Yes, if you stay out of the boost, supercharers can help w/ fuel economy even if you take into account the extra drag from the drive belt. Superchargers like turbos help to atomize the fuel more efficiently than a normally aspirated car. But, this is really only under light cruising conditions. Most everybody I know with a blower gets on it so often that the economy side just goes right out the window.
I think the only way you could make a valid comparison here would be to have two similar engines making the exact same horsepower, one supercharged and one not (so say a supercharged 302 with 8psi boost and a NA 460), in identical vehicles, same transmission (that would be tough) and compare the economy. Just taking any given engine, and adding a supercharger, or even a turbo, I doubt you would ever see a gain in economy. The only case I can think of would be maybe if you kept your foot out of it, then for instance if you were pulling a steep hill or heavy load that you would normally have to drop it a gear and rev it up (increased frictional loss), where with the supercharger you could keep it in high gear due to the extra torque, then MAYBE you would gain some economy due to less RPM/frictional loss.
I think the best way to figure if a blower would get you better economy would be to get two identical new Mustang GTs. One stock and one with a centrifugal blower. Fill them both up with the exact amount of fuel and take them out on the highway for a long drive together until you are almost out of gasl. Both cars would have to be driven exactly the same and the blower car would never be pushed into boost. At the end of the test, the blower car should have more fuel in the tank for the given distance driven.
This post makes me chuckle. My daily driver is a '94 chubby pickup, with a 5.7 tbi engine. The darn thing gets 10 to 12 mpg. On the highway, your foot is damn near to the floor to maintain 75mph. Ugh. The engine isn't tired, has new dynomax exhaust, well maintained etc... It's getting a supercharger this spring, not for power but just so I don't have to floor it the whole time I'm on the highway. Was gonna go with a whipple, but the model for my truck isn't made, so I'll end up with the holley mini blower. My theory, and this is just me, is that sometimes a gutless engine can hurt economy more than a capable power plant if driven correctly.
Matt, that holley mini blower should really wake up that motor and help with your mileage because you won't have to "matt" the gas pedal (sorry, couldn't resist that one). You are going with a carb I am assuming because the TBI will probably not be able to keep up with the fuel demands of that blower. But, if you are running low enough boost of say around 4-5 pounds, you may be able to get away with using the it. Those blowers will make power even when you are not in boost because the lobes are always spinning and compressing air even if it's slightly above atmosphere. You will definitely feel the truck move with much more authority.
I can tell you that my 89 T-Bird SC got 29-30 on the road and 23-25 around town, until it blew a head gasket at 249,000. I am fixing it now-going for 350,000-400,000 miles. Anyhow that is in a 3900 lb car and that little motor will move that car!! I could imagine how it would run in a 2800 lb. mustang. The secret is that is has an air-bypass valve so that if you are not in boost the blower is free-wheeling, more or less. Probably to get good mileage you would need fuel-injection after the blower and the air-bypass.
I was just looking for opinions and I got what I wanted... NOthing solid, because nothing solid was necessary... It's a mystery as to the fact of the matter and that is the way it shall stay, I like your opinions better than actual tests and facts in this circumstance.
I've driven normally aspirated cars and blower cars and while you can build a normally aspirated car to make a ton of power, there is nothing like forced induction. Period! I race with guys who run Procharged V-8 Mustangs that run in the high 7s and the amount of power they lay down is almost sickening. The way a blower car leaves the line makes a non-blower car look anemic. The turbo guys may make it up on the top end because of the inherent nature of the turbo being able to spool up in the higher rpm ranges, but the blower cars have it in spades everywhere else. One guy I know runs an early 70's Camaro with an F3 Procharger on an all aluminum big block Chevy w/ fuel injection pushing 2,000 horsepower on methanol. That car sounds like something from another world and when I saw it run for the first time last Summer, he could barely keep the front end on the ground the whole way down the 1/4 mile. All I can say is one you've been blown, you'll never go back.
That's all fine and dandy... I just preffer naturally aspirated engines.... I dont build a car that needs a blower to push it around...
I build a car to go and that's about it, not necessarily fast, but not slow either.
A fun car.
I was only thinking about the advantages to a supercharger or blower or turbo and that's why I asked the question....
Falconaround, I can see where you are coming from and I agree with you. But I think everybody should have at least one blower car just so they can see what it's like to be pinned in the seat so hard that it brings on a huge s**t eating grin. My next car will be normally aspirated because blower cars will get you in trouble really fast.
At lower RPM's I would have to say no. Why? Because while the blower doesn't have to build boost, it also has an inherent drag in the rotating parts.
It might help under load for the aforementioned reasons - no shifting down, more torque down low, keeping fuel consumption down, but with increased power also comes increased fuel consumption. You're not just increasing efficiency with a blower - in fact, you may not increase it at all. Just because it adds 100HP doesn't mean you're not using a proportional amount of fuel to gain that extra power.
I don't think it will help much, but the proof is in the pudding, as they say.