Quote:
Originally Posted by Vman455
Modding the engine to produce more power at a smaller throttle opening without changing the gearing does the opposite.
|
Hi Vman, do you have some numbers to back up this statement? It's pretty much opposite what my tuner and Torque Pro tools have told me, plus the old pencil and paper method.
Let's run your example another way...
You're climbing a hill, it requires 'x' amount of energy to maintain speed.
Car A is a 4 banger with typical 4 banger torque band with a curve and peak around 4k RPM, Car B is an efficient V8 with flat torque curve and peak around say 2500RPM as is very common in today's engines.
For sake of argument both cars are geared the same, same size tires, etc.
Now both cars hit the hill at the same time, and to maintain speed Car A must really open the throttle to achieve enough power production to climb the hill, Car B cracks its throttle.
By your logic Car A is using less fuel because it's a small engine making more power per displacement, hence is more 'efficient' because of that ratio, correct?
However! To achieve this type of efficiency the engine is 'working' harder. When the throttle blade opens to allow in more air, you have to have more fuel added at the same time to make things work, air alone can't produce 'energy' from an engine. To see this in real life hook up your tuner or scanner device and set to watch your injector pulse width, short term fuel plan, etc.
Or if you're analog another fun tool is a vacuum gauge. Your 4 banger with the throttle open is drawing much less vacuum than the V8 with cracked throttle. You can argue that means the 4 banger is more efficient based on the above statement, OR you can also realize that on all vehicles with vacuum regulated fuel systems your fuel pressure regulator is now opened wide allowing 40psi to the injectors, which are also pumping at say 85% duty cycle in order to meet the power requirements of this hill, vs Car B which isn't working hard, still drawing good vacuum, fuel pressure is lower, injector duration is lower, etc.
Making sense so far? The problem with the efficiency models the way you describe is they look good on paper, but tend to sink in real life. When you look at the numbers in terms of how the engines are functioning, all the non-black and white perfect physics variables that are going into making Car A much more complicated than 'HP per L' efficiency...
To use another example that's really going to mess with your head, aerodynamics. Why does reducing drag improve fuel economy rather than improve it? According to your statement above (new Car A and Car B are now the same cars except Car B has some aero mods) Car A should get better fuel economy because the engine is working harder to maintain the same speed due to increased drag on the vehicle, requiring more power to stay at speed. Higher power requirements means the engine's throttle is open more, means that engine is more 'efficient' as it is producing more power than Car B's engine that is working less hard to maintain speed as the vehicle is more slippery and doesn't require the same energy to overcome drag.
Ruh roh...
Yep that's right, in real life the more slippery version, Car B, gets better fuel economy than Car A even though its engine is 'less efficient' than Car A's as it is producing less power to keep the car moving at the same speed.
Same thing with the Top Gear episode everyone poo-poo'd because it's obviously against popular edict here, let's change the scenario one more time but keeping with their test ideas:
You have 2 trucks pulling say 8,000lbs of trailer. Truck A has the smaller gas engine option, truck B has the bigger gas engine (no diesel here to complicate things). Which truck will get better fuel economy? All else is equal, rigs are essentially the same weight, same aerodynamics, same gearing, etc.
Truck A has to work really hard to get its load moving vs Truck B because it has less power under the curve, which according to your logic means Truck A is getting better fuel economy because it's throttle is wide open and is making more power per L vs the bigger engine Truck B which is just loafing along. Truck A has to work really hard to KEEP its load moving at highway speed vs Truck B, same reasons as above.
Which truck is going to have the better fuel economy? The more 'efficient' Truck A, efficient because it's making more power per L to move its load, or Truck B which I argue is the one that's really more 'efficient' because the engine isn't working nearly as hard, ergo the engine is in fact burning less fuel per L displacement because it has much more power under the curve and you don't need to open the throttle as wide to achieve the same power output as Truck A required to achieve the same end results.
Head hurt yet? I need some caffeine, and my chickens are getting hungry...