boosted Gas Mileage, wow
HCF Member
Joined: Oct 2005
Posts: 178
From: Omaha, NE
RE: boosted Gas Mileage, wow
ORIGINAL: sacicons
anything other than displacement that adds power does so by increasing the efficiency of the motor, so if you are using the more powerful motor approximately the same as you would have used the less powerful motor, then mileage should go up. notice he said he wasnt grannying it either, but he didnt say he was driving noticeable harder than norrmal either. hell, if he did granny it, hed probably break 50 mpg.
anything other than displacement that adds power does so by increasing the efficiency of the motor, so if you are using the more powerful motor approximately the same as you would have used the less powerful motor, then mileage should go up. notice he said he wasnt grannying it either, but he didnt say he was driving noticeable harder than norrmal either. hell, if he did granny it, hed probably break 50 mpg.
Boosted cars sometimes get good/better gas mileage because the compressors heat up the air which helps atomize the fuel better. Once you start hitting boost, you require more fuel which will not increase mileage.
Between Phoenix and Denver I got a best of 31-32 mpg on my stock SHO. Once I put a Vortech supercharger on, my milage went to 26 mpg @ 80-85 mph and 24 @ 100+ mph. Obviously, as you go faster you work with more drag. Much of the loss in gas mileage was due to my foot and the richer tuning during engine deceleration.
HCF Member
Joined: Jun 2004
Posts: 7,699
RE: boosted Gas Mileage, wow
but comparing a smaller boosted motor with a larger one that weighs the same doesnt work out in favor of the larger motor, because a boosted engine (usually) has higher VE, which will make more power, while wasting less. and im thinking your mileage went down partly because it was boosted previously, so you are probably messing with the VE of your stock motor, and its probably running pretty rich, esp with a supercharger, which runs kinda hot anyway, so it would need to run a little rich if you raised the boost, unless you had water/alcohol injection or something similar to lower intake temps. a turbo can raise the VE even more, since it is using wasted exhaust gas heat to compress the air, instead of the crankshaft.
HCF Member
Joined: Oct 2005
Posts: 178
From: Omaha, NE
RE: boosted Gas Mileage, wow
The smaller engine and larger engine in comparison would not weigh the same. The supercharger would not make up the missing weight you would find in a larger engine. Both motors, small and large, at 50 hp are burning approximately the same amount of air:fuel.
Also, my motor was orginally normally aspirated. I later added a supercharger with 11 PSI. Even if I was boosted stock, adding more boost would only burn more fuel under higher boost pressures as MORE air is making it into the motor. I DO have water injection, 2-stage to be exact, but it is not activated until you see boost. The first stage is at 4 PSI and the second is activated at 8 PSI. Regardless, cruising would not be affected.
Under cruise conditions, the engine does NOT need to run any richer. The extra heat created under little to no load is not enough to cause detonation at part throttle. If anything, the extra heat will help atomize the fuel better.
VE does not refer to the parasitic loss through being run off a crank versus exhuast driven. If you look at the definition of VE, you'll find it says nothing about parasitic loss. It is about how much air you can get into the cylinders.
Also, my motor was orginally normally aspirated. I later added a supercharger with 11 PSI. Even if I was boosted stock, adding more boost would only burn more fuel under higher boost pressures as MORE air is making it into the motor. I DO have water injection, 2-stage to be exact, but it is not activated until you see boost. The first stage is at 4 PSI and the second is activated at 8 PSI. Regardless, cruising would not be affected.
Under cruise conditions, the engine does NOT need to run any richer. The extra heat created under little to no load is not enough to cause detonation at part throttle. If anything, the extra heat will help atomize the fuel better.
VE does not refer to the parasitic loss through being run off a crank versus exhuast driven. If you look at the definition of VE, you'll find it says nothing about parasitic loss. It is about how much air you can get into the cylinders.
Volumetric Efficiency
The ratio of air inducted per cycle to the total displacement of the engine. Commonly referred to as the engine's ability to "breathe."
The ratio of air inducted per cycle to the total displacement of the engine. Commonly referred to as the engine's ability to "breathe."
HCF Member
Joined: Oct 2005
Posts: 178
From: Omaha, NE
RE: boosted Gas Mileage, wow
It will increase fuel usage..... When you are actually allowing more air into the motor by opening up the throttle body. Anytime you are in boost, you're taking in more air than you would NA, therefore using more fuel.
