease. For example, 10 psi of boost with an air charge temperature of 75*F is roughly 15% more dense than that same 10 psi of boost at 150*F. Air that is 15% more dense has 15% more oxygen per mol and will make more power. That’s why when ambient temperatures start to drop everyone refers to is as “boost weather”. The cooler air is already denser, then when you compress that air with a turbo or supercharger and are able to cool it down even further, the air becomes even more dense. So, the engine will make more power because of the increased air density from the lower air temps and the improved ignition timing will also improve performance, and you also will not have severely reduced performance if you were to make a longer pull or if you did the same three back-to-back pulls on the dyno, all because lowering the boost brings the supercharger output into a range that the intercooling system can safely support.
Ken Osborne - Owner/Lead Calibrator
