6-71 BB, gas mileage

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tooslow

tooslow

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This is a stupid question but i am going to ask it:
My normally aspirated 850 CFM Dodge 440 gets 4 MP at 70MPH(3100RPM)
I have purchased a new 6-71 blower and dual 750's for my 440 / The pulley's are 10% under driven so maybe 6-8psi of boost
No other modifications will be made to the engine or drive train
Next week I will start the installation
Larger fuel pump, lines, and boost referance mods will be made



With this combo will my mileage be Worse criusing at 70MPH or about the same??
 
Damn, that's worse MPG than a fully loaded Freightliner tractor trailer!
(way worse). Im guessin that you need to drive a little slower (haha).
The blower wont help anything. What's the A/F ratio. is it running rich? I dunno...
Hope the engine is set up ok fr the blower, lower compression etc.
Where the heck are you driving around in IL at 70 mph, hopefully not through Chi-town!
(jus bustin ya chops. lol)
 
I live on the outskirts of Chi-town. I love to drive my car on the highway and backroads out by Wilmington!!! People are running 80mph and i go with traffic. I am a driver vs a polisher
I was HOPING that unless i had my foot in it the mileage would be about the same.
To late now and i will find out. Blower piurchased
Maybe i will change to a polisher and not a driver-Its all Good
My engine is a 496-440 and the hottest built motor I have run to date
Sucks the most gas to date also:pale: (fun to DRIVE)

12 gallon fuel cell and may have to re-think that
 
Yes and not much room for mistakes--Driveing it to my friends 4th party. 220 miles round trip $$$$$ Takin a gas can!!!


I am going to start a motor, rear gear mileage thread--I hope people respond this should be interesting
 
So, how about that first mod being a trailer hitch and a small trailer with a huge fuel tank on it?
 
The trick you have to do is put a higher gear in the back end once you put the blower on. With all the extra torque the blower will give you, you can do that and get better mileage.

Jack
 
With your speed vs RPM I'm guessing you're running 3.55 gears which ain't bad for the highway but your mileage sucks bigtime there is something wrong. I'd be looking at that carb running way rich (pull your plugs and take a look at them) or your timing is completely out of wack. If you've got your vacuum advance disconnected from the dizzy hook it back up that'll help and what kind of compression are you running for this blower. Before I would go bolting on a blower I'd make sure that engine is tuned properly to the way you're running now cuss a blowers a whole new keddle of fish.
 
I've ran several blower cars over the years and 4-8 MPG is about average with a 6-71 on a big block, but curb appeal and throttle response made it worth it.

IMHO, if you were looking for an MPG upgrade, then a turbo, or centrifugal/screw type compressor would be more advantageous, but I do understand the appeal of a big roots setup.

On the 440, I'd also have to agree. The mileage isn't that great, and I'd keep an eye on the oil to make sure it's not gettting fuel "fouled" - before the supercharger goes on. Also be aware that most "boost referenced" carbs are jetted rich to avoid a potential lean out condition, which will destroy most engines.

Another area to be cautious with is blower belt tension. I've encountered several hobbyists over the years who over tighted the idler pulley. Problem is, all that aluminum will "grow", significantly once everything comes up to temp - and the belt WILL NOT stretch. It will wipe out your number 1 main bearings and potentially destroy the rotors and case... Initially, run the belt loose and take up the slack once it's up to temp. Yes, when it's cold, the belt will be very loose. That's normal.

The other area to be cautious about it the crankshaft key. The factory key will not do the job. You'll need to add another key slot and key (180 degrees apart) to keep the kenetic energy from the blower from stripping your "hub" (since a stock balancer won't work either).

With that said, my oil changes increased based on fuel fouling, since even after jetting the carbs down, 2 4 bbl carbs (they run in parallel) at cruise are still going to dump considerable fuel.

I hope this helps and do share some pics !

Southernman
 
Southernman,
Very well said and thank you. I don't think I've ever had anyone explain the belt tension in a way I understood before. (Most answers I got were of the just cuz variety).
 
I am still flippin out that "6-71" "BB" and "MPG" are the title of this thread. LOL
 
My Speedo was off and 70mph was actually 87mph. Lucky smokey didn't me!
Recalibrated speedo and criusing 60 gets me 7 MPG. Just an update
 
What nice about a supercharged engine is you can run mild gears, mild camshafts that should do better than a n/a engine with a radical cam. And make power and street manors that a n/a engine could never touch. With a proper blower cam, and set up right you will be amazed of the power.I dont remember what my 440 did, but we put a 6-71 on a stroked 340 on a demon that got 15 mpg highway with 3.55 gears , mild blower camshaft.
 
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